DO THE TON

Blood Sweat Tears and Grease => Projects => Cafe Racers => Topic started by: JadusMotorcycleParts on Aug 20, 2017, 13:58:39

Title: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 20, 2017, 13:58:39
The title says it all.  This is going to be more of a speed and performance focused build than the last.  Less time and energy spent on finishes, more time spent on finessing and fettling.  I am hoping to implement and share a lot of ideas that both myself and other awesome members of this forum came up with through the process of the previous build.  The stock SR will get about 120kph, all Jadus bikes - both the test mules and the black standard get around 135kph.  All make around 20hp at the crank.  So looking to get 30hp with some trick mods to be able to get to 160kph or... the ton!

Something I noticed when I completed the black SR was that it was the nicest bike I have ever build, and I didn't/don't like it.  Not because I don't love it, but because I hate having nice things.  I hate the feeling of being 'precious' with something - not wanting to scratch the paint, not wanting it to get dirty etc.  That is why I will never own a nice car.  I want to use, thrash and trash my toys.  I don't want to spend time cleaning and polishing!  What a waste of time!  So this bike will be more along those lines and I can't wait to get stuck in.

I thought I would be ready to move onto the next model of bike to design parts for by now, but I feel I have one more good SR250 in me before that.  Who knows, maybe even more parts for the SR250 along the way!

The reason I want to document the build here is twofold.  One, I can share what I am doing with a greater audience, and two, it opens things up for a great discussion for ideas and allows me to get feedback from more experienced members of the forum who have 'been around the block' a few times  ;)

You can also follow the hashtag on insta:  #100mphSR250

Let it begin!  ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 20, 2017, 14:07:23
I have been holding off on starting this thread - waiting to make absolutely sure everything was tied up with the black bike.  But I started the thinking process long ago and have already got stuck in with a couple basics - engine out of the frame plus some angle iron supports in the frame.  This will allow me to run two projects in parallel - an engine project and a chassis improvement project.  The SR uses the engine as a stressed member, so messing with the frame (sitting on it, getting ride heights, foot peg positions etc) without extra supports is not a good idea - it would bend under load.

I have read a lot since I began building bikes as well.  All the books below I have read cover to cover and have many book marks.  Some of the mods I decided to do might sound strange to some, but I have pondered long and hard and have read and re-read about these mods to make sure.  I have also purchased a great chassis design pdf - more on that later.

Some of the number goals might be a stretch but I am absolutely confident I can get 160kph.  Will it be a first for an SR250?  Maybe not - if you know of anyone doing it, please point me in their direction  :D  100kg, possibly, 110kg, definitely.  30hp?  At the crank, yes, at the wheel, maybe 26!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: TranceMachineVienna on Aug 20, 2017, 14:20:30
I'm in man!!!cant wait to see thst thing finished!

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Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JMPUK on Aug 20, 2017, 15:02:39
This will be epic!!

Can't wait to see it
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Aug 22, 2017, 12:34:56
Like your other builds, I'm in! I also have had that Smith book for a very long time. Originally got it when interested in modding car engines.

One thing to suggest to your list of engine mods is thinking about pumping losses. There was an article by Dave Searle in Motorcycle Consumer News about this a couple months ago. Thumpers are notorious here because they don't have other cylinders working together to offset the crankcase pumping action. Many builders just vent their crankcases to look "cool" but it really doesn't do anything to decrease pumping loss (just keeps oily junk out of the carb like an oil catch can would); I got a Krank Vent off evilbay to experiment with creating a partial vacuum in the crankcase instead of trying to get all that air in/out of that skinny hose outlet (still planning). Krank Vents are a 1-way check valve and seem to be very popular with the H-D crowd as they reduce crankcase pressure and keep gaskets from blowing. My thoughts are that the engine will pump through the Krank Vent a couple times until the partial vacuum is created, then no more pumping.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: firebane on Aug 22, 2017, 16:53:46
This will be interesting. I had a SR250 that topped out about 110kph but vibrated like hell lol
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Hurco550 on Aug 22, 2017, 17:01:11
I enjoyed watching you last one, so of course im going to watch this one too =)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Aug 22, 2017, 17:39:53
I shed around 38kg from my RD350. It has a battery, a stock charging system, a heavily filled stock tank, all turn signals and lights. 30kg should be in reach without too extreme an effort for the SR. The wheels, forks brakes, fenders, seat, and a bunch of the other junk are pretty easily eliminated or replaced with modern bits. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 23, 2017, 17:24:05
Thanks for the support!

Like your other builds, I'm in! I also have had that Smith book for a very long time. Originally got it when interested in modding car engines.

One thing to suggest to your list of engine mods is thinking about pumping losses. There was an article by Dave Searle in Motorcycle Consumer News about this a couple months ago. Thumpers are notorious here because they don't have other cylinders working together to offset the crankcase pumping action. Many builders just vent their crankcases to look "cool" but it really doesn't do anything to decrease pumping loss (just keeps oily junk out of the carb like an oil catch can would); I got a Krank Vent off evilbay to experiment with creating a partial vacuum in the crankcase instead of trying to get all that air in/out of that skinny hose outlet (still planning). Krank Vents are a 1-way check valve and seem to be very popular with the H-D crowd as they reduce crankcase pressure and keep gaskets from blowing. My thoughts are that the engine will pump through the Krank Vent a couple times until the partial vacuum is created, then no more pumping.

Yepp, that is for sure on my list.  Someone (maybe even you?) posted some good stuff on the other build thread from the LS650 Savage forum about a system.  I'll see If I can dig that up.  It is also covered in these books :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 23, 2017, 17:25:07
I shed around 38kg from my RD350. It has a battery, a stock charging system, a heavily filled stock tank, all turn signals and lights. 30kg should be in reach without too extreme an effort for the SR. The wheels, forks brakes, fenders, seat, and a bunch of the other junk are pretty easily eliminated or replaced with modern bits.

True!  Thanks for the encouragement.  I'll start with the big obvious things then see what level I need to go into to shed the last few kgs.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Aug 23, 2017, 17:31:21
Hit me up if you have questions. I have a few simple but effective tricks beyond the common ones to get my RD down to the that weight. I didn't even have to spend that much extra dough, and in many cases the results were a vast improvement, the weight savings were just a bonus.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 24, 2017, 18:16:49
Hit me up if you have questions. I have a few simple but effective tricks beyond the common ones to get my RD down to the that weight. I didn't even have to spend that much extra dough, and in many cases the results were a vast improvement, the weight savings were just a bonus.

Sweet, I'll do that!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 24, 2017, 18:19:29
Managed to 'build' a 'rustic' table for filming some more install and tech vids.  Then found some time to blast the engine as well.  This time a pretty rough job compared to the last engine - running with the more time on performance things than looks!  I actually tried soda this time too, but it just wasn't abrasive enough to remove the clear coat on the engine cases or the oxidisation. 

Oh yeah, then put on some old 3D printed prototypes to dress it up a little and put it on the stand I made a last year.  Never thought it would be so handy!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: datadavid on Aug 25, 2017, 07:17:37
Is it even physically possible to get 30hp out of these? Staying tuned..
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: canyoncarver on Aug 25, 2017, 12:24:59
I'm in. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Aug 28, 2017, 17:57:30
Is it even physically possible to get 30hp out of these? Staying tuned..

Physically possible, absolutely. Technically possible, maybe.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Alex jb on Aug 29, 2017, 09:24:31
Physically possible, absolutely. Technically possible, maybe.
Isn't it the other way round?

Either way we want to see you try :)


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Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: CrabsAndCylinders on Aug 29, 2017, 14:03:55
Subscribed!  :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Aug 29, 2017, 14:23:41
Isn't it the other way round?

Either way we want to see you try :)


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My point is that the potential exists, but does the technical know how in this specific case exist? Maybe, maybe not.

I'm not OP though, so I'm not building it.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Alex jb on Aug 29, 2017, 16:34:22
Ok, gotcha.
I think so too.
I buying a Honda 250 twin motor to tear down make some mods and if it works out, heading for the ton too.


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Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: jpmobius on Aug 29, 2017, 17:56:14
Aerodynamics will be of critical importance with this much power to attain 100 mph.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 29, 2017, 18:15:12
Is it even physically possible to get 30hp out of these? Staying tuned..

Dunno man, but will sure as hell try.  From this research I have done, I will be going down the path of many small improvements to make a well tuned whole, rather than one or two drastic changes.  I'll be working a lot on lightening the entire valve train - with the intention of coping with more cam and lifting the rpm ceiling 1000rpm so it pulls to 10,000.  Will increase cc's and compression as well.  More will be revolved along the way!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 29, 2017, 18:17:12
Aerodynamics will be of critical importance with this much power to attain 100 mph.

Absolutely.  This will actually be more crucial than weight reduction and outright power.

That being said, I would like to try with minimal aero stuff.  At this early stage, I am hoping a good body position (clip-ons, rear sets, tank hugging) plus a small headlight faring (to throw a little wind over my helmet) might do.  But it will require testing.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 30, 2017, 18:09:04
I think I shared this resource on the other thread but here it is again:  http://www.klemmvintage.com/bighorntech.htm

Yes it is a 350cc 2 stoke, but the chassis - suspension and brake set ups are very interesting I have taken a lot of inspiration from what they have done.  I will be doing similar stuff  :)

I also purchased Tony Foales Handling and Chassis Design pdf.  It is super dense.  And a pretty hard read I thought.  I have picked up a few key points but otherwise, will not be going into extreme details like in there.  https://www.tonyfoale.com

I do know what rake and trail I would like and what ride height/eye to eye rear suspension I would like though.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 30, 2017, 18:11:41
I did some quick research and it seems like 30hp should get 160kph.  Some pretty nifty 250cc Ducati singles have done it!  http://www.motorcyclespecs.co.za/model/Classic%20Racers/moto_morini_250_gran_premio_1964.htm

Given, that particular model had a fairing, BUT could reach 140mph...
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 10, 2017, 06:11:57
I'll be doing a kickstart conversion on this bike too.  But many people just add it and have it as a compliment to the electric start.  I will be removing not only the starter, but also the many internal parts necessary to make it all work.  Some of these are even rotating mass = power sappers. 

I did a little exercise where I collected all the parts from the two different assemblies (from a spare engine I have) and weighed the two set ups.  The total weight savings will be around 2.5kg.  And that is just in the engine!  Then if I were to include the fact that the battery will be able to be half the size as well, there will be a few hundred grams extra savings there too.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Alex jb on Sep 10, 2017, 10:33:52
Thorough work!

If you are re-wiring then you could dump the e-start wiring and swap the hand control for one without button, it all helps!




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Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 11, 2017, 01:26:37
Thorough work!

If you are re-wiring then you could dump the e-start wiring and swap the hand control for one without button, it all helps!


Good point!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: datadavid on Sep 11, 2017, 07:21:26
Dont install the kicker, start it with a roller!
Title: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Alex jb on Sep 11, 2017, 11:51:37
Dont install the kicker, start it with a roller!
That's a man in a van following you to Starbucks to re-start you after your mochachocachino?! 


Joking aside, old Skool privateers used to bump start their bikes to dump the kick start shaft didn't they?


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Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 11, 2017, 17:12:18
Haha, yes, considered having it bump start only actually.  But with previous experience bump starting a high comp thumper (on my own), no thanks.  I'll keep some small practicalities on the bike  ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: CrabsAndCylinders on Sep 11, 2017, 17:58:43
Dont install the kicker, start it with a roller!

I did that on a couple bikes, it was fun and cool, I thought, except when stalling going up a steep hill during rush hour.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 17, 2017, 10:44:52
It may sound like a boring start, and it isn't where a lot of other people start but perhaps should...  Tyre choice.

For this lightweight racer I will matching tyres to rims first.  Then re-lacing them to the stock hubs with the Jadus 18" stainless spoke sets.

The tyre of choice is the Avon road rider, for many reasons.  It is tried and true, can handle the speed and handles really well - from both reviews and personal experience with one up front on the other Jadus SR.

http://www.avon-tyres.co.uk/motorcycle/roadrider

The size of choice will be a 90/90-18 up front and a 100/90-18 at the rear - will be plenty wide enough for this kind of power and will keep things light (always good with less rotating mass).

This means that rim choice will be aluminium for light weight and a size 2.15"-18 rim for the front, 2.50"-18 for the rear.  Here are some guides I used:
https://ridewrightwheels.com/pages/motorcycle-tire-wheel-fitment-chart
https://www.scribd.com/doc/253007466/Motorcycle-Rim-Width-Tire-Size-Chart
http://dropbears.com/motorcycles/utilities/tyrerim.htm

So next pay check, wheels will be the first purchase. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: stroker crazy on Sep 17, 2017, 18:51:51
If you haven't already chosen the rims, you could try Morad TC:
http://www.central-wheel.co.uk/rims/morad_rim/morad_rim.html (http://www.central-wheel.co.uk/rims/morad_rim/morad_rim.html)

Crazy
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 18, 2017, 17:22:54
If you haven't already chosen the rims, you could try Morad TC:
http://www.central-wheel.co.uk/rims/morad_rim/morad_rim.html (http://www.central-wheel.co.uk/rims/morad_rim/morad_rim.html)

Crazy

Good advice, have used their services many times and been very satisfied.  But this time I will go with a Swedish supplier who manufacture their own spokes and are very helpful - and also local!  They are a reseller for Excel rims too, so will go with them this time.  Will report if any major difference in quality to the Morad's.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 22, 2017, 03:31:31
Figured I may as well introduce some of the planned engine mods (at this stage - can always change).  So far no plans to do much with the bottom end, it'll all be improving gas flow, capacity and compression.

_ Custom made high comp 77mm piston (263cc, retains stock sleeve, no case boring required) - piston already measured up and sent to Special Piston Services in Australia - they specialise in one offs and a re super friendly with a lot of experience:  http://www.specialpistonservices.com  will try raise cr from 8.9:1 to 9.5:1 or even 10:1 if we can work out a good dome.

_  Hot cam, the most aggressive profile, regrind by Tighecams in Australia: http://tighecams.com.au

_ Ported head to allow better airflow - or, to allow the cam to do its thing

_ Custom titanium intake valve, SS exhaust valve, both with narrower stems and both much lighter than stock - will maintain same valve size though (more on that later)

_ Valve seats custom made from NBC to wick away heat from the ti valve better

_ Bronze valve guides - also for better heat transfer to the head

_ Single beehive valve springs

_ Titanium keepers, seats and retainers

_ Lightened rockers and tappets

Then I'll be doing a few things on the intake and exhaust side too - as mentioned previously some kind of crank case ventilation scavenging system and probably a harmonic intake.

As an experiment, I already tried lightening some rockers I had from a spare engine.  Good and worth while result.  Especially becuase the weight shaved is at the points furthest from the fulcrum - where they 'weigh' the most to the valve train. Those small tabs at the end of the rocker are for the decomp lever on the XT and TT model engines and because the rocker is a symmetrical part, Yamaha have used it on the intake side as well - where it is not needed (where neither are needed in the case of the electric start SR).  I will be converting to kick yes, but am hoping with the right technique, won't need the decomp set up from the XT engine.

Hoping to lift the rpm ceiling to 10,000 by putting the whole valve train on a diet with the aforementioned mods  ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: killerx on Sep 26, 2017, 16:09:41
You should be able to drill some holes in the webbing of the rockers.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 27, 2017, 03:13:54
You should be able to drill some holes in the webbing of the rockers.

Thanks man, this is the kinda advice/encouragment I was looking for  ;D  I am so sure I saw a great post about someone doing just that over on a Yamaha quad forum, but can't seem to find it now.  The only gains through this method though would be smaller holes right out towards the ends of the rocker.  Because drilling holes close to the fulcrum may make it lighter, but won't do anything for lightening the load on the cam or the valve spring.  Worth investigating on these scrap rockers though for sure!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: jpmobius on Sep 27, 2017, 11:01:41
Reducing weight is almost always a good thing as long as strength is not compromised.  However, it is worth keeping in mind your end goal.  What do you achieve?  Do you have in mind increasing safe operating rpm?  Generally higher revs make possible higher output.  Or do you plan on more aggressive cam profiles which will increase valve train accelerations? (same consequences valve train wise as increased rpm) Valve trains are often the limiting problem in output because the natural frequency of the springs needed to control the valve train components becomes too close to the engine rpm.  Drop a spring on the floor and it will "ring" or oscillate for a bit at its natural frequency.  If you "excite" it by driving it to this natural rate (or a harmonic of the natural rate) it will try to continue this rate of oscillation instead of following the camshafts intent.  Commonly called valve float and can be very destructive.  The solution is to require a lighter spring (or stiffer)(lighter meaning lower in mass in this context) that has a higher natural frequency so as not to be excited by the available rpm.  A lighter spring  will of course require lighter valve train parts.  Valves, pushrods, lifters, spring retainers, etc all move (mostly) linearly so simply making them lighter overall works toward this goal.  Rocker arms on the other hand rotate, so how you lighten them is less straight forward.  Mass at the center of rotation is of little concern as it moves very little, where mass at the end of the arm(s) is very important.  However, loads on the arm(s) generally become higher with stiffer springs and/or increased rpm, so one should be careful when lightening these parts so as not to compromise the beam strength of the arm.  Likely you would prefer a stronger rocker than a lighter rocker - which is not to say you still don't want the lightest you can get!  Anyway, the point is to be careful and thoughtful when altering your parts.  I'd say the lightening you have done so far has no down side, but potentially reducing the beam strength will provide negligible gains at best and potentially unnecessary troubles.  Having your valve train disassemble itself at max revs can be unpleasant!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 27, 2017, 14:08:47
Thanks for the inout jp!  I'll refer you to Reply #34 in this thread - just a few posts up on this page.  There I state all the engine mods I plan on doing with all the goals and some of the reasons.  Yes, lift the rpm ceiling to 10,000 rpm by putting the whole valve train on a diet (hence the whole rocker arm exercise) and using modern beehive valve springs - to avoid many of the problems you mention. 

Good point about the rocker mods though, this was my gut feeling...  Further mods might risk strength or may even result in flex at high rpm?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Oct 09, 2017, 14:45:24
Over the weekend I managed to start the tear down of the top end and do a bit of a measure up.  I wanted to know the exact weight of the piston assembly so we have a baseline for the new big bore piston.  I hope that with new methods, we can achieve a bigger piston with the same weight as this one so that the balance of the engine (both the primary balance for the crankshaft and the secondary from the balancer shaft) remains the same - so not to effect the vibration levels.  If this cannot be achieved, we will taper bore the piston wrist pin to get the weight back to stock.

Then the piston producer wanted to know valve angle and wanted me to mark the valve centres on the piston so he has a reference for machining out the valve clearance pockets.  The valve angles in the photos don't show up very accurate because of the perspective, but they were both 115 degrees.

I also measured the compressed height of a used head gasket and the deck height.  Deck height seems to be zero...  So just relies on valve to piston clearance and the clearance from the head gasket height.  Eventually I will cc the head and add this to the volume of the compressed gasket.  Then I will be able to get an exact compression ratio and be able to calculate and predict a new compression ratio with the new piston and the new swept volume.

The head volume is listed in the manual as 30.4cm3, head gasket thickness as 1mm (which is correct for a compressed one) and compression ratio as 8.9:1 (for the 239cc versions) and I have no reason not to believe this, but I want to measure it anyway.  I will also use that compression ratio and these listed numbers to reverse calculate the head and gasket volume just to double check my numbers and see if there are any differences.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Oct 18, 2017, 17:32:29
Tonight I managed to cc both the head and the piston dome.  These methods are pretty common practice but are usually done in a much more controlled, accurate way with proper equipment!  This was sort of a hack job to see if Yamaha were correct in the manual, where they state that the head volume is 30.4cc - which I didn't really understand, it just didn't add up in my calculations.  But then, after all the measuring and math, it turns out that the stated figure is actually total volume at TDC - taking into account the head volume, the gasket volume and the piston dome volume!

My rough measurements (all are written on the calculations sheet) all added to a volume at TDC of 31.7cc which is 1.3cc off what the manual says.  I was therefor happy to say that Yamaha are most likely correct and I am a little off haha, so will use this figure.  But good to know I was in the ball park. 

I calculated backwards for the different engine releases as well to double check the numbers - which added up.

With this number, I was able to calculate a new, predicted CR with the 77mm piston...  Which will roughly be 9.6:1 for a 9% increase over stock.  Is that enough?  Would 10:1 be better?  Imma look into it a little more.

In any case, I have many options to increase comp a little.  But the two most practical would be a slightly thinner solid copper gasket (will need a custom copper gasket anyway for the custom piston dims, so may as well be a little thinner) or to shave a little off the head.  Just by reducing compressed head gasket volume or actual head volume 2cc, the CR will be up to 10:1  ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Oct 18, 2017, 17:37:25
Here is a great post by a guy who did this process properly and accurately:  http://skrunkwerks.com/skrunk/measuring-compression-ratio-method-1/

Nicely documented too!

Just a little background perhaps for those CR numbers...  The North American SR was in fact a proper 250cc bike - displacing 249cc.  So with a TDC volume of 30.4 it gave a CR of 9.19, or as the specs round to, 9.2   Then all the other 239cc SR models have a CR of 8.8618, or as rounded to in the specs, 8.9  ;)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Eleganten on Nov 29, 2017, 20:52:23
This is going to be exciting to follow! Done by spring?


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Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 30, 2017, 14:59:35
This is going to be exciting to follow! Done by spring?


That's the plan!  But feels a little optimistic at this stage  :-\

Sorry for the lack of updates.  Not so much work has been done, but a shite load of research and things are set in motion.  Lot's of tech posts to come about the engine work  ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 10, 2017, 07:16:02
Finally saved the dough to buy the rims and the tires I mentioned.  Already have the spoke sets in stock so that part was easy!  Now can't decide if I should just build the wheels or if I should try make an instructional video on how to do it.  Feels like there are plenty on Youtube already?  But maybe good to have one specific to the SR?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Dec 10, 2017, 14:50:32
I assume you're going with the same 16" size as your previous build (that the spoke kit was made for)?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 10, 2017, 17:43:07
I assume you're going with the same 16" size as your previous build (that the spoke kit was made for)?

I actually had one off spoke sets custom made for those 16'' wheels - for the look I was going for.  Pretty idiotic of me to build a bike with 16" wheels, then not offer that option to customers.  I just figured most people would want either the scrambler or cafe racer look with these bikes - so I made the spoke kits for 18" - the spokes actually convert the standard 16" rear wheel to 18". 

In all honesty, and after comparing bikes, the way they ride, handle and feel, a good tyre on an 18" rim is much better than the 16's.  There is just too much tyre on there - rubber = heavy = slower acceleration = slower steering as well.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: CrabsAndCylinders on Dec 10, 2017, 18:02:57
A lot of guys over-tire their bikes to get the looks they want.  I think it just looks like bad engineering.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 16, 2017, 09:41:33
When pulling the head and barrel I noticed some pretty serious wear on the conrod small end and piston pin.  Piston pin = no problem, getting replaced anyways.  Conrod, kind of a bastard.  And with the planned mods, it doesn't make sense not to have a strong bottom end.  So I pulled her apart and will replace the crank pin, roller cage bearing, con rod and main bearings either side.  Tranny seems sweet and other bearings and seals are all good.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Pete12 on Dec 16, 2017, 18:22:07
Following this thread with a lot of interest, you're certainly analytical in your approach, very impressive.
I know that you really know your stuff with these little motors, but as you are chasing horsepower have you given any thought to removing the balancer shaft and then rebalancing the crank accordingly? Apologies if you've already covered this.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: hooligan998 on Dec 17, 2017, 01:30:54
Great info in this thread.  In.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 18, 2017, 17:14:08
Following this thread with a lot of interest, you're certainly analytical in your approach, very impressive.
I know that you really know your stuff with these little motors, but as you are chasing horsepower have you given any thought to removing the balancer shaft and then rebalancing the crank accordingly? Apologies if you've already covered this.

No, not covered yet and very good point, glad you brought it up.  I did look into this and read up on it.  Basically, vibration is a horsepower sapper.  Plus it is incredibly destructive on engine components.  I could have balanced the crank shaft with the new piston, but you can only balance for first order vibrations in a certain rpm range - say It was balanced for 10,000rpm, it would be horrible through the rest of the range.  I would still like a smooth spread of power through the rpm range.  Most modern 4 stroke singles (if not all?) have a balancer shaft, and those engineers are chasing power too.  It's just better to get gains else where.  Like for example by removing the electric start starter clutch, sprocket and chain, I will be removing a lot of rotational mass right there  :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: stroker crazy on Dec 18, 2017, 23:46:34
vibration is a horsepower sapper.

It also makes a machine unpleasant and tiring to ride.

Crazy

Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 19, 2017, 13:31:09
Here are the items I will do away with.  I will also have the crank either welded or plugged at these holes - the oil delivery to the starter clutch will no longer be needed, so they can be blocked off (will double and triple check this).  When taking apart the engine I cable tie assemblies together in the order they came off and then place them in ziplock bags.  Along with a bunch of photos too!  I also take photos of any special orientations or bolts that are longer than usual - to remember their placings.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 25, 2017, 13:15:54
Merry Xmas all, hope you had a good one.  I was pretty stoked because the custom piston I ordered arrived the day before the weekend.  More about that later.

I have thought through (checked and double checked) the starter gear thing.  I have decided I will not be blocking any oiling galleys. The centre part of the gear rotates on a bushing.  The bushing has oiling holes very similar to other parts in the engine - the small end, the rocker arms, the clutch basket etc.  This rotates on a plain machined bearing inside the starter gear - it even has golf ball drilling dimples to encourage better oil retention.  On each side of this starter gear are some slots/details that indicate oil distribution.  So I decided to retain it so that the other engine components around it - mostly the drive clutch drive gear and the counter balancer drive gear, receive oil the way they are supposed to.  However, because not using the actual gear, I cut that part of it off and will have it turned down on a lathe to match the outer diameter of the core.  This will make sure it is balanced - don't want any minute wobbling things at high rpm!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 25, 2017, 13:18:21
And on a completely different note, I reluctantly took on a commissioned build for a Danish customer.  I am now super stoked about it and I am glad he convinced me to take it on - it'll be fun.  But this adds another distraction to this project!  If you're interested, keep up with the build on Instagram and I'll keep posting progress there.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 27, 2017, 16:32:29
And here is the awesome custom piston from http://www.specialpistonservices.com in Australia.  I went to them because of their reputation and ability to produce one offs.  Plus they were great to deal with - Colin has a wealth of knowledge and is very friendly to have contact with.  They have stock of many different ring sizes and this sort of determines their piston diameter capabilities/offering.  In this case, it was a 77mm (3.5mm dia increase from stock) piston which equates to 263cc, or roughly a 10% displacement and compression increase.  It weighs in at about 330g's (without the packaging) which is roughly 10g (3%) heavier than stock.  I think this will be fine and hopefully the balancer shaft will take up the diff/vibes.

I have touched on this previously but will mention it again here because I am getting a tonne of questions on social media about it...  People ask 'why not use a warrior piston'?!  Or, why not go big and bore up the crankcases?  Almost every piece of engine tuning literature I have read advises against any one big change to the engine without compensating in other areas.  The engine will work much better as a package if each components is improved slightly and incrementally.  So, a bit more displacement, a bit more comp, a bit more cam (both duration and lift), a few more rpm (lighter valve train), a bit better flowing head, a bit better exhaust, intake etc etc.  Using a stock warrior piston requires both a crank case bore plus a new liner and increase displacement by a whopping 30% - making the engine way out of balance not just in respects to engine vibrations, but also the ability of the other components - how could you expect the stock SR head to flow 30% more air to match that new piston area?  And the crank to cope with that extra weight?  Although, these are just my interpretations and my decided direction.  I might end up being very wrong come testing  ;D



Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: jpmobius on Dec 27, 2017, 20:05:44
You are headed in the right direction!  Hold your course!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 31, 2017, 09:59:37
I have now packed up the items that will be taken to the engine rebuilders.  I will have the crank rebuilt with new components and have the SR sleeve bored up to match the piston.  Should I provide the piston clearance spec or will they have a good guide for that based on bore, cylinder construction, piston and sleeve material and the fact that it's air cooled?  The workshop manual has a spec of 0.035 - 0.055mm.  Is this good?

Hope you all have a great New Years! 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Pete12 on Jan 01, 2018, 05:13:29
Special Piston Services should be able to recommend the ideal piston to bore clearance based on the piston makeup.
This project is getting very interesting.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Jan 02, 2018, 06:38:41
Stock piston to cylinder clearances sound VERY small too me.

With regards to your upper conrod eye failure:
a) are you sure your oilsupply is good (or was the engine perhaps in a rather bad state initially)
b) have you noticed any detonation? You should see pinholes on the cylinder head and/or piston.

Especially detonation is a real killer on the small end as the pressure in the combustion chamber will go up in a rather uncontrolled fashion. I do like a bit of good old fashioned engine tuning like that...

With regards to why not a Warrior-Piston: 30% displacement increase shouldn't be a problem and in connection with the right cam the same goes for flow in the cylinder head. Truth be told, if Yamaha had built a 300cc version, that's probably all they would have done to it. Are you planning on welding up the combustion chamber to improve squish and speed up the combustion?

Cheers,
Greg
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 03, 2018, 13:34:22
Yepp, Special Piston Services came back with a recommended spec:  'CLEARANCE  = .0032Ē @ 23 MM BELOW OIL CONTROL RING you could perhaps try slightly less maybe .0025 min'

Anyone know why an Australian guy/company uses inches for bore measurement?  Then mm for measurement position?  .0032Ē = .08128mm, .0025" = 0.0635mm

So yeah, good call der nanno, the stock clearances are probs much too tight.  Will go with the recommendation from the piston manufacturer.

With regards to the conrod small end wear, I am positive oil delivery was good, I checked this with the check bolt and even connected in a low pressure oil gauge and got expected readings.  Not sure about detonation - no signs of it at all.  But an interesting point if this wear is not usual after 40,000kms, perhaps there was another failure elsewhere in the engine?  All other components look good and the oil did not show any weird debris.  When I bought the bike 2 years ago and changed the oil then, the valves were super loose and the oil was very dirty, so I suspect poor maintenance would have contributed. 

No plans to mess with the combustion chamber.  If I were building a race engine and it was my 10th engine build and I was trying to extract every last pinch of power from the engine I might.  But it would be too hit and miss I think - a bit of a black art if you ask me.  Looking at the chamber design it is set up like a modern swirl head so I hope it'll get a good burn rate with the new mods. 

Nice turbo build btw, great you found a carbon seal version for the draw thru!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Pete12 on Jan 03, 2018, 17:47:27
Anyone know why an Australian guy/company uses inches for bore measurement?  Then mm for measurement?
I'm Aussie and I agree it's odd but it's an old school industry standard. Bore and stroke generally measured in mm but clearances/interferences etc. generally given in inches. Never really thought about it until you mentioned it but it would be confusing for someone from outside. We haven't always been metric and a lot of people, myself included, were taught both systems.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Jan 05, 2018, 07:01:07
I'd say a conrod this worn has either done rather 140.000km or as you mentioned suffered a very hard life with long overdrawn  oil-chainge intervalls. Maybe you would want to look into the slude trap inside the crank, if that has filled up with a lot of debris, it might restrict the amount of oil coming out of it.

Thx, finding that turbo was a bit of a lucky shot. Even luckier me found a nice (tiny) supercharger and I'll go down that route during the 2018 season. I'll open a thread, when there's a little more time on the engine I am currently building for my everyday steed, where I play around A LOT with combustion-chamber reshaping.

And yes, mixing imperial and metric numbers is one of those things you find in lot of (originally) imperial countries.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: datadavid on Jan 07, 2018, 03:13:19
I'm Aussie and I agree it's odd but it's an old school industry standard. Bore and stroke generally measured in mm but clearances/interferences etc. generally given in inches. Never really thought about it until you mentioned it but it would be confusing for someone from outside. We haven't always been metric and a lot of people, myself included, were taught both systems.
Its because of the finer increments of 1/1000 inch than 1/100mm i think, but what do i know, im a welder! those measurements are too fine for me..
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 07, 2018, 13:12:06
Yeah it's interesting with the imperial thing.  Both my parents grew up with that system in New Zealand and remeber when the change came through the education system.  I think it is a legacy thing from the hot rodding industry in the US - it's just continued to be that with bore and stroke.  But good point about the finer increments david! 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Jan 08, 2018, 02:33:47
Its because of the finer increments of 1/1000 inch than 1/100mm

1/1000" is actually 2.54x 1/100mm, so it's in fact 2.54 times less accurate ;-)

(But we're officially splitting fractions of hairs...  ;D )
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: datadavid on Jan 08, 2018, 02:37:21
1/1000" is actually 2.54x 1/100mm, so it's in fact 2.54 times less accurate ;-)

(But we're officially splitting fractions of hairs...  ;D )
Tell the british that! they promised they will convert to metric though. Inch by inch!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: CrabsAndCylinders on Jan 08, 2018, 15:10:49
Metric is better.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: hooligan998 on Jan 09, 2018, 00:51:54
Its because of the finer increments of 1/1000 inch than 1/100mm i think, but what do i know, im a welder! those measurements are too fine for me..

1/1000" = .001"
1/100mm = 0.000393701"

Which is finer?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: datadavid on Jan 09, 2018, 01:01:18
1/1000" = .001"
1/100mm = 0.000393701"

Which is finer?
Did you bother to read what i wrote?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Jan 09, 2018, 03:46:21
0.035 - 0.055mm.  Is this good?

I've had another good long thought on the subject... It really depends on the bore and material of your piston. Is the new one forged as well or is it cast? If it's forged, you definitely have to go up with the tolerances and gutt-feeling tells me, around the 0.07mm to 0.08mm clearance is roughly 1/100 of the bore or one percent differential expansion due to dissimilar materials of piston and cylinder/liner in the hottest area of the piston and should be alright for a forged piston. If it actually is a cast piston, going below one percent will prolong piston life dramatically and aiming for the higher end of the range will probably just do you fine. Maybe being a bit more gentle on the first hundred kilometres might be advisable anyhow.

Cheers,
Greg
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: hooligan998 on Jan 10, 2018, 00:58:44
Did you bother to read what i wrote?

I had to read?  WTF is this?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: datadavid on Jan 10, 2018, 02:49:52
I had to read?  WTF is this?
It was a bit of a joke. Been using both imperial and metric for 15 years so no need to try and lecture. Thanks.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: themotoworks on Jan 10, 2018, 07:38:16
Yepp, Special Piston Services came back with a recommended spec:  'CLEARANCE  = .0032Ē @ 23 MM BELOW OIL CONTROL RING you could perhaps try slightly less maybe .0025 min'

Anyone know why an Australian guy/company uses inches for bore measurement?  Then mm for measurement position?  .0032Ē = .08128mm, .0025" = 0.0635mm


maybe their bore gauge is in inches :)  that and I think they toy a lot with american engines down that way, or at least if australia is anything like I learned from mad max, they do
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: stroker crazy on Jan 10, 2018, 08:47:41
if australia is anything like I learned from mad max Ö

Mad Max is actually a documentary!

Crazy
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: CrabsAndCylinders on Jan 10, 2018, 17:10:30
Mad Max is actually a documentary!

Crazy

Ha ha :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 10, 2018, 18:24:52
I've had another good long thought on the subject... It really depends on the bore and material of your piston. Is the new one forged as well or is it cast? If it's forged, you definitely have to go up with the tolerances and gutt-feeling tells me, around the 0.07mm to 0.08mm clearance is roughly 1/100 of the bore or one percent differential expansion due to dissimilar materials of piston and cylinder/liner in the hottest area of the piston and should be alright for a forged piston. If it actually is a cast piston, going below one percent will prolong piston life dramatically and aiming for the higher end of the range will probably just do you fine. Maybe being a bit more gentle on the first hundred kilometres might be advisable anyhow.

Cheers,
Greg

Thanks Greg.  Barrel is cast aluminium with a cast iron sleeve.  Piston is a forged blank which is then machined to spec.  Those clearances you suggest are pretty much bang on (on the looser side) of what SPS suggested - I reckon 0.07mm will do the trick.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 10, 2018, 18:29:51
Mad Max is actually a documentary!

Crazy

Hahahaha  ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 10, 2018, 18:32:09
Dropping the electric starter I need to block the gaping hole in the left crank case.  Start with a few measurements and a sketch, into CAD, a couple prototypes later to dial in the hole positions, then onto a drawing to send to the machinist :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: hooligan998 on Jan 11, 2018, 00:49:36
It was a bit of a joke. Been using both imperial and metric for 15 years so no need to try and lecture. Thanks.

I wasn't really lecturing, so if it came across that way, my bad.  Maybe I missed the point of your post.  I really wasn't trying to piss you off.  I've been using both for longer than that, hence the reason I posted it.

We good?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Pete12 on Jan 11, 2018, 08:45:23
Dropping the electric starter I need to block the gaping hole in the left crank case.  Start with a few measurements and a sketch, into CAD, a couple prototypes later to dial in the hole positions, then onto a drawing to send to the machinist :)
Nice work, looking forward to seeing the finished article.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 22, 2018, 01:29:31
Printed a final prototype on a slightly more accurate printer (at work) along with another prototype for the tacho/speedo drive plug and the ignition relocation bracket I have been working on.  Will try get the drawings for these done today ready for quotation requests.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 04, 2018, 10:23:06
A few updates...  I have been visiting the folks for a couple of weeks in Aus.  While I was there, my old man bought a project SR!  So cool.  He'll make himself a bit of a custom with Jadus parts and using the install vids I have done for youtube.  I also managed to salvage an old project.  I kept all the good bits - gave half to him (the big thing being the tricked out wheels) and kept half for my projects, then threw the rest.  I managed to recover a nice engine, a swing arm, some fork legs, rear sets, clip ons, carb, triple tree, mojave tank and a few other bits and pieces.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 05, 2018, 14:21:45
Been working on drawing up the geometry for a custom copper head gasket too.  A bit of fiddling in CAD and prototypes to get the hole positions correct!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Feb 05, 2018, 14:25:18
Put it on a flat bed scanner, insert the image into CAD, trace the image. Boom! I had to do this for a base gasket.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 05, 2018, 15:52:02
Put it on a flat bed scanner, insert the image into CAD, trace the image. Boom! I had to do this for a base gasket.

Imma do that!  Thanks!  Rather stupid of me not to think of that...   :o
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 07, 2018, 15:58:49
Bought a whole bunch of NOS parts from cmsnl a couple weeks ago.  Use them a lot actually - real good service too. 

https://www.cmsnl.com
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 12, 2018, 13:39:39
Just as I am giving praise to cmsnl they send me the wrong part!  I got a rocker from an SR500 I think!  The other one was correct which was weird.  Still pretty awesome customer service though - they didn't require me to return the wrong part and send the correct part free of charge.  No biggie.  However this little mistake sparked a wider investigation into the SR250's rockers...  More to come.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 12, 2018, 13:59:18
At some point between 1980 and 1982 (I think around then) the rockers were upgraded to be the ones used on the 350 quad engines - they are the same part.  The difference is that the original part is a cast item with a nitride hardened surface on the cam contact pad.  Whereas the new rockers/the quad rockers have a (through?) hardened pad on them as a separate part.  Another difference is the tappet screw and nut.  The original has an M6 x 0.75 thread while the replacement part has an M7 x 0.75 thread (first time I have encountered this).  This is why when you buy a new rocker, it comes as a set including the tappet and nut - because obviously these particular pieces are not interchangeable any more. Check out the photos for the differences.

I suspect there were either some wear issues or Yamaha wanted to consolidate parts across similar models.  The wear would have been on the cam and the rocker pads obviously, but I also suspect wear on the tappets and the valve stems was also an issue - as I am sure many of you have seen.  So going up a millimetre in diameter for increased contact surface area on the valve stem (up to M7) might have helped that.

There is also some good information on the Kedo site and other sites about the incompatibility of the different cams and rocker versions - looks like it was the same thing for the rockers in the SR500.  I am pretty sure though that it is no problem to run either rocker with an old cam, but not ok to run old rockers with any new cam?  I deduce that the new cams are harder and therefor the old rockers are not up to the job?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Feb 15, 2018, 05:30:16
As an ex-SR500 rider, rockers, rockershafts and cams are a huge problem with these on higher mileage bikes, because the oil-supply to the head is a bit of an issue. That being said, the hardpad-rockers are good to be used with all cams. The older chromed pad rockers do have a central oiling port in the center of the pad, which can (and will) ultimately leave a little ridge on a used cam. If your new cam is nitride-treated, get some 2000-3000 grit sandpaper oil it generously and run the sandpaper over the cam-surface until it brightens up a bit. This will take off the sharp edges of the nitride coating and allow you to run older style softer rockers on SR-cams. (Generally the same rules should apply with the 250, but I only have personal experience on the 500, especially with reground and nitrided cams...)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: datadavid on Feb 15, 2018, 16:55:57
Looks like a stellite pad on the late rockers to me, quite like old triumph cam followers.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 24, 2018, 11:49:24
That being said, the hardpad-rockers are good to be used with all cams.

Cool, I figured that was the case.

Cheers for the input guys!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 24, 2018, 11:53:10
Got the prototypes machined aluminium parts back from the machinist.  They look amazing.  I think I'll bring the tach plug into production - because it fits other engines too I think, plus it fits unused speedo drive holes in wheels (if an electric speedo is used).  And will probably bring the ignition bracket into production as well.  Not so sure about the electric start plug.  Feels like not many people follow through with the conversion to this level...
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Feb 25, 2018, 13:38:23
I think the tach-plug is available from Kedo for the SR/XTs and is dead cheap, so you may want to check the market first before spending any money on having a few made up for resale. :-/
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 26, 2018, 16:15:59
I think the tach-plug is available from Kedo for the SR/XTs and is dead cheap, so you may want to check the market first before spending any money on having a few made up for resale. :-/

Thanks for the heads up!  I found a few different ones online actually.  Imma buy a couple of them and see if they are any different.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 01, 2018, 15:58:17
Here comes a bit of a dense post about valves and cam.  I know I have mentioned the plans previously, but here are some photos to go along with it.

I got really confused by some cam specs for the SR and XT engines (same same).  See attached the data sheets from the respective workshop manuals.  Then when I check out cam regrind websites - Web camshafts and Tighe camshafts for example, the numbers just don't seem to add up.  Nor do they when looking at specs advertised for the 350 quad engine cams.  The answer to the misunderstanding is net and gross cam lift - or affective cam lift at the valve - which equals a number multiplied by the rocker ratio.  Because the SR's rocker is a somewhat whacky shape, it was impossible to calculate a ratio on paper with measuring tools - especially if you are going to consider the dynamic movement it has at the tip of the tappet on the top of the valve.  So the best way to measure is to set the head up and measure true valve lift with a dial gauge and compare that to measured cam profile difference - from the base circle compared to the tip of the lift lobe across.

I managed to measure 9.1mm of lift on the exhaust valve and the cam on the exhaust lobe has 8.25mm of lift.  Which for my calculations gives a rocker ratio of 1.1:1  But this still doesn't add up when looking at the numbers on the websites...  I double checked and then checked with the Tighe cam as well, same ratio.  The info on the Tighe cams website states a rocker ratio of 1.3:1 but perhaps that is for the SR500 and not for the SR250?  Which would put the specs off?  Either way, there will be clearance for the valves to the piston at maximum lift because these cams are designed to work with the stock piston.  I gave up figuring that out.

I also attached a screen shot of a spreadsheet I made comparing a few different cams - to see what was suitable for this engine.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 01, 2018, 16:18:16
Now about the valves...  A few people have swapped out the SR valves for 350 quad valves - 2mm bigger in diameter for both intake and exhaust (see attached comparison).  I have decided not to do this because of the extra weight, plus I don't think the SR head can flow that much air.  I want to move those valves up and down faster (higher rpm) in a controlled manner without getting valve float or 'bounce'.  I also found an interesting table in the 4 stroke tuning book by Graham Bell about valve size and the different valves sizes of engines according to their cylinder capacity.  I concluded that the SR is already over valved, or has correctly sized valves for the power I am after - see attached a summary of relevant cylinder capacities I made.

I was also going to copy a lot of modern 4 stroke motocross bikes and have the intake valve (which is always slightly larger and subject to less heat than the exhaust valve) made in Ti and the exhaust valve in SS to cope with the heat and wear.  After speaking with Chris from Schumann Motor Works I have decided to go with both valves in SS, but reduce the stem from 7mm to 5.5mm - thereby reducing weight but maintaining reliable valve life.  Out of curiosity I did a quick CAD exercise where I modelled an SR valve and 'weighed' it as Ti with a 7mm stem, then as SS with a 5.5mm stem and they came up super close.  Although not too accurate specifying a material in a CAD program, it gives an indication.  At least the valves will be lighter than stock!  Also, by using SS for both, the valve seats in the head can just be reground rather than replaced (would need to be something else for the Ti valve).
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Mar 03, 2018, 03:54:55
Are you sure, the pads aren't worn on your SR250 rockers? Also you stated that there are multiple types (chromed and hardfaced) of rockers for the 250. Now add some manufacturing tolerances and then some optimistic round from the cam-manufacturer and you could quite easily end up with the differences.

Are there any off-the-shelf 5.5mm valve guides available? Personally I am no big fan of Ti-Valves in vehicles that may actually end up making some miles, mainly because wear and tear is a bit hard to monitor (for me). If you start lightening the valve train, I'd also have a look at the rockers. At least on SR500s they can be lightened a bit.

Oh and excuse my ignorance, but what kind of rev-limit do you have in mind with this engine?

I really like your approach of doing proper research, way too few people seem to do it like that, when building a bike.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 03, 2018, 06:36:34
About the rocker pads...  I actually did the measurements with both versions of the rockers and came up with the same results.  As with any good measurement, I took it several times then took the average - same for both.  I did this because I always thought this particular bike made slightly more power than the black one and I thought it might have had something to do with the rockers - if the ratio was slightly better, the valves would get a little more lift = a little more air fuel mixture = a little more power.  But this was not the case.  Goes to show how accurate the butt dyno is haha.

Not sure about the 5.5mm valve guides, probably is.  Thing is, Chris makes everything custom to each application anyway, so he'll turn some up in the right material and size.  Yeah, I am happy with the decision about SS instead of Ti.

Current power falls off at about 7800rpm but will rev to 9000rpm.  I basically want to be able to rev to 10000 and have power all the way up to 9500.  I think this is achievable with the weight loss program.

Yeah, will be lightening the rockers - I covered this a few pages back in the thread   :)

This amount of research is usually very unnecessary (unless rebuilding an engine to non stock spec) but I am treating it as an educational process and I am super passionate about it so it's all just really interesting to me!  I have read a few posts on your blog too, looks like you take a similar approach! 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 03, 2018, 10:02:05
The butt dyno is pure confirmation bias. Anybody who has ever worked with data acquisition knows this to be true.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 13, 2018, 19:42:15
While preparing and packing up the head to send away for machine work, I decided to see if I could remove the tach drive system entirely.  The answer is yes.  But then there is nothing for the tach-plug I have made to push up against and it sinks into the hole in the head too deep to form a seal.  So I put it back in!  It will not be driven anyway because the cam regrind I got was done on a non-tach drive cam (missing the worm gear drive).  Anyway, if anyone was curious, this is what the assembly looks like...
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Eleganten on Mar 14, 2018, 18:48:04
Why not just drill and thread a hole on the top side. Then make a aluminum plug with a flange and a plain hole? Worst outcome would be oil leakage in case the bolt unscrews and the plug comes off.

Hit me up if you want one done and Iíll squeeze it in at work.


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Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 15, 2018, 16:02:07
A custom plug could definitely be a solution!   You work with CNC machines?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 17, 2018, 12:34:43
A cool day for the project yesterday - I went in and picked up the parts from the machinist/engine refurbishing mob!

The rebuilt crank looks amazing, nice to know the bottom end is fresh and strong when I put extra stress on it.  He swapped out the bearing for a brand new one as well - this is a part Yamaha doesn't list on the spare parts program (rather it is a part of the crank half assembly), but he managed to source the correct one and replace it!  Woohoo.

The bored up cylinder looks really nice as well, finished with the typical cross hatch honing.  The guy said he shot for the middle of the suggested clearance tolerances and that came out at 0.075mm or something - pretty much what der_nanno suggested.  He also explained the difference in these tolerances vs the factory specs for the factory piston... Also what der_nanno mentioned a few pages back.  The stock piston is cast and expands less than a forged/machined piston like this new custom one is.  He also said that because of that, the engine might be a bit noisier than stock when it is cold - until the engine gets to temp and the piston expands and comes into it's working diameter spec.

The machined starter drive gear looks great too.  This actually ended up costing more than I thought - because it is hardened it couldn't just be turned down in a lathe with a bit, rather it needed to be ground down in the lathe with a grinding stone.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Mar 17, 2018, 20:33:14
I may admit that I am an engineer by trade...  ;)

Nice to see, that your engine is coming along nicely.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 18, 2018, 15:25:25
Might need to pick your brains for the next job...  Assembling the crankcases.  Which sealant do you recommend?  Yamabond #4?  I heard 3 bond is the same product/manufactures the Yamabond.  Anyone use anything else?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Eleganten on Mar 19, 2018, 08:55:37
A custom plug could definitely be a solution!   You work with CNC machines?

I got 3 of them at workHowever I would turn it manually in the lathe and mill since that would take way less time since our 5-axis ainít running at the moment.

Just send me a drawing and your address and Iíll try to sort it out for you.


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Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Mar 19, 2018, 11:25:59
Anyone use anything else?

I use Elring Dirko HT (red), with great success. Especially as it's a lot cheaper overhere and it comes off very easily with just a bit of Acetone. And a little bit goes a very long way, i.e. a tube will last you several engine cases.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 20, 2018, 17:21:20
Just send me a drawing and your address and Iíll try to sort it out for you.

I'll take you up on that!  I'll need to measure things up and design it first so it may take a while before I get there.  Cheers!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 20, 2018, 17:21:56
I use Elring Dirko HT (red), with great success. Especially as it's a lot cheaper overhere and it comes off very easily with just a bit of Acetone. And a little bit goes a very long way, i.e. a tube will last you several engine cases.

Awesome, thanks.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: datadavid on Apr 01, 2018, 14:23:40
This is nice!(https://uploads.tapatalk-cdn.com/20180401/e3f88d68dbe79ceb5060b9f363c1a234.jpg)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 05, 2018, 14:20:42
Haha, thanks!  I guess you got yerself a copy  :D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 05, 2018, 14:23:28
Been pretty quiet recently - been working on the custom for Lars.  Now it is finally complete though!  It came out pretty good for a 4month, 60 hour total (spare time after work) project.  Really happy it is complete and can now get back to this.  Lars was stoked too, which made the whole project sweet and well worthwhile.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Alex jb on Apr 06, 2018, 10:30:38
Like new!
Nice job.


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Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Apr 07, 2018, 04:12:45
Sweet lil' bike!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 07, 2018, 09:10:07
Thanks!

Now that the engine project is pretty much on track, or at least, things have been ordered and it is just a matter of doing the work, there is now time to focus on the chassis - wheels, frame, suspension etc.

The SR has notoriously poorly performing forks, so I have been focusing a bit on that first because it feels like that will be the most challenging.  I have done a lot of reading and have been trying to weed out the good information from the bad and trying to decide what mods to do and for what cost/benefit ratio.  Because eventually, if I come up with something good, it could be a nice product for all to have access to.

I have read a lot about the Race Tech cartridge emulators and they seem like the hot ticket for old RWU damper rod forks.  But they are pretty pricey and I am not sure many people would be that willing to go so deep into their forks.  I have also read through the Minton mods for forks for the XS650 and they seem like a good place to start - relatively small changes for good and cost effective results.  I think I will try and find some looser fork seals to reduce sticktion, experiment with fork oil weight and volume, and also preload - which would require either spacers or some special fork caps with preload adjusters.  For anyone interested, here is the Minton mods: http://www.650central.com/tech/mintonmods.htm

And here is good stuff about damper rod forks and the cartridge kits: http://www.racetech.com/page/title/Emulators-How%20They%20Work and here: https://www.youtube.com/watch?v=j3QYZEQoN_M

And I have listed the things that are adjustable on the fork.

Adjustable inputs:

Oil level
Oil viscosity
Preload on springs
Spring rate - single rate, double rate, progressive.  Also spring length vs spacer length.
Valve emulators - on top of damper rods, requiring destruction of the damper rods (in essence removing their original function)
Add air valves - for air fork function

The air fork function is what I am least familiar with.  I have a full-suss mountain bike with air shocks front and rear and adjust that every now and then, but still don't know why that method is chosen over others, or the advantages and disadvantages.  If someone can elaborate on this, I am all ears, but at this point, because it is least familiar to me, it is less likely something I will do.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Apr 07, 2018, 10:54:09
What size emulators would it need? They have to fit inside the springs and are usually the same OD as the top of the dampers rod.

I ask because there are other options than the RaceTechs, they don't have it patented or something. But you can't beat cartidges, the fundamentally improve the damping function.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Apr 07, 2018, 19:06:42
I know the Ricor Intiminators (different internal cartridge emulator) are real popular with V-Strom owners but I think the smallest version is still 39mm. Cogent Dynamics also has the Drop in Damper Cartridge (DDC) and fork springs but I don't know what sizes they have. If you want to retain the OEM 32mm fork tubes, there's not much more that can be done than a stronger spring (maybe custom or from a CB360/400) a fork brace (you already have that) and different weight oil. Front end swaps are doable, but would look funny if you did not use a spoked front wheel (unless you swapped both front and rear wheels), but using a front end with a disk brake adds a better braking dimension.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Apr 08, 2018, 16:09:20
YSS makes emulators, there are also Taiwanese knockoffs. I have tired the YSS, the RT's, and the knockoffs on my RD 350 (FZR600 forks). I prefer the knockoffs over all of them. That said, one of my long brewing projects has been to make a set of my own design, albeit highly derivative of the existing designs. There's not really a lot of room left of innovation with this type of damping arrangement, emulators pretty much top them out performance wise.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 11, 2018, 16:29:04
Thanks for the feedback and tips about other emulators.  Good to know.  Which measurement is important for the emulators to fit?  Is it the stanchion inner diameter, the spring diameter, or do I need to disassemble the forks and measure up the damper rod and get it's dimensions?

I have taken it upon myself to start designing an adjustable preload fork cap.  First things first, measure up the fork tubes, caps, c-ring, oring etc.  I have also ordered some custom stainless spacers for the black Jadus SR because I want to sell it and the forks are the only thing letting it down.  I ordered several 5mm thick spacers and will experiment with how much preload feels good.  Then I will use that as a basis for the adjustable ones.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Apr 11, 2018, 16:50:49
I think an adjustable preload cap would be a lot of work with very little benefit. Most preload devices are some sort of tube (usually PVC plastic) that partially compresses the spring. Cut the tube for the amount of preload you want. Some trial and error, but fairly easy and real cheap - but you lose suspension travel. To minimally improve the OEM forks you need to get the right springs for the expected rider/vehicle weight (the OEMs are typically undersprung). Correct weight springs means minimal need for preload. Then experiment with extension/compression circuits, bleed holes and fork oil weight.

To radically improve the forks you need larger tubes for stability at the triple trees - either upside down (real sturdy in the triple trees) or right-side up with a fork brace. Still need the right springs and probably need to experiment with bleed holes/oil weight - unless you swap-in a cartridge fork. Complete front end swap (with front disk brake) usually makes the most sense.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Apr 12, 2018, 11:47:44
The spring sits on top of the emulator and the emulator sits on top of the damper rod. Generally the emulator is the same OD as the spring. The emulator valve preload spring (the part that actually does the work) is inside the fork spring.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 14, 2018, 14:56:31
Ok well if the emulators sit like you say, I should order the 23.8mm YSS emulators and give them a crack (internal diam of SR forks is 23.95mm roughly).

After working on the forks on the black Jadus bike and the orange one, I would say preload would do a lot.  There is so much sag in the fork already!  I know that when you add preload you loose suspension travel.  But the SR already has 140mm, which by today's standards is excessive for a road bike.  I think if the result of a well sprung SR fork ended up being 100mm travel, it would be plenty. 

See that is the thing with those plastic PVC spacers, it is trial and error and if you cut too short there is no going back.  If I design the preload adjusters to have say 10mm preload in them already, they could have a further 30mm of adjustment travel and this would make a big difference.  Then if the ride ends up being too harsh or oversprung, the adjusters could be backed out a little.

I know all the other paths to improve the forks involve larger, stronger/stiffer fork tubes and front end swaps, but call me old fashion, I just think modern forks look downright silly on vintage bikes.  I know it's a fad right now and it is a taste thing, but the forks will always end up outperforming the bike.  Besides, how many SR owners would be prepared to do a front end swap?  Not many I think.  I had a guy contact me on insta wanting to sell me a custom set he had made from Cognito Moto for 1500USD for his project.  He of course had since abandoned the project and was looking to get some money back on the parts.  1500USD would get you an entire SR250!!!  Mental imho.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Rat_ranger on Apr 14, 2018, 16:58:34
Preload caps should be pretty simple to make.  I mean the xs650 had fork caps that allowed 3 different preload options. 

 As far as fork swaps, I think a bunch of people don't look at how much it'll cost in the end.  I mean its what $150 for a stem, $400 for a hub, whatever the forks cost you, maybe triple clamps.  Then there is the rim and spokes and lacing.  Even my extreme budget swap was about $700, that was making or modding parts and using scrap bin materials where I could. 

*edit* basic ones look pretty simple to me. https://www.economycycle.com/wp-content/uploads/2014/12/RDPreloadAdj2.jpg
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Apr 14, 2018, 18:13:07
Ok well if the emulators sit like you say, I should order the 23.8mm YSS emulators and give them a crack (internal diam of SR forks is 23.95mm roughly).
I think this is the most promising direction yet, as you already have the fork brace.

After working on the forks on the black Jadus bike and the orange one, I would say preload would do a lot.  There is so much sag in the fork already!  I know that when you add preload you loose suspension travel.  But the SR already has 140mm, which by today's standards is excessive for a road bike.  I think if the result of a well sprung SR fork ended up being 100mm travel, it would be plenty. 
I think I saved some info from CrazyPJ where he recommended Honda CB360/400F springs as they were a little loose for the Honda's 33mm forks and fit the SR250's 32mm (also mentioned XS250/400 springs). Probably could get custom springs wound but it would also be pricey.

See that is the thing with those plastic PVC spacers, it is trial and error and if you cut too short there is no going back.  If I design the preload adjusters to have say 10mm preload in them already, they could have a further 30mm of adjustment travel and this would make a big difference.  Then if the ride ends up being too harsh or oversprung, the adjusters could be backed out a little.
True, but PVC pipe is real cheap and easy to cut.

I know all the other paths to improve the forks involve larger, stronger/stiffer fork tubes and front end swaps, but call me old fashion, I just think modern forks look downright silly on vintage bikes.  I know it's a fad right now and it is a taste thing, but the forks will always end up outperforming the bike.  Besides, how many SR owners would be prepared to do a front end swap?  Not many I think.  I had a guy contact me on insta wanting to sell me a custom set he had made from Cognito Moto for 1500USD for his project.  He of course had since abandoned the project and was looking to get some money back on the parts.  1500USD would get you an entire SR250!!!  Mental imho.
Mental - agreed
Along this line, I know that Cosworth had a somewhat interesting fork mod that he swears by. I believe it is detailed in his SR250 Cafť Racer build.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 29, 2018, 04:54:36
Yes, I also think custom springs, or even progressive springs (available online) would be too pricey for this bike.  Yes, PVC is cheap - I actually got a message from a customer the other day to say he completely cut out the soft part of the SR spring (it is two stage rather than progressive) and replaced that with a spacer.  He had good results with that but needed to heat up the cut end of the spring, bend it over and then linish it flat to get a decent seat for the spacer to sit on.  I figure not every weekend mechanic has a blow torch and a linisher!  So I'll shelve that idea.

Yes, I have saved all the posts from Cosworth about his fork mods - they seemed to work really well.  I'll be using some of these ideas too.

Anyway, I received the prototype spacers I mentioned in a previous post.  I'll install them along with a little extra fork oil and see how that rides.

My latest idea is to somehow design the adjustable spacers to have a through hole in them when the preload adjuster is backed all the way out - so that you can remove and add fork oil with a small tube without removing the entire cap.  This then gives adjustment on the spring (with the preload adjuster) and on the dampening - more oil, less air in the fork, harsher damping, less oil, more air in the fork, softer damping.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 22, 2018, 04:27:05
I tested these spacers in the black Jadus bike along with 170cc (168 in manual) of 20W fork oil in each leg.  It improved the forks about 10%, barely noticeable.  I have tried 200cc in each fork leg in another SR and that seemed to help a little more - it probably didn't make the fork perform any better, just made it feel less mushy.

I am convinced that for this build, I will use emulators for improved damping and then spacers with adjustable preload for spring control.  However, I will cut out the soft part of the springs and replace with a long spacer.  The fork is just always going to be mushy with that first pathetic spring rate.

As for something I will be able to offer customers, that is a tougher one - it is a balance of cost vs benefit and ease of installation!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Pod70 on May 22, 2018, 12:27:58
Really following this with interest and I like your approach to upgrading the bike.

As you say the preload adjusters will just reduce the sag in the forks but not eliminate the mushiness in the forks, only stiffer springs will solve this.

I'm guessing the forks on the SR250 are 32mm which could open up the possibility of using RD250/350LC springs which given the racing heritage of these little bikes, springs should be readily available in a range of rates. As to what rate you require, I would guess you're looking at around 0.8kg/mm at a rough guess which Sonic Springs are listing for around $85 which I don't think is too bad. Add in the emulators and with a bit of setting up you will totally transform the bike
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on May 22, 2018, 13:51:54
Really following this with interest and I like your approach to upgrading the bike.

As you say the preload adjusters will just reduce the sag in the forks but not eliminate the mushiness in the forks, only stiffer springs will solve this.

I'm guessing the forks on the SR250 are 32mm which could open up the possibility of using RD250/350LC springs which given the racing heritage of these little bikes, springs should be readily available in a range of rates. As to what rate you require, I would guess you're looking at around 0.8kg/mm at a rough guess which Sonic Springs are listing for around $85 which I don't think is too bad. Add in the emulators and with a bit of setting up you will totally transform the bike
Yes, the SR250 forks are 32mm. But I thought the RD250/350LC forks are 34mm (E and F are 35mm)? Maybe their springs are loose like the Honda CB360/400? Maybe contact Sonic to see if their springs are less than the 23.95mm Jake measured?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Pod70 on May 23, 2018, 12:25:21
From the what I could find, the 80-83 model RD250/350 LC had 32mm forks - I certainly remember them being pretty spindly on mine all those years ago.. ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on May 23, 2018, 13:06:14
I think you may be correct - found this reference - https://hvccycle.net/yamaha-rd-specs/ (https://hvccycle.net/yamaha-rd-specs/) - that says the liquid-cooled (LC) RD350 had 32mm forks. I don't think the USA ever got that model (just the RZ350) and the air-cooled RD models (except for the RD200) look like they had 34mm forks.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 19, 2018, 07:50:05
Thanks for all the input guys.  I will be looking into these springs for sure.  I have a couple of old fork sets on their way to me from Australia so I can use them in the development of the spacers and spring specification.

This project is going much slower than I would like - mainly due to the fact that my day job has been much more demanding recently than I thought it would be, plus I am focusing on providing the best service I can for my customers and prioritizing that over these other projects. 

I have however managed to add a video showing how to service and rebuild the SR250 carb, plus written a blog post to compliment it.  I also created a bit of a jetting guide for SR250's with various intake and exhaust set ups - share for all and report your own feedback and results!  :D :D :D

https://www.youtube.com/watch?v=FKtTxoJAO8g&t=1294s

https://www.jadusmotorcycleparts.com/single-post/2018/05/17/Yamaha-SR250-carb-rebuild-maintenance-tuning

I am just as hungry as ever to get back into this project so hopefully when time becomes available it will be all on again!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jul 28, 2018, 07:51:47
Finally an update worth posting...  I got around to lacing up one of the wheels this week.  I am not sure how other people do it, funnily enough I have never watched a how to vid, but I have screwed up a few times and learnt some tricks by doing.  Now that I am more confident with the process (have done around 10 wheels I guess) I think I'll make a video how to do it.  Anyone have any good tips?  Ie good youtube videos or blog posts/articles other people have done? 

I also got that package from Australia.  Most relevant to this project are the forks...  Which I can begin dissecting and experimenting with ;D Yay!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Jul 28, 2018, 11:02:48
I assume the Excel wheels are for the weight reduction program. If so, how much weight did you lose over OEM, and did you use the OEM size or go more narrow to reduce rolling resistance?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jul 30, 2018, 05:04:37
I assume the Excel wheels are for the weight reduction program. If so, how much weight did you lose over OEM, and did you use the OEM size or go more narrow to reduce rolling resistance?

Exactly.  I will weigh an entire wheel assembly - old and new and compare once complete.  I expect weight savings to be 1-1.5kg for each wheel.  Because yes, I will be running less tyre than stock as well.  According to the rim size to tyre size charts, the stock SR rims are right on the edge of acceptable for the stock tyre sizes.  So I actually went with wider rims and narrower tyres (matching optimal sizes according to the charts) - I guess this lets the tyre perform better, or at least as the manufacturer intended.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: CrabsAndCylinders on Aug 02, 2018, 23:34:16
I think the alloy rims alone usually save about 2.5lbs and that is reciprocal weight!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 06, 2018, 12:41:17
I was really keen to do something fun with the project on the weekend.  Fun does not always equal the best for the project but it's a good way to keep yourself motivated and moving along.

Anyway many years ago I created a meticulous drill template for the drum brake covers/drum lever holders that I used on a project that was never finished (my Dad will get the wheels from it though!).  The template was created to allow the most drilled holes practical without messing with the structural integrity of the parts - missing all the cast details, bosses and ribs.  Which meant it needed to be scanned front and back and a pattern laid out to suit.

The process was pretty simple but time consuming.  Some might laugh at the effort but I think it looks cool and will give a special hand built touch to the bike.  I must admit, it is mostly for looks, but I weighed the parts before and after just for a laugh - a 50g weight savings!  Woohoo!  Haha.  Just gotta do that in 20 places and It'll be a kg savings total  ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Aug 06, 2018, 13:31:38
If you still have a bike with the OEM drums you could do a comparison test on braking performance improvements - especially fade.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Jimbonaut on Aug 06, 2018, 13:49:18
That looks great. Think I read somewhere that this effect is called drillium which is itself a cool word. Is there any issues with water getting in and affecting the shoes/drum?


Sent from my iPhone using DO THE TON
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: MiniatureNinja on Aug 06, 2018, 17:50:46
That looks great. Think I read somewhere that this effect is called drillium which is itself a cool word. Is there any issues with water getting in and affecting the shoes/drum?


Sent from my iPhone using DO THE TON

i've only ever seen "drillium" used in the bicycle world - but I mean really... we just attach spinning explosion powered heat generators to our two wheeled death machines
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Aug 06, 2018, 18:44:14
Weakening holes is what we always referred to them as in the race car world.

Nice work though, it looks good.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 10, 2018, 10:07:07
Weakening holes is what we always referred to them as in the race car world.

Nice work though, it looks good.

Haha Yes!  I have heard that too.  Gets pretty dicey if you start drilling up structural sheet metal in a car.  People can sometimes miss the fact that the sheet metal itself does a lot for the structural integrity and not just the main structural elements.

I think in this case there will not be too many extreme forces on the parts.  The only boss that could be under stress is the brake lever wire perch - but I will be replacing this with an alternative system anyways.

In response to @The Jimbonaut about water...  If this was going to be a daily rider I actually wouldn't do this.  It was quite a lot of work for very little weight loss and 'looks' and it will let more water and dust in, yes.  However, because this is pretty much a purpose built machine, I won't be riding it often and will only be out in the sunshine  ;) ;D

Also drillium, lol.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Aug 10, 2018, 12:44:14
You certainly have to pick and chose which places you weaken.

I've been meaning to model up the brake plate for my RD and then make some configuration for lightening it via CNC. The major benefit there is that I can pick and chose what gets removed and do so in fairly inorganic ways. Hopefully that would result in a lighter piece than just drilling holes but with less weakening. That's the idea anyways, and it's pretty far down on the list of things to do, I may never get to it.

In regards to the water issue, I doubt it's much of an issue. Drum brakes just aren't all that sensitive in my experience. My vintage Formuala Vee is drum brakes on all four corners and the braking character really doesn't change from wet to dry. Now when the axle seals leak it's a totally different story.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 11, 2018, 02:50:46
I have slowly chipped away at building up the wheels this week, or I should say truing.  I had built the rear wheel last week (but had not trued it) but then I decided to try and build the front wheel and film it.  What a nightmare.  It's really hard to instruct a complex process!  I ended up starting from scratch 3 times and the build itself took about 4 hours hahaha.  Then truing took at least an hour per wheel.  But it is just a time consuming process.  Very rewarding though!  I ended up getting both wheels to within 1mm lateral freeplay and 1-1.5mm axial (manual limits are 2mm).

Also, check out my makeshift truing stands!  This actually worked out really well because you don't need to measure or think about hub-rim offset, rather you can just measure from the edge of the rim to the forks/swing-arm and adjust it so it is centered. 

I'll get a shop to mount the rubber and balance the tyres  :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 22, 2018, 18:15:46
Managed to open up one of the old fork legs tonight.  I have done this a few times now and have sworn and grazed knuckles enough that I have found a couple tricks that make the process a bit easier - especially if you don't have an extra set of hands and especially if that damn thing is rusted solid(ish). 

Anyway, there is enough depth in the fork cap to drill and tap a hole about 15mm deep, so I do that first.  Then I hit the cap a little (downwards) to break it loose.  Then I ratchet down a socket on top of that and pry out the metal ring that holds it on place with a micro screwdriver.  I hate this damn ring, it is a nightmare to get out.  I am already looking at circlip alternatives for my own solution.  Then once the ring is removed, you can very carefully release the ratchet - with safety glasses on and no-one else (or thing) to harm in sight.  Sometimes it will just pop up, other times (like in this case) it will not - because of the rust build up.  This is where the threaded hole comes into play - you can screw in a bolt and bash upwards to get it out.  Pang!  Be careful  ;D

Now I can start experimenting with spring length, spacers, adjusters, emulators etc (all as discussed previously) without disturbing any of my other running SR's or dismantling this project's rolling chassis.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Aug 23, 2018, 03:55:43
Oh that looks familliar. I thought about using a safety clip instead of the wire in the past. (early XS750ies and Yamaha TR1s use the same setup)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 23, 2018, 12:43:36
Forgot to mention that I had already soaked the fork caps in penetrating oil for a few days and had applied heat to them with the heat gun a couple of cycles as well - this definitely helps.

Yeah der_nanno, total pain to work with.  I actually just ordered some stainless circlips in the correct dimensions.  My only hesitation is that the ring is hardened steel - which is extremely tough.  The circlips might be a bit soft for the job?  Maybe not, I'll try it out.  They may well be just fine - it is just a small line contact to hold it all together I don't think there is enough room for the circlip to deform, rather it will get sandwiched in a good way between the cap and the forks undercut. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Aug 24, 2018, 05:26:11
If anything, it might wear out the ridge, because the edges of a snap-ring are really sharp. Rounding them off with a file might be the right way to avoid this.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 30, 2018, 12:13:45
Last night I tried experimenting with the idea of getting the front brake cable to run parallel with the fork leg - so that the lever is at right angles.  This removes cable length and bends in the system and 'should' stiffen up the brake feel at least.  Whether or not it improves the actual function or not, I don't know.  I have another couple tricks up my sleeve for that so we'll see if I can experiment with those too.

This first operation requires rotating the drum housing/pivot arm around the axle.  To do this, the locating boss on the fork leg needs to be modified (in this case I cut it right off in order to be able to measure and prototype a solution) and a new bracket/boss will take its place - one that fits in the slot and can be adjusted in angle increments about the center of the axle.  Prototypes coming soon...
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: jpmobius on Aug 30, 2018, 12:45:07
What's the plan for the cable as the suspension moves?  The brake cable could telescope through guides and bend where it needs to go to the lever, but the speedo cable is a pretty straight shot with no place to curve away when the suspension compresses.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Aug 31, 2018, 03:37:22
What's the plan for the cable as the suspension moves?  The brake cable could telescope through guides and bend where it needs to go to the lever, but the speedo cable is a pretty straight shot with no place to curve away when the suspension compresses.

Yeah exactly, the cable will run through an eyelet - like on early motocross bikes.  The speedo cable is however more tricky.  If I was keeping it, I would need to create an extra loop somewhere I guess?  Or a universal joint?  Ahahah

But for this bike it won't matter, I'll be plugging that hole with one of the tach plugs I designed and will use an electronic speedo with a pick up instead - hoping this will be more accurate for speed. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Aug 31, 2018, 07:56:57
Last night I tried experimenting with the idea of getting the front brake cable to run parallel with the fork leg - so that the lever is at right angles.  This removes cable length and bends in the system and 'should' stiffen up the brake feel at least.  Whether or not it improves the actual function or not, I don't know. 

Regarding your question: This improves the front brake to no end and not only the lever feel, but the actual and measurable performance. But you have to set up the lever so it only hits 90degrees at full pull of the cable. Going over this point will decrease the length of the lever and thus make the brake feel worse again.

(It's a common thing on XT500s to tune the front brake like that and same goes for the rear drums of both  my 4-valve xt and my TR1.)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 03, 2018, 03:48:59
Great thats good to know nanno!  The bracket will be a bit adjustable to I am hoping to be able to play with that angle. I always think it's much cooler to improve on something already there with a bit of ingenuity, rather than just swap it out entirely.  I think that's the kiwi in me.

While on this topic, I was thinking of designing a billet lever arm - a bit like the ones for the SR and XT500.  But when holding the stock pressed metal one in my hand and looking at it, I just can't imagine a new arm would or could be any stiffer - the stock one has all it's stiffness in the right direction.  Plus I don't think there would be any weight savings to speak of.  Thoughts?

Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Sep 03, 2018, 15:03:39
These look nice. That's about it. Look at the rear (ally) brake lever of a 1984 to 1986 XT600, basically the same bit except the fancy nut.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 07, 2018, 05:57:24
I dismantled the forks this week to get a closer look at the damping rod, spring and circlip groove. 

I tested the circlips I ordered and they work a treat.  This is definitely what I will be using in the future and will specify with any eventual kit I might develop.  Now it would be a one hand job to remove the clip (with circlip pliers of course), instead of 3 hands a lot of swear words.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Sep 07, 2018, 12:10:12
I think circlips is a great idea! Don't know why they were never used in the first place as they can't cost that much more and would greatly improve assembly/repair times.
Also looking forward to any quantitative measurements on the front brake mods as I cannot imagine that ventilation holes and lever repositioning will beat replacement with a disk brake (and its subsequent improvements on both swept square inches and cooling).
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Sep 07, 2018, 13:56:41
I use circlips on all the dampers I build, no threads at all. Makes rebuild like a 10 minute process. The downside I think is that they are a little more finicky and they are more tempting for people to mess with. They also have less shear than a threaded item, but in many cases they are good enough. Machining the grooves is generally much easier.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: goldy on Sep 08, 2018, 09:01:24
The way the original clip works, they are basically locked in place by the relief cut in top slug and cannot be easily dislodged. The snap ring you are using isn't locked in place at all. The whole mass of the front end is being held on that snap ring. Having said that, I am currently working on a set of GT 750 forks with exactly the same modification...they have been in service for a very long time with no adverse effects and like you mentioned, they are a heck of a lot easier to get apart!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 10, 2018, 11:36:01
I think circlips is a great idea! Don't know why they were never used in the first place as they can't cost that much more and would greatly improve assembly/repair times.
Also looking forward to any quantitative measurements on the front brake mods as I cannot imagine that ventilation holes and lever repositioning will beat replacement with a disk brake (and its subsequent improvements on both swept square inches and cooling).

Yeah, will be good to see if any noticeable difference.  Might be hard to quantify though - the human bias to change (seat of the pants) is pretty strong.  I guess some brake test scenario could be laid out and back to back tests with original set up and new set up could be done - if I get to it.

I use circlips on all the dampers I build, no threads at all. Makes rebuild like a 10 minute process. The downside I think is that they are a little more finicky and they are more tempting for people to mess with. They also have less shear than a threaded item, but in many cases they are good enough. Machining the grooves is generally much easier.

Great to hear!  Yes, I was/am concerned about sheet as well...  I guess I could have a buddy from work to an FEA on the circlip and see what forces it takes to deform it based on the way it is held in the groove and the material specs.

The way the original clip works, they are basically locked in place by the relief cut in top slug and cannot be easily dislodged. The snap ring you are using isn't locked in place at all. The whole mass of the front end is being held on that snap ring. Having said that, I am currently working on a set of GT 750 forks with exactly the same modification...they have been in service for a very long time with no adverse effects and like you mentioned, they are a heck of a lot easier to get apart!

Very good to know, yes, am quite concerned about this.  I wonder if I could get around the issue of 'locking it in place' by designing some recess groove in the new fork caps I will design - so that the circlips can only be removed in one orientation, otherwise they are trapped in the stanchions undercut and cap groove.  But the best is that you have had the same solution in operation for an extended period!  This gives me faith.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 13, 2018, 14:13:38
A completely random item...  The oil filter drain screw.  I wanted to offer these to my customers and when I drew it up I decided to get a quote in Ti as well as steel.  The price difference was around 20% (most of the cost is programming and machine time, then material is marginal). The part is really nicely made and great quality!  Astonishing that the weight is nearly half the stock item.  This is negligent in the scheme of things, but I figure after this wee experiment I will try to put together a Ti engine bolt kit.  One of Cosworths suggestions from the last build. I figure if I could offer them in black, silver and gold that would be a cool detail item that could appeal to many and give some weight savings to boot.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 16, 2018, 14:43:15
Here is some of the development of the re-positioned brake lever/perch/arm.  At first I thought it would be logical to do like I have seen on other bikes with a control arm located on one of the guard bosses (which then goes down to a boss to hold the brake rotor in place) - as seen in the first couple of pictures. 

But then I thought again and decided there must be a way to design a special bracket to use the existing boss in some way - so instead of cutting it off entirely, I modified it so the brake rotor/drum brake housing could rotate freely without interfering with it.  Then when sketching up the idea I saw that it could be adjustable as well - to be able to achieve the correct brake lever arm angle with any given/decided tension/brake trim.  The pictures explain most of the idea.  This way, the parts can be smaller, weigh less and be less of an eyesore.  Plus, it will allow me to shave the fork legs like I want to do (like the other SR I built) and just have the fork brace there holding the guard instead.

The bracket could also be further developed to include a boss that extends rearward and holds the brake wire itself - in cases where the stock brake cable perch is damaged.  But this will not be examined this time round.

The last prototype works relatively well/as intended.  However it does not sit on the fork leg boss securely enough.  I am designing a further prototype now where the boss gets bolted to the brake housing through the backside - removing as much play in the system as possible.  Hopefully I'll be able to print and test this during the week.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Sep 17, 2018, 01:55:34
The angles are looking good!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: doc_rot on Sep 18, 2018, 11:57:12
what if you made the opening around the locating boss on the fork slotted so you could add a pinch bolt there to remove slop even further.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: jpmobius on Sep 18, 2018, 14:05:28
what if you made the opening around the locating boss on the fork slotted so you could add a pinch bolt there to remove slop even further.
I think this is a good idea.  In all things brake related, it is wise to consider what will happen if a critical component fails.  This is such a part where failure would be considered catastrophic.  I think there is no issue that the component will be strong enough, but keeping it in place is another matter.  One of the issues I see is the draft in both the boss and the recess in the backing plate.  Regarding the boss on the fork leg, I think adding a thick section to the plate that would fit between it and the backing plate would prevent the plate from slipping off the boss.  Not sure how that would affect being able to assemble the parts.  Machining the boss so that the working faces are parallel and perpendicular to the load would remove the propensity of the existing draft be a ramp and allow it to slip off of the boss, as well as greatly reduce the wear and make for a much improved capacity for being clamped by a pinch bolt.  The other side where it fits into the notch in the backing plate has the same issue, but that would seem to be an easy fix by simply using longer bolts that can thread into the backing plate.  I don't see any value in the adjusting slots - just drill holes in the right spot - the slots are just another thing to come loose and cause trouble.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 28, 2018, 12:07:31
Thanks for all the input guys!  It means a lot.  I think what I will do now is a combination of your ideas.  I will remove the slots - jp is right, if it is in the correct position from the beginning, it shouldn't need adjustment.  Then if I do that, why not combine the boss into the bracket (to make that one piece) - to eliminate any movement there too (if this still allows the wheel to be mounted).  But I will also make it so that the drum plate is fastened to the bracket completely - both at this boss, but also at the bracket.  This will eliminate the slop we are concerned about.  I think this is the best compromise to fasten it to the fork boss - because yes, as jp points out, that boss has draft on it and would be impossible to add a pinch bolt to - without machining it flat ofc.  I'll draw up a new prototype over the weekend and see if it'll work!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Sep 28, 2018, 12:11:28
I have a theoretical question while I'm at it...  Would there be any difference if the brake arm was pointing forward or rearward?  Still so it is perpendicular to the fork leg, just that the wire is up front or behind the fork.  I can't see how it would be any different, but may allow for even easier cable routing from the brake lever on the handle bar...
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: jpmobius on Sep 28, 2018, 13:50:45
If the cam that pushes the shoes apart is symmetric, it does not matter which way it turns so you could flip the arm over and have the cam rotate backward.  However, you would have to make a new mount for the cable housing, and have an all new design for a plate to keep the brake plate from turning. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Sep 28, 2018, 15:59:08
Isn't that a speedo drive in the brake hub?  Flipping it won't for that, as much as it wouldn't work for the stay.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Oct 01, 2018, 03:34:41
If the cam that pushes the shoes apart is symmetric, it does not matter which way it turns so you could flip the arm over and have the cam rotate backward.  However, you would have to make a new mount for the cable housing, and have an all new design for a plate to keep the brake plate from turning.

Just what I thought.  Thanks.

Isn't that a speedo drive in the brake hub?  Flipping it won't for that, as much as it wouldn't work for the stay.

In this case, the speedo drive will not be used anyway, so it's position is not considered.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Oct 01, 2018, 03:37:59
This is my latest idea.  Why not try to replicate the what the stock brake plate does, but just reposition it?  So now the idea is to bolt the bracket to the plate, then have it slide up onto the fork boss - like the stock one - as you install the wheel.  Then the last step is to install a bolt, not necessarily a pinch bolt, rather an encapsulating bolt that just holds it in position and increases the strength of the bracket.  I'll give it a shot with a prototype anyway.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Pod70 on Oct 10, 2018, 12:42:31
Please take this as a constructive observation rather than criticism but I think you may going in the wrong direction with the brake cable mod. As I understand it the 2 key points to an effective cable operated brake are:

1. The angle between the cable and the cam lever should be kept as close to 90 degrees at the minimum and maximum points of the pull (brake off & on) this is governed by the position of the cable retainer on the drum and the length of the cam lever. Rotating the drum around as you have done is not going to alter this but correct setting up of the cable, lever etc. will

2. Sharp bends in the cable need to be avoided to prevent the inner cable binding against the outer cable and you must check this at max & min suspension travel as well as from lock to lock. Having the brake lever on the right and the brake plate on the left ensures that the cable doesn't bind or twist in the cable adjuster at the lever thanks to the straight run of the cable along the handlebars and then a gentle curve down the left fork leg followed by a gentle curve towards the cable attachment point on the drum. The first curve allows for the movement of the handlebars and the second allows for the compression of the forks.  Removing the 2nd curve could cause binding of the cable when the suspension is compressed especially on a road bike with less suspension travel than the off-road forks shown earlier in the thread.

Adding the bracket will only increase the unsprung weight (not a good thing) and potentially introduce more flex into the system (definitely a bad thing)

I hope my points are helpful by coming from a (literally) different direction and keep up the good work
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Oct 10, 2018, 15:11:26
WRT fork springs - were you able to locate any CB360/400F or RD250/350LC fork springs for experimentation? I've seen some new CB360/400F fork springs on ebay in varying rates so would be very interested in fitment to the SR250 forks.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Oct 16, 2018, 03:43:56
Please take this as a constructive observation rather than criticism but I think you may going in the wrong direction with the brake cable mod. As I understand it the 2 key points to an effective cable operated brake are:

1. The angle between the cable and the cam lever should be kept as close to 90 degrees at the minimum and maximum points of the pull (brake off & on) this is governed by the position of the cable retainer on the drum and the length of the cam lever. Rotating the drum around as you have done is not going to alter this but correct setting up of the cable, lever etc. will

2. Sharp bends in the cable need to be avoided to prevent the inner cable binding against the outer cable and you must check this at max & min suspension travel as well as from lock to lock. Having the brake lever on the right and the brake plate on the left ensures that the cable doesn't bind or twist in the cable adjuster at the lever thanks to the straight run of the cable along the handlebars and then a gentle curve down the left fork leg followed by a gentle curve towards the cable attachment point on the drum. The first curve allows for the movement of the handlebars and the second allows for the compression of the forks.  Removing the 2nd curve could cause binding of the cable when the suspension is compressed especially on a road bike with less suspension travel than the off-road forks shown earlier in the thread.

Adding the bracket will only increase the unsprung weight (not a good thing) and potentially introduce more flex into the system (definitely a bad thing)

I hope my points are helpful by coming from a (literally) different direction and keep up the good work

Thanks for the input Pod!  This mod is inspired by these guys here: https://www.klemmvintage.com/bighorntech.htm  They are serious vintage racers and don't usually do stuff just because.  The mod makes sense to me and it seems like a simple way to improve brake 'feel'.  How much it actually improves mechanically is up for debate  ;)  But eliminating big sloppy loops in the wire is the number one goal (pretty much what you're getting at in point 2 of your reply).  With the set up using this bracket, there will essentially be one soft 90 degree bend in the wire (at the handle bar just after the lever).  Otherwise it will be running straight up and down with the fork leg.  I also don't understand why all offroad bikes from this era with front drum brakes have this set up, road bikes didn't?  Something to do with the speedo cable drive outlet?  Offroad bikes didn't have this but road bikes do/did?

Point taken about the unsprung weight.  I agree.  But hopefully the 'drillium'  ;D will have helped here plus the fact I have removed half of the boss on the fork leg - so maybe I am back to plus minus 0.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Oct 16, 2018, 03:47:01
WRT fork springs - were you able to locate any CB360/400F or RD250/350LC fork springs for experimentation? I've seen some new CB360/400F fork springs on ebay in varying rates so would be very interested in fitment to the SR250 forks.

I haven't come this far sorry Zap.  What I will do, both for my own sanity and for others wanting to improve the SR's front end, is create sort of a cost vs benefit spreadsheet - where I included things like new springs, spacers, adjustable fork caps, valve emulators etc and see where is all ends up.  Maybe none of it is worth it, maybe all of it is, but probably there is a nice balance.  Also see this next post about what I have been drawing up for fun...

I have also got stuck with this damn brake perch, the angles and fitment have been baffling me.  I am (embarrassingly) on like the 10th prototype  :o  I'll put up a post when it is all sorted.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Oct 16, 2018, 04:07:28
I will hopefully picking up my wheels this week - with the tyres mounted.  This will give me a rolling chassis where I can start working out my ride height, suspension travel, rake and trail.  Very exciting.

This got me inspired to finally start on something for the forks.  At this stage, I am planning on testing two routes, a budget route and an expensive route and I will then test the performance difference (if not too subjective and hopefully measurable???). 

Cheap route - little like the Minton mods for the XS650 forks:

1) Investigate the use of 33mm fork seals (instead of the SR's 32mm) to reduce stiction - read about the Minton mods before calling me an idiot
2) Drill up the damper rod holes a size (just a little) and countersink the holes (better oil flow in and out of the orifices)
3) Cut out the soft part of the stock SR spring (remembering this is a dual rate spring, not a progressive spring) and replace that length with a spacer
4) Install custom fork caps with a circlip that are easy to remove
5) Play with preload by installing different length spacers under this cap - the ones that sit on top of the stock cut spring
6) Play with fork oil viscosity and level (perhaps via a convenient hole in the fork cap that oil can be added and removed from, them plugged - without removing the entire cap).

Expensive route:

1) Drill out the damping rods so they are in essence, useless
2) Install valve emulators (correct size exists, just need to order)
3) Investigate either custom progressive springs for the SR or as Zap mentions, CB360/400 or RD250/350 springs
4) Install custom designed adjustable fork caps (with 20mm preload adjustment)
5) Still play with fork oil viscosity and level

This will be fun to mess around with and likely improve the front end a lot, even by doing little - because it is so useless stock.

There is one more possibility on the table that I haven't figured out yet - that is designing the caps to have an air valve in them to be able to convert the forks to air dampened assist (same as my mountain bike).  I have little knowledge of this so am less inclined to test.  But it wouldn't be too difficult to implement. 

Attached are a couple ideas I am working on for the adjustable cap version.  Whether or not this works out from a cost benefit point of view, I don't know.  But for me it is a lot of fun to draw up concepts.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Pete12 on Oct 16, 2018, 13:04:18
Not sure whether you can do this on your forks or not but on my RD flat tracker I used Kawasaki forks that had a circlip holding the caps in place, so I just machined an internal thread in them and used conventional fork caps.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: XS750AU on Oct 16, 2018, 23:06:09
Quote
This got me inspired to finally start on something for the forks.  At this stage, I am planning on testing two routes, a budget route and an expensive route and I will then test the performance difference (if not too subjective and hopefully measurable???). 

So how are you going to measure success?
I have bought a few bikes, the Husaberg in particular, where the PO had wound up the preload, compression dampening and rebound to a point the bike was unsafe. It would spit you off at the first bump, no wonder he sold it so cheap! Backed it all off so the wheels could actually react and now it is beautiful bike to ride! It is much softer, but it does not bottom out and the wheels stay engaged with the track (except when airborne)  ;D.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 06, 2018, 03:37:13
Not sure whether you can do this on your forks or not but on my RD flat tracker I used Kawasaki forks that had a circlip holding the caps in place, so I just machined an internal thread in them and used conventional fork caps.

Thats a great idea!  Unfortunately I don't have the equipment for that :(
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 06, 2018, 03:38:43
So how are you going to measure success?
I have bought a few bikes, the Husaberg in particular, where the PO had wound up the preload, compression dampening and rebound to a point the bike was unsafe. It would spit you off at the first bump, no wonder he sold it so cheap! Backed it all off so the wheels could actually react and now it is beautiful bike to ride! It is much softer, but it does not bottom out and the wheels stay engaged with the track (except when airborne)  ;D.

I would say that not so many people would completely understand what they are adjusting when they adjust things on their suspension.  Most would just expect harder/softer rather than different damping settings.  Glad you got a good bike out of it though!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 06, 2018, 04:05:35
Here's the first (well actually third after a couple failed attempts) prototype for the stock fork cap replacement.  This makes it a one man job to rebuild the forks and a much easier process - push the cap down with one hand with a tool guided in a pocket/recess in the cap (for this purpose - so the tool doesn't slip out), then once it is in the correct position, the other hand can clamp the circlip and let it sit into it's groove.

Then once it is in position, the cap lifts up and actually holds the circlip in its relaxed state - by the shape of the top machined detail.  So to release the circlip again, the cap needs to be pushed down a little to pass this detail - an extra safety/security feature (think I got this idea from one of you guys in an earlier response?).

I will experiment with the length of it now and see what I can do with interchangeable spacers. 

Oh yeah, the cap will also have a machined top, held in place with an oring - to keep the whole assembly water tight.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: 2Planks on Nov 06, 2018, 10:34:32
YES! I just battled mine. Had to be the first time the forks have been apart. I slipped off the plug when putting it back together. Glad the piece didn't hit me. You're doing gods work Jadus
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: hooligan998 on Nov 07, 2018, 01:01:22
What is the material you're using and is it machined or 3D printed.  Pretty cool work.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 07, 2018, 03:47:23
Thanks guys.

The plastic is PLA and the method is FDM from a Printrbot printer.  It is not the best printer but it works very well for my purposes  :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 08, 2018, 03:32:56
I finally got my custom copper head gaskets for this project as well.  0.5mm thick (and with a larger opening to fit the 77mm piston) giving 10.2:1 compression ratio.  I also took the chance to order another version for a boosted stock engine (with standard bore) at 1.5mm thick, giving 8.3:1 compression - good for 6-8psi of boost.

Yes, on the side I am working on a supercharged SR250 project...  It is going very slowly though and taking a back seat to this project.  Although I am finding there is a lot of nice cross over research and design work.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: advCo on Nov 08, 2018, 10:15:39
Despite the fact that I haven't found an SR250 yet, I enjoy watching your prototyping and product design processes. Keep up the good work!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: 2Planks on Nov 08, 2018, 12:28:13
Thanks guys.

The plastic is PLA and the method is FDM from a Printrbot printer.  It is not the best printer but it works very well for my purposes  :)

Question im going to be re gearing my exciter. Have you messed with different set ups?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Habanero52 on Nov 08, 2018, 19:12:16
I finally got my custom copper head gaskets for this project as well.  0.5mm thick (and with a larger opening to fit the 77mm piston) giving 10.2:1 compression ratio.  I also took the chance to order another version for a boosted stock engine (with standard bore) at 1.5mm thick, giving 8.3:1 compression - good for 6-8psi of boost.

Yes, on the side I am working on a supercharged SR250 project...  It is going very slowly though and taking a back seat to this project.  Although I am finding there is a lot of nice cross over research and design work.
Who made them for you?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 09, 2018, 03:21:17
Despite the fact that I haven't found an SR250 yet, I enjoy watching your prototyping and product design processes. Keep up the good work!

Thanks man, love your CB build!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 09, 2018, 03:26:53
Question im going to be re gearing my exciter. Have you messed with different set ups?

I have done in the past, I think I ended up with 17-40.  But I will look more into it when the time comes.  I know there are online calculators that help you work out rpm at certain speeds with different gearing ratios.  I will be looking for max power output at around 170kph so I have the tip of the torque curve around the 100mph mark so this gearing will be very different to stock bikes.  I will also be hoping to have power to 10,000rpm as well.

While on this topic, I have studied the parts diagrams for both the SR250 and the XS250 gearbox's - the latter because it is a 6 speed!  From the diagrams I could tell they weren't compatible but I found a good deal on a whole set up on ebay so I bought it anyway, in the hopes of learning something or maybe even swapping some ratios.  I learned something for sure, but this idea is a dead end - just look at the differences in the photo - SR250 gearbox at top (most of it), XS250 gearbox at bottom (all of it).  Very different beasts!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 09, 2018, 03:29:34
Who made them for you?

John from http://gasketstogo.com/  :D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Nov 09, 2018, 17:52:49
As a turbo-bike-builder... which s/c are you thinking about? AMR300 or have you found something even smaller?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 10, 2018, 10:53:36
As a turbo-bike-builder... which s/c are you thinking about? AMR300 or have you found something even smaller?

Nope, you got it!  I managed to source a refurbished AMR300 from alibaba.  It seems in pretty good shape.  I will draw up custom billet intake and outlet ports for it to bolt up to the SR carb and then the engine on the other side (with a plenum-ish thing).
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Nov 10, 2018, 15:05:45
If you go draw through, you want as little plenum between engine and supercharger as possible... AMR300s are nice. In your case run it at roughly 1:1 and you should see about 3psi + a bit for the inefficiencies of the engine, so just about enough to make you lust for more and then go completely bananas on the boost level.  8)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 14, 2018, 16:00:22
After being at the motorcycle workshop FOREVER (seems like vintage bikes here get very low prio) the tyres have finally been mounted on the wheels - and they look great.  These Avons can be mounted front or back and have a mounting/direction arrow to indicate which direction for which wheel (front or back).  Somehow, despite me writing in large text in permanent marker on the rim, the workshop managed to fudge this as well.  They were embarrassed and fixed it onsite for me while I waited.  So they should.

Anyway, next stop, rolling chassis! 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Tim on Nov 14, 2018, 20:11:33
Awesome tires - nothing like a set of fresh wheels all ready and waiting.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: hooligan998 on Nov 15, 2018, 00:47:12
Ssssseeeexxxaaayyyyy wheels!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 18, 2018, 09:03:51
Before I put the wheels back on I really want to sort out the suspension.  The rear will be relatively straight forward after the front is sorted.

For the front I have been investigating what can be done with the stock springs and cutting them.  I managed to work out what the stock spring rate is with the dual windings, it is a really low 3.3N/mm, which according to some literature, is suitable for riders weighing less than 50kg!  Haha.  Now I don't know if I am exactly right with all this stuff but it makes pretty good sense to me - see that attached equation plus the weight/spring rate charts from various manufacturers.  Many replacement springs for classic bikes are however much higher ratings - up towards 7-10N/mm for riders ranging from 75-105kg.  I'll do some of my own experimenting.  The second rate on the spring is a lot more in the ball park at 4.5N/mm. 

I started out investigating cutting the spring in three locations, one to separate the dual rate, then another two cuts to shorten each spring based on a percentage increase in spring rate - see attached how I thought a spacer could be made to connect the two and keep their compression separate, plus a chart of some calculations I made.  This way, the dual rate could be retained.

Once I did the calculations and did a test cut of the spring, I realised this is not a good idea.  The tightly wound part of the spring becomes coil bound quite quickly (did a test compression) and becomes useless (this is the purpose/intended behavior), plus cutting in a few places is a pain.  I figured after reading a lot, especially racetechs literature, that straight rate springs with correct rate, preload and damping are much easier to control, adjust and ultimately will behave as intended = predictability and hopefully a well performing fork.

One good thing that came of the exercise though is the spacer I designed to be able to receive the cut end of the spring and provide a flat landing at the other side of it.  The spacer matches the angle of the spring in its relaxed state and collects the end of the cut spring perpendicular to its winding.  This gives the whole first coil and the end support.  I will use this moving forward.

Now I will start experimenting with cutting out the tight windings completely and work out some suitable spring rates by cutting out a certain amount of coils (and calculate for a suitable amount of initial preload as well).
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 18, 2018, 09:08:55
And a prototype of this spacer.  Works well.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Nov 18, 2018, 19:49:15
Very interesting work! I did read that the CB400F/360 fork springs may need to be cut (that's if they do fit in the SR250 tubes) so your cut spring adapter may come in real handy. Much easier than trying to grind off the cut end.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 21, 2018, 04:11:21
Very interesting work! I did read that the CB400F/360 fork springs may need to be cut (that's if they do fit in the SR250 tubes) so your cut spring adapter may come in real handy. Much easier than trying to grind off the cut end.

Yes, it could work with different springs, so long as the dimensions were somewhat similar.

I ask the question though, why change springs if the stock one is up to the job when it is cut and stiffer?  As long as it is within its working range when fully compressed...  I looked into springs from the RD250/350s and the CB360/400s and yes, there are many available in different rates, but they range in price from 110usd for straight rate to 180usd for progressives.  Perhaps the SR spring can provide the same performance if the right math/calculations are done for rider weight, length - resulting in rate, and finally preload? 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 21, 2018, 04:13:38
Anyway, here are the results of testing the stock SR250 fork spring so I know more about how it looks and behaves in use.  Interesting!  Now I can start experimenting.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Nov 21, 2018, 19:52:10
Yes, it could work with different springs, so long as the dimensions were somewhat similar.

I ask the question though, why change springs if the stock one is up to the job when it is cut and stiffer?  As long as it is within its working range when fully compressed...  I looked into springs from the RD250/350s and the CB360/400s and yes, there are many available in different rates, but they range in price from 110usd for straight rate to 180usd for progressives.  Perhaps the SR spring can provide the same performance if the right math/calculations are done for rider weight, length - resulting in rate, and finally preload?

Because the original springs (both front and rear) were specified as such to support a rider/passenger of a specific weight. If your projected load is not fairly aligned with that design parameter, then it will not matter much how much preload you introduce (until you fully compress the spring). Being somewhat self-serving here as I weigh somewhere in the neighborhood of 260-270 lbs when suited up (still way under the stated max load), as are many USA riders judging from the many discussion threads on suspension mods of all sorts of bikes. This is the reason of my interest in different springs with stiffer rates for the forks. Keep up the good work!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 22, 2018, 04:21:09
Because the original springs (both front and rear) were specified as such to support a rider/passenger of a specific weight. If your projected load is not fairly aligned with that design parameter, then it will not matter much how much preload you introduce (until you fully compress the spring). Being somewhat self-serving here as I weigh somewhere in the neighborhood of 260-270 lbs when suited up (still way under the stated max load), as are many USA riders judging from the many discussion threads on suspension mods of all sorts of bikes. This is the reason of my interest in different springs with stiffer rates for the forks. Keep up the good work!

Great input zap, thanks.  Very good points.  I might, for the sake of research, buy a cheap second hand set of springs from these mentioned models of bikes just to see if they fit and could work.

One important point about the stock SR springs though; if they are cut, the rate increases with every coil removed.  By the time you remove 5 of the working coils of the main spring, the rate is already up past 5N/mm - which is more suitable for a 90kg rider.  I will need to test this of course with the threaded rod jig to see how much stress is put on the cut spring when it is compressed the 140mm (plus maybe 10-20% preload) of travel.  Perhaps this much movement with a shorter spring will put it outside of its working range and begin to deform it over time.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Nov 22, 2018, 22:16:26
Great input zap, thanks.  Very good points.  I might, for the sake of research, buy a cheap second hand set of springs from these mentioned models of bikes just to see if they fit and could work.

One important point about the stock SR springs though; if they are cut, the rate increases with every coil removed.  By the time you remove 5 of the working coils of the main spring, the rate is already up past 5N/mm - which is more suitable for a 90kg rider.  I will need to test this of course with the threaded rod jig to see how much stress is put on the cut spring when it is compressed the 140mm (plus maybe 10-20% preload) of travel.  Perhaps this much movement with a shorter spring will put it outside of its working range and begin to deform it over time.
You are correct of course - it is the reason that adding preload helps to hold up more load weight. But at the cost of suspension travel. I would be looking for the same travel but able to hold a (I suspect much) higher load weight without additional preload.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 26, 2018, 05:03:12
Have been spending a lot of time in CAD and prototyping trying to get the adjustable preload caps to fit and work within these unique constraints of this fork.  Remember, all other adjustable caps are screwed in place!  After a few attempts and failures, I think I have something that is close enough it is worth doing some engineering drawings and getting some metal prototypes machined up.

The idea is that the caps are installed easily as in my previous prototype, then locked in place with the circlip.  The adjustment rod has an M10 thread and provides 20mm of adjustment.  It is also completely removable so that fork oil can be added or removed with a 6mm tube (through the hole in the adjustment plate/spacer), allowing fork oil height adjustment without needing to remove the entire fork cap.  I have found suitable sized orings for each component as well and adjusted the parts to suit.  I still need to order them though - hence the prototypes missing them.

Thoughts?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: pidjones on Nov 26, 2018, 08:00:57
Make sure that when you get real ones, the circlip is installed with the sharp edge UP (away from the spring).
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Nov 26, 2018, 09:45:01
Make sure that when you get real ones, the circlip is installed with the sharp edge UP (away from the spring).

Yes!  Great point.  Will provide a healthier land/contact patch for it against the groove in the stanchion.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Nov 27, 2018, 06:38:35
I really like what you did there.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 01, 2018, 06:44:06
YSS fork emulators in the correct size (almost!) arrived this week!  Can't wait to install and test them.  Like any curious engineer, I took them apart to see how they are built up.  Pretty nice stuff.  Good quality and impressive fitment/tolerances.

Only thing is, they don't quite fit into the SR's damper rods like they are supposed too.  I'll turn that small piece of aluminium down on them so they fit nice and snug there.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 09, 2018, 12:33:12
I did end up ordering both a set of springs for the RD250 and CB400 to see if they fit.  They were second hand and cheap and they should arrive this week.

I also bolted up the wheels to get this project's first rolling chassis!  Woohoo!  Haha, no, now I will draw the basic geometry into CAD and work out what specifications I want and how I can achieve that - fork height, rear shock length, ride height, rake/trail and different to the other bikes I have built...  ground clearance!  This will be worked out with rearset bracket position as well.  Something that has frustrated me with previous SR250 builds is the lack of ground clearance when cornering hard.  I don't think these bikes were designed to corner hard but they should be able to with the right upgrades and some better foot clearance - the pegs are always the problem.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: pidjones on Dec 09, 2018, 17:05:48
When I was 165 lbs, the RD250 was way undersprung. The RD400 was just right.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: CrabsAndCylinders on Dec 09, 2018, 17:35:26
When I was 165lbs the RD250 wasn't even on the drawing board :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Dec 09, 2018, 18:17:14
When I was 165lbs I was around 13 years-old. Of course when I was in 6th grade I was the tallest person there - including the teachers and principals.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 10, 2018, 03:11:25
I weigh 165 now, but remember a couple years ago weighing, as phife dawg from A Tribe Called Quest says; 'A buck fifity'! So the RD400 springs should be good!  I'll be able to work out their rate from the dimensions and number of coils and apply that to the SR spring (hopefully).
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Dec 27, 2018, 12:34:55
Seasons greetings all!

I took the couple days off this week between Xmas and NYs while my GF is at work so I can be in the workshop  ;D

Just before Xmas I received the machined brake perch repositioning bracket.  Which I have been pretty quiet about since the last time I mentioned it - that is because it took an embarrassing amount of prototypes to get it right!  The angle and position on the fork was just doing my head in.  Anyway, it came up mint and works a treat.  Now I just need to make a small eyelet for the brake cable to move through and specify a custom cable for Venhill to make.

You can see I took some advice from a few of you with the way that it is mounted.  The only difference really is that the bolt does not act like a pinch bolt (because of the 3 degrees draft on the leg boss), rather it is just done up tight enough with a lock nut so that it holds itself in position and stable, and takes the braking loads together with the bottom piece of the opening in the bracket.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Dec 27, 2018, 14:08:00
That came out really well.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: pitobread on Dec 28, 2018, 02:01:10
That's a beauty.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Dec 28, 2018, 16:03:46
Nice setup.

The brake lever should be set up one notch lower, or you pull it over 90 degrees.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: pidjones on Dec 28, 2018, 21:13:46
Nice setup.

The brake lever should be set up one notch lower, or you pull it over 90 degrees.
Plus, you'll get a bit more adjustment room on your cable.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 07, 2019, 07:03:39
Thanks all!

Nice setup.

The brake lever should be set up one notch lower, or you pull it over 90 degrees.

Great point!  Will do when setting up in the final assembly.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 07, 2019, 07:07:46
Somewhat but not entirely related...  Have spent a lot of time the last couple of weeks filming my wheel building process and editing it together as an instructional video.  Now that wee project is complete work will continue with the this build!

To build wheels I came up with this taping method.  Perhaps others do this too?  Anyway, I find it makes a headache of a process into a pleasantly therapeutic one. 

https://www.youtube.com/watch?v=Mj_JUgpImB4&t=337s

I also wrote a blog post about spoked wheels.  They are rad!  https://www.jadusmotorcycleparts.com/single-post/2018/12/30/Spoked-Motorcycle-Wheels---The-Best-Motorcycle-Wheels
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 10, 2019, 13:53:54
Both sets of fork springs finally arrived this week and both fit! 

Now I can work out the spring rates of both sets and draw up some spacers to make them work.

I am however having second thoughts.  After seeing these, I am actually thinking it might be better to use cut stock SR250 springs, calculate the necessary length for the necessary/desired rate, then make some spacers for that and use the spring end adapter I designed.  Then I can get testing the performance of these and if it's good, it could be something to offer customers - a much cheaper solution to buying springs from other bikes and saves shipping hassle as well. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: pidjones on Jan 10, 2019, 14:29:36
Just as long as you don't coil-bind.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jan 11, 2019, 07:40:10
Just as long as you don't coil-bind.

Good call.  I'll be able to check that with my threaded rod set up and a few measurements. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 11, 2019, 13:06:29
Not so much to post for a while but things are ticking along.  I developed a simpler fork preload and cap kit to see if I could bring down the cost of production for customers - more on that later.  Plus I checked a lot more things with cutting the stock springs - worked out lengths, rates, preloads and suggestions for rider weights.  I also checked how the spring would be at full compression at it most extreme cut length - see attached.  The adapter I designed works a treat to spread the load of a cut spring end.

I ordered a magnetic angle finder as well that works off of level - so you can place it on the fork stanchion and work out rake and therefor trail as well.  I need to do this because the current set up I have with an experimental rear shock length of 350mm ends up with 23 degrees rake and only 85mm trail.  I want 100mm of trail minimum for this slightly higher speed SR and certainly more rake than that.  So I will therefor work with rear shock length and front fork lowering to achieve this.  Rake will land between 26 and 28 degrees.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 17, 2019, 09:13:49
So the angle finder came and is awesome.  What a great way to measure these things with pretty good accuracy.  Anyway, I worked for some time with rear shock height and lowering the front forks until I got something acceptable.  One problem is that I am still a little driven by the look and proportions of the build - so I wanted to achieve this flat line of the seat and tank still.  This meant a slight compromise for these figures.  But I ended up with a rake angle of 25.5 degrees and trail of 95mm.  Which is a little border line but still within the acceptable realms of sport bike specs.  When I get the bike running I will be careful when coming up to speed at first and if it feels necessary I can install a steering damper as well.

The final rear shock height is 340mm and the front forks are lowered 40mm.  I double checked these physical measurements with a quick CAD sketch and they are almost spot on - meaning they are reliable figures/measurements. 

Now I just need to find a rear shock that is in that length and is soft enough for a 100-110kg bike...  There are plenty of rear shock options for that length with the correct 14mm diameter eyelets, but they are all for much heavier bikes.  This would mean a very stiff spring and almost non-functioning rear suspension.  I have written to a few companies inquiring about custom set up YSS shocks.  Anyone got any other suggestions?  I would consider Hagons if their shocks didn't look so damn vintage!  And I haven't heard very good things about RFY shocks (shame because they look cool).
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 17, 2019, 12:13:15
And here's how those dims/set up looks.  You can see that the rear frame rails are parallel to the ground - one of the visual goals I couldn't let go of.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: pidjones on Feb 18, 2019, 07:58:16
I wouldn't worry as much about coming up to speed as backing off from speed. The front dives, rear lifts, and both decrease trail.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 18, 2019, 10:17:22
I wouldn't worry as much about coming up to speed as backing off from speed. The front dives, rear lifts, and both decrease trail.

Very true.  Unfortunately I can't see another way to increase trail without compromise.  There is one option left and that is to design some custom triple tree clamps with less offset to increase trail.  Because the rake/caster is actually pretty good.  But then if I am designing custom triples, I may as well install a modern fork.  And I really don't want to do that!  Maybe I should look into an anti-dive system  ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Feb 27, 2019, 16:03:14
And now for something completely different...  I was/am not planning on spending much time on styling/finishes on this build as I did with the last build.  But that doesn't mean it won't look cool, just a little more function over looks.

Anyway, I was going to go for a completely raw, materialistic look - all aluminium parts bare aluminium, all metal parts rattle canned black and then I was going to strip the tank, brush it and have it clear coated for a nice raw look - see attached.  However I recently got inspired by a customers bike in Poland (the SR was a Police bike there for many years  ;D ).  His bike had the original tank in white and it had gained some really nice patina - the typical collection of grime around the filler cap, a few scratches and dings, then this really nice yellowish brown in some places where fuel had been spilled on it and it had weathered differently there.  This gave me the idea that perhaps I want to keep the original paint - it is kinda cool after all, in brilliant orange.  Plus it has a really stylish 'SR' on the sides.  Then I would reuse the stock headlight too, which also has some nice patina.  I then looked at one of my favorite bike books for some inspiration and yes, I really like the rough, old bike look - check out the cool Nougier Four.  Yes, I will need to 'cheat' in some places for some parts that are new, but I won't do anything special with them, just leave them uncleaned and unpolished and let time do it's work.  What are people thoughts on this idea?

It also leaves me with a dilemma of how to remove the one massive dent in the middle of the tank while retaining the paint... Anyone tried one of these kits?...

https://www.youtube.com/watch?v=NGT5Q7j4xnY
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: advCo on Feb 27, 2019, 16:23:38
The dent puller should work since its not bad and really no hard creases. You can also try a blood pressure gauge from the inside, inflate it to pop out the dent.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: wozza on Feb 27, 2019, 17:12:49
The cheaper kits dont really work on fuel tanks as the metals a little to thick...have tried and failed....
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: advCo on Feb 27, 2019, 17:32:27
You can also try getting a lever in there and pushing it out from behind. If you try this be sure to put a cushion on the end so you don't put a fresh crease in the metal from the back side.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Feb 27, 2019, 23:31:16
I tried a very similar hot-glue-gun-bridge device (Ding King brand) and it was so-so. Am following a guy on YouTube (Sweet Project Cars) and he had a couple episodes on using a slide hammer with hot-glue plastic pads. Was so impressed I got a set, but have not gotten around to using it. Many of the kits on ebay include hand or bridge pullers, but the slide hammer and plastic pads looks to be the best option.
I ended up doing the Virago 750 headlight mod to the OEM SR250 headlight ring to get a H4 replaceable bulb (we only got the weak sealed beam headlights in the USA). I think that had I to do it over, I would go with a 5 1/2" LED light assembly (think Daymaker).
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Brodie on Feb 27, 2019, 23:36:58
Crusty but trusty. I have quite a few bikes like that.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 03, 2019, 12:36:07
Crusty but trusty. I have quite a few bikes like that.

Haha I love it.  Exactly.

Thanks for all the tips and info!  I'll give the slide hammer version that zap mentioned a go.  Makes good sense!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 03, 2019, 12:48:06
I posted something on Instagram a couple of days ago about a header extension kit I am thinking of producing.  It lifts the silencer up to a 20 degree angle (matching the pillion peg bracket angle) to get more ground clearance and give a bit of a more sportier appearance.  It will clamp onto the existing Jadus header (or possible even the stock header).

For this build, I plan on using this extension to weld in a vacuum pick up for a PCV system.  On the third photo you see where the battery is positioned under the swing arm (the Jadus triangle tidy kit puts it there).  But for this build, with the elimination of the electric starter, the wire harness can be much simpler and therefor the battery too - so I have bought a 4 cell Antigravity instead of the 8 cell and the small battery will now sit under the seat in the electrics tray.  This then leaves space on the Jadus battery bracket for an oil catch can for the PCV system.

I have read a bit about this in Graham Bell's 'Four Stroke Performance' book and have a pretty good idea about how I will do it.  I have also read a bit online where people have had success with this system with thumpers - to combat the huge pumping losses.

Here is a great bit of info from zap a while ago in this very build thread:

'One thing to suggest to your list of engine mods is thinking about pumping losses. There was an article by Dave Searle in Motorcycle Consumer News about this a couple months ago. Thumpers are notorious here because they don't have other cylinders working together to offset the crankcase pumping action. Many builders just vent their crankcases to look "cool" but it really doesn't do anything to decrease pumping loss (just keeps oily junk out of the carb like an oil catch can would); I got a Krank Vent off evilbay to experiment with creating a partial vacuum in the crankcase instead of trying to get all that air in/out of that skinny hose outlet (still planning). Krank Vents are a 1-way check valve and seem to be very popular with the H-D crowd as they reduce crankcase pressure and keep gaskets from blowing. My thoughts are that the engine will pump through the Krank Vent a couple times until the partial vacuum is created, then no more pumping.'

Does anyone have a link to that dudes build thread where he made a similar system for an LS650?  (must be huge pumping losses in a 650 thumper!).
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 08, 2019, 07:16:34
Since I sorted the frame geometry/suspension set up (rear shocks ordered, more on that later), it was time to sort out the riding position.  The clip ons are not sitting 100% correct but pretty close.  They will drop about 20mm once I trim the top triple clamp.  But I will leave them there above the triple clamp rather than moving it down to between them.

So with the bars relatively set, the biggest task was to get the footpeg position right.  Which sounds pretty straight forward, but with not wanting to use the stock position (too low, too little ground clearance cornering) or the stock rear passenger peg position (too far back, too high, just awkward), I need to draw up a custom bracket.  But where to start?  I made a simple plywood template with a bunch or known/measured hole positions relative to the stock footpeg bolt positions.  After a a lot of playing around and 3 prototypes later (third proto printing now), I am pretty sure I got it right.  You can see the development in the images.  I wanted to get a comfortable position when crouched (and also aerodynamic-ish) plus a decent leg position when stopped at traffic lights etc.  This also worked out nice for a visual position with my knee right on the side of the tank where it should be.  To test all this I set the camera up on a tripod with a timer and took a bunch of shots with all the different positions - so I could study them and compare.  Don't laugh, I felt as ridiculous doing it as it looks haha  ;D

You can also see how much ground clearance there is at full lean (yeah right!!! haha).  The exhaust silencer will most likely be the bigger problem now, rather than the footpegs/my feet. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Brodie on Mar 08, 2019, 16:48:27
That is awesome. Totally sort out the cornering clearance issue the stock pegs create.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: jpmobius on Mar 08, 2019, 18:22:37
Not too sure where you are on the foot control levers, but going to pass a couple of things along early just in case.  First, and this may be obvious, the lever arm that pulls the brake rod needs to be at 90o or greater to the rod.  This looks to not be possible with the lever in your pics as you will want the pedal to be angled down considerably with the brake not being applied.  The actuating arm would need to be rotated anti-clockwise considerably to be in an appropriate range.  The second less obvious but potentially more important issue is the location in space of the pivot between the pull rod and the actuating lever.  Ideally, this would be directly coincident with the swing arm pivot.  In this location, movement of the suspension will not affect the action of the brake.  Moving away from this location in any direction will cause motion in the brake mechanism when the suspension moves.  Generally it is extremely inconvenient to locate the pivot in this ideal spot, but moving it rearward along a line between the SA pivot and the rear axle has only very minor impact.  You can not move the pivot up or down from this line very far at all without very noticeable "pumping" of the pedal as the suspension follows bumps in the road.  Move the pivot far enough and the brake can actually become applied with enough suspension movement - very bad!  One common solution is to use a cable like that used on the front which eliminates this problem completely, but is a lot more complex than the simple rod and lever scheme. 
Personally, I spend a LOT of time sorting out the riding position.  The person who will be riding the bike needs to spend at least 15 - 20 -30 minutes sitting on the bike, with the seat at the correct height, hands on the bars selected and adjusted, and feet on mock ups in the expected position.  That would be a pretty short ride, but will indicate if changes are wanted.  It does not factor in wind resistance, but in my experience, that is less important a factor on setting the ergonomics than is popularly thought.
Of course, getting the seat, bars and pegs just right with no concern for the associated machinery invariably makes for a lot of fabrication work to get all the controls to work equally well.  I think it is worth the effort to have a bike that is really comfortable and fits your purpose perfectly.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Mar 08, 2019, 19:09:27
Foot position you are exploring is way to tight for me, but I really like the upswept exhaust adapter idea! Gives the ability to clamp the exhaust way after the stock foot peg, improves the look a whole lot, and improves ground clearance.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: doc_rot on Mar 12, 2019, 04:55:05
If these are parts you plan on selling you might consider making the position adjustable somehow. I personally I never ride with the middle of my foot on the peg, only on the balls of my feet, so that position would be way too far back. Rizoma has some nice eccentric adjusters that look pretty good too. just my .02
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 14, 2019, 17:55:05
Thanks for the feedback!  This body and footpeg position would not be my choice for a daily rider or even a weekend thrasher,  but this build has pretty much one purpose, so I figured things could be pretty extreme.  Good point about making adjustable ones Doc.  I am not sure I would offer these to customers though - my products are already niche enough, let alone racer position footpegs haha.  I did try placing my toes/balls of my feet on the pegs though because I do that sometimes like you too.  These printed brackets and the plywood template were not quite strong enough to test that properly though.  Jp I'll respond to you below...
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 14, 2019, 18:00:12
Jp I spent a long while pondering the brake linkage.  The gear linkage is pretty straight forward but yes, the brake is more challenging.  I looked into all sorts of solutions, even converting to cable linkage instead.  But then I remembered I have a spare stock brake pedal that I can modify.  I think the following solution (see attached sketch) will work.  What do you think?  Hope it's clear enough, the proportions are not quite right but I think you get the gist...

And in your response to comfortable body/riding position.  I already assume this won't be comfortable  ;D  I'm going to make my daily rider much more back and wrist friendly though haha
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Mar 15, 2019, 07:57:32
Why have a setup with two levers doing the same work?   Can you not make it so that your rearset lever is pulling the brake linkage without the second lever?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: jpmobius on Mar 15, 2019, 10:15:17
That is a good solution.  The factory places the pull rod connection point at pretty much the only good spot, so incorporating the original portion can't go too far wrong.  It would be a good idea to consider the leverage of the oem setup as you will likely want to have similar effort required in the new setup.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 17, 2019, 06:53:29
That is a good solution.  The factory places the pull rod connection point at pretty much the only good spot, so incorporating the original portion can't go too far wrong.  It would be a good idea to consider the leverage of the oem setup as you will likely want to have similar effort required in the new setup.

Great, thanks.  I'll post a mock up as soon as I have one.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 17, 2019, 06:59:47
Why have a setup with two levers doing the same work?   Can you not make it so that your rearset lever is pulling the brake linkage without the second lever?

These were my exact thoughts in the beginning as well - why add mechanical complexity through an extra linkage?

Then it struck me in the middle of mocking up such a solution, then I confirmed my assumptions with google.  The answer is simple, you do not want a control lever attached to a moving part - the moving part being the swingarm.  The reason is twofold:  The action of the lever and its throw is no longer linear to the brake arm - because the angles and position of it change in relation to the brake lever through the rear suspension travel, plus, the required force also changes.  You would even run the risk of weird feeback through the brake lever as the suspension goes through its motion.

Just google any OEM rear set linkage solution (nowadays its mostly hydraulic disk brakes, but look at drum brakes) and you will find an interim linkage that disconnects swingarm to brake lever  ;)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Mar 17, 2019, 09:18:28
The real reason is that you want the lever pulling the brake drum at the swing arm pivot.  If your pedal is not that at the swing arm pivot then all that makes sense.  Not sure why that didn't occur to me when I asked the question.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 17, 2019, 11:37:35
Yes that makes sense too.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 18, 2019, 04:21:28
On another note, I got my Antigravity small case 4 cell battery over the weekend.  This will fit nicely under the seat  8)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 18, 2019, 09:49:21
https://hobbyking.com/en_us/turnigy-5000mah-4s1p-14-8v-20c-hardcase-pack-1.html

Thatís the battery I use in my RD.

Iíve also used a pack half that size.

With the large pack, if it starts within in a minute of kicking itís good to go. I wish I had gone for a modern charging system though. Getting rid of that excited coil system would have saved me another couple of pounds.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: killerx on Mar 18, 2019, 16:13:19
if you use a cable to actuate the rear brake, the cable becomes the "disconnect" between the pedal and the swingarm motion.
just like the hose on a hydraulis set-up.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: wozza on Mar 18, 2019, 21:33:42
https://hobbyking.com/en_us/turnigy-5000mah-4s1p-14-8v-20c-hardcase-pack-1.html

Thatís the battery I use in my RD.

Iíve also used a pack half that size.

With the large pack, if it starts within in a minute of kicking itís good to go. I wish I had gone for a modern charging system though. Getting rid of that excited coil system would have saved me another couple of pounds.
That battery isnt suited to bike use unless you have a balance charger setup...the antigravity one has basic electronics to prevent over/under charging and keeps the packs balanced....Only issue Ive found with the gravity batts is, if there is a tiny drain the protection circuit wont cut the power before a cell drops to low killing the battery..so if sitting for a long time disco the battery.I use a Anderson 50A connector https://www.jaycar.com.au/anderson-50a-power-connector-6-gauge-contacts/p/PT4420  to quick disconnect the power should I park it for a while or for emergency disco if it all go's bad :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 19, 2019, 04:19:02
Thanks for the tip wozza, that has actually happened to me (an antigravity go too low and die).  So I will do that for sure.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 19, 2019, 13:27:25
That battery isnt suited to bike use unless you have a balance charger setup...the antigravity one has basic electronics to prevent over/under charging and keeps the packs balanced....Only issue Ive found with the gravity batts is, if there is a tiny drain the protection circuit wont cut the power before a cell drops to low killing the battery..so if sitting for a long time disco the battery.I use a Anderson 50A connector https://www.jaycar.com.au/anderson-50a-power-connector-6-gauge-contacts/p/PT4420  to quick disconnect the power should I park it for a while or for emergency disco if it all go's bad :)

If I had a nickel for every time somebody lectured me on batteries Iíd have some serious change.

I ran a low voltage disconnect for quite a long time and I have logged each cell voltage over several thousands of miles. I recorded them at 1hz, but also recorded total V as well. I concluded that as long as I didnít have issues starting or a failing charging system that the low voltage disconnect wasnít needed. Sure it would likely ruin the battery if I pulled the cells under 2.5V, but at $30 for a battery who cares? As far as balance charging, thereís never been a need. The cells have always remained very consistent and balanced. I do have a balance charger that I can if I need balance the cells, but it hasnít been out of the tool box in two years. Even the 2500mah battery works just fine. I have converted my regulator and rectifier to solid state units, but thatís recommended for all modern battery chemistryís.

All of the said, battery management circuits can be had for like $6. Combined with the battery i posted you have the equivalent of the Antigravity but at a massive cost savings. Finally, Iíll add that Antigravcity batteries a few years back were not managed, they pitched their overpriced RC car battery charger to all their customers. In summary, if you know what you are doing my battery is absolutely suited to bike use.

Quick edit: Iíll add that my low voltage disconnect was automatic, not plugging or unplugging required. Also, my RD draws less than 5 amps, but it will charge at nearly 6amps, so I end up running a 10amp fuse. With that in mind, a 50amp plug is an absolutely silly sized plug for a motorcycle, itís what we use to jump 2 liter formula cars.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 19, 2019, 13:52:57
One additional note, while the price advantage of the RC battery is nice the main advantage is packaging. I didnít like the dimensions of the AG battery within the packaging constraints of my build, those were rather considerable but resulted in a 270lbs RD350.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: wozza on Mar 19, 2019, 18:50:55
Meh each to their own....sounds like you have it sorted......I prefer a simple elegant solution as cost isnt always a factor for me ...anyway getting off topic sorry OP;)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Mar 19, 2019, 23:24:01
After killing a few lithium ion batteries I decided to start taking them apart only to realize they are pretty much the same thing in different packages.  For many of them, like the Shorai, there's half a plastic box of dead space.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 19, 2019, 23:39:17
Yep, they come from a few different sources. Certainly a lot of back end science, but at the end of the day there's not too much difference as the state of the art is what it is.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: wozza on Mar 20, 2019, 01:00:20
once again to the OP sorry..but I have to point out whilst you have done your homework and come up with a cheaper option...My concern is some young/old uninformed person see's the link and think yeah thats cheap and throws it in their bike and isnt as lucky as you....also your insurance may not cover any damage .
Finally I have been flying RC for over 40 years and currently have about 30 lipos sitting here in a metal ammo case, Ive seen far to many of the hobby king ones puff and fail even with the best charger and most care.....All the power to you for thinking outside the box but not all of us are that smart :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 20, 2019, 04:06:09
Agreed.  Seems like you know your stuff in this area and I would be happy if I did too, but I don't.  For average Joe home mechanic (me included) I wouldn't be confident installing stuff I don't understand.  But knowledge is power and more power to those who can!  It's awesome that most builders excel at something on their bike from either their trade or profession.

I think your solution is cool though savor!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 20, 2019, 04:22:53
To change the subject a little...  I received my custom built YSS shocks yesterday - super cool.  I had searched and searched online to find shocks that suited - there are many shocks with the correct eye dimensions and the length I wanted, but not spring rate, that is harder to find.  I had been in touch with YSS customer support and Hagons as well.  As mentioned in a previous post, Hagons have good customer service and can custom make shocks, but they just look so damn ugly! That's just a personal taste thing but I think their product development and production needs to lift themselves out of the 60's.  They have one new promising range of shocks - the Nitro range, but they are super pricey.

Anyway, I settled on YSS because they were also super helpful and could build a custom shock.  They also look great and are great quality.  Check em!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 20, 2019, 04:30:16
And if anyone is interested, here are some specs...

Stock:

295mm Eye to eye
14mm Top eye
14mm Bottom eye
14-20 Spring


YSS Custom:

RE302-T - Aluminium
340mm Eye to eye
14mm Top eye
14mm Bottom eye
13-18 Spring (lighter rate for lighter bike and skinny rider)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Mar 20, 2019, 15:13:48
Just curious - what are the spring rate measurement values?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 21, 2019, 04:34:07
Manual states:

K1 = 1.4kg/mm (0-50mm)
K2 = 2.0kg/mm (50-70mm)

I guess it is more common to write 14-20kg.  Which would be kg/cm?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 21, 2019, 18:37:10
The K1 will get you close, but the K2 section is over sprung. You should be able to get away with zero preload, but you might immediately be in the k2 range.

I run 75lbs/inch straight rate on my RD and k1 works out to around 78lbs/inch. Your machine ideally will be significantly lighter.

YSS makes great stuff, but I'm not sure you are quite right with those rates. Assuming they are standard size springs the sky really is the limit though.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 21, 2019, 18:47:55
I built a spring rate estimator that helps dial in the ball park figures. I apologize that it's in imperial units only.

http://chrislivengood.net/wp/advanced-spring-rate-estimator-new/
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 22, 2019, 10:03:02
The K1 will get you close, but the K2 section is over sprung. You should be able to get away with zero preload, but you might immediately be in the k2 range.

I run 75lbs/inch straight rate on my RD and k1 works out to around 78lbs/inch. Your machine ideally will be significantly lighter.

YSS makes great stuff, but I'm not sure you are quite right with those rates. Assuming they are standard size springs the sky really is the limit though.

Interesting.  So I would be better to have a 14-16?  Or a 12-16?  This is what YSS suggested and I hope they have the experience to give that advice based on bike and rider weight.  This is what customer support from Hagons said:  'We can do an equivalent shock to stock but ours is normally sprung and damped better. More like 16kg-20kg instead of 14-20kg.'
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 22, 2019, 13:08:32
There is a lot of room for interpretation and preference. I'd say you have a really good starting place.

Basically every build will go stiffer over stock because people are heavier today and they wear more gear. That is true right up until you spend a lot of time and effort building a bike that is significantly lighter than stock. At this point you are at the mercy of those selling stuff or at a minimum your own experience and testing.

My personal preference is to run very little preload, run a spring that is the right stiffness to achieve 30% sag, and then let the damper provide platform stability but be digressive from there. I'm not sure what YSS are up to, I haven't dyno'd their shocks, but based solely on spring rate you aren't far off. So give a ride and see how it works. I know you've spent a lot of time on the front as well.

I'm not trying to derail you here, I love your build and have followed it very closely from the get go as it reminds me a lot of my RD build.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 23, 2019, 14:16:39
There is a lot of room for interpretation and preference. I'd say you have a really good starting place.

That's good to hear!  I see on your webpage how much you have worked/work with suspension and it's impressive stuff.  I think some trial and error will be needed in this case as well.  But I am such an incompetent rider, I don't think I would know/feel what is good or not  :-[
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 25, 2019, 08:40:36
I have been searching around for a titanium fastener supplier for some time now and have received quotes from 3 different companies.  The idea was to be able to offer an engine bolt kit in silver, black and gold - to suit different customers tastes.  I knew Ti was expensive but not so expensive as the quotes revealed!  I've canned this idea to offer customers, but I did order a sample set to see the weight difference and check the quality.  Added bonus is that this set can be used on this bike!  170g lost weight just with some bolts  ;D haha 

The coolest thing to do would be to draw up the front and rear wheel spindles and have them turned up in Ti - to reduce unsprung mass.  But that is not within the scope for this project, both in terms of time and money $$$$$$
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 25, 2019, 09:40:53
If you have a lathe you can center drill bolts. You'll gain nearly what you do with ti but do so at a fraction of the cost. The reduction in strength is nearly zero for center drilling, it's just a timely process. I know there are aircraft bolts that you can buy center drilled as well.

Ti hubs would be incredible, but you might end up with brake rotor over heating has ti isn't a good conductor of heat. Magnesium might be a better choice.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: teazer on Mar 25, 2019, 18:05:56
Making axles out of Ti has been an effective way to reduce weight for a long time, but always more than my budget would stand.  Most axles and other bolts can be drilled down the center to deduce weight and it's not hard to lose 20-30% of the weight that way.  You could add Ti retaining nuts to save a few more grams.

BTW, many drag racers use aluminum front axles.  Yes you heard that right.  I would not recommend those for street use, but it's a thing.

On our RD350 drag bike, I bought a GSXR lower triple clamp quite cheaply and had it machined to replace the stock steel one and that saved a huge amount of weight. A lower triple machined from billet would have been nice or maybe even a TZ250 lower triple in aluminum with Ti bolts would have been nice but not available within our price range.

You could replace every bolt and stud on the motor with Ti but the cost would be off the charts expensive.  There are easier and most cost effective ways to lose weight, such as plastic or fiberglass or alloy components for seats, and spacers and wheel bearing spacers - as long as you have access to a machine shop.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Mar 25, 2019, 20:39:27
Making axles out of Ti has been an effective way to reduce weight for a long time, but always more than my budget would stand.  Most axles and other bolts can be drilled down the center to deduce weight and it's not hard to lose 20-30% of the weight that way.  You could add Ti retaining nuts to save a few more grams.

BTW, many drag racers use aluminum front axles.  Yes you heard that right.  I would not recommend those for street use, but it's a thing.

On our RD350 drag bike, I bought a GSXR lower triple clamp quite cheaply and had it machined to replace the stock steel one and that saved a huge amount of weight. A lower triple machined from billet would have been nice or maybe even a TZ250 lower triple in aluminum with Ti bolts would have been nice but not available within our price range.

You could replace every bolt and stud on the motor with Ti but the cost would be off the charts expensive.  There are easier and most cost effective ways to lose weight, such as plastic or fiberglass or alloy components for seats, and spacers and wheel bearing spacers - as long as you have access to a machine shop.
There's a story about Nick Richichi having a buddy who machined Ti axles for his TZ750 and after the first practice lap he told his guys to take them out.  The flex made turning sluggish, since it added flex to the forks.  I imagine aluminum would do similar being it's 1/3 the stiffness of chromoly.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 26, 2019, 06:02:13
Interesting discussion!  Ti is just astronomically expensive and is perhaps best reserved for dedicated racing machines.  But center drilling the axles would be more feasible.

doc_rot did something interesting here:

http://www.dotheton.com/forum/index.php?topic=66016.380 - scroll to page 39.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Mar 26, 2019, 12:07:54
On my RD I went up to a 17mm axle and center bored it. It's definitely light. I used stainless, I forget which grade.

I'm not sure what size axle the TZ ran, but if steel was fine and Ti wasn't I have a hard time believing axle flex was actually the issue, now if the axles didn't have proper clearances or perhaps tensioning that change in feel could very well be the case. Slop and flex I believe are often conflated, whether it be from a results perspective or overlooked during theoretical discussion. When I was working on the numbers for my front axle it was pretty clear that axle diameter after a certain D would not be a significant effective increase in stiffness given the loads the axle sees, from memory I believe diminishing returns started at like 10mm. Even from 14mm stock to 17mm modified there just isn't enough load for it to make a difference. Where the real gains are made though is in the fit of the various components to the axle. And to be clear, a larger D at the fork fixings and the resulting increase in bearing area did aid stiffness, but the beam strength of the axle wasn't a factor. Ideally the axle would be a light press fit in the wheel bearings and then the axle clamped and tensioned in the forks. A nice tight no slop fit in my simulations created the biggest gains in deflection resistance, and tensioning was the icing on the cake. Getting this all right would create the most taught feel. All of that said, I tend to believe that the damping properties of various materials and alloys to be just as important as Young's modulus, this in large part is why we don't see more carbon fiber frames even at the highest levels. That and when chassis systems as a whole become stiffer generally their tuning window tends to narrow making them less friendly to keep inside peak operating conditions. 

Anyways... center drilling is a good affordable solution especially if a lathe is available.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Mar 28, 2019, 08:52:22
When designing the rear set brackets I was hoping I could use some rearsets I had over from an abandoned project years ago.  They would have worked if I were not converting to kickstart, but because I am, they would get in the way.  So I found these other cool folding ones on ebay for a great price and the quality is actually outstanding.  I think I will still need to heat and bend the kickstart lever slightly for clearance, or order the wider RD400 kickstart lever.  The old rearsets will get saved for a rainy day project  ;D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 01, 2019, 03:05:47
I found it!  I knew I had read somewhere in one of my speed books about the PCV system connected to exhaust rather than intake - see attached.  Also, this other extract below is taken, believe it or not, from the Wikipedia page about PCV valves: 

'Not all petrol engines have PCV valves. Dragsters sometimes use a scavenger system and venturi tube in the exhaust to draw out combustion gases and maintain a small amount of vacuum in the crankcase to prevent oil leaks on to the race track.'
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Apr 01, 2019, 12:19:38
I had heard of exhaust-induced depressurization before but I don't see the benefit (vs cost/complexity) of using this system over the intake-induced depressurization 1-way valve I mentioned much earlier. Any references speak to both and cite the reasons for the preference?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Apr 01, 2019, 14:09:50
Your crankcase already vents to atmosphere, or in stock form to the air box.  Draw through the airbox helps produce vacuum similar to the way a pcv works, which draws from an intake.  Using the exhaust is a pretty common, pre-pcv, old school way of doing it on V8s.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Apr 01, 2019, 18:43:19
Your crankcase already vents to atmosphere, or in stock form to the air box.  Draw through the airbox helps produce vacuum similar to the way a pcv works, which draws from an intake.  Using the exhaust is a pretty common, pre-pcv, old school way of doing it on V8s.
Right - except that vacuum is only present in the crankcase when the piston is moving upward; otherwise it is a series of push-pull movements which is the windage loss described. My previous suggestion was to use a 1-way Krankvent (used by the H-D crowd for the same reason) in the OEM line going from crankcase to intake so as to create a vacuum in the crankcase. I didn't know if Jadus' research had uncovered if the exhaust-induced vacuum method was better or...
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Apr 01, 2019, 23:48:30
Right - except that vacuum is only present in the crankcase when the piston is moving upward; otherwise it is a series of push-pull movements which is the windage loss described. My previous suggestion was to use a 1-way Krankvent (used by the H-D crowd for the same reason) in the OEM line going from crankcase to intake so as to create a vacuum in the crankcase. I didn't know if Jadus' research had uncovered if the exhaust-induced vacuum method was better or...
Smart.  I hadn't though of running a Krank Vent on a jap bike.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 02, 2019, 03:11:45
Good points.  I haven't drawn any conclusions, only that the stock system (and many other jap bike systems for that matter) are sub optimal because they draw up a certain amount of oil mist from the crank cases into the engine - affecting combustion and having many negative affects on power and engine wear.  Tapping into the exhaust just sounded like a good way to avoid this entirely.  But with the addition of a valve, I struggle to see the benefits over the intake pick up?  Why would dragsters and many race cars hook into the exhaust instead?

Using the exhaust is a pretty common, pre-pcv, old school way of doing it on V8s.

I like!  Seems simple and obviously worked decent enough for years until better systems were made. 

Think I'll still use a valve though, otherwise there'll be a bunch of burnt oil mist in the exhaust...
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: stroker crazy on Apr 02, 2019, 05:26:25
otherwise there'll be a bunch of burnt oil mist in the exhaust...

That could be a plus for two-stroke fans!

Crazy
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 05, 2019, 03:45:08
Yesterday evening was pretty exciting for me!  Received the first prototypes of the adjustable fork caps I have designed.  They look and feel top notch!  They installed flawlessly as well.  Just a couple of adjustments to make the covering cap (completely cosmetic and non-functioning) stay in place better (it works its way upwards over time).

I took a couple of shots of how the assembly looks and what it is like to install it as well.  A damn site easier than the stupid system from the factory.  Did they do it like this to make it difficult for customers/owners to mess with the forks themselves?  So it required special tools/knowledge to get into them?

I ordered 3 sets, one goes on the daily rider for immediate testing, one set is for this project and the last set is for a test house or a competent workshop with a large press and digital load read out that can log data.  They will be both load/stress (max until deformation detected) tested and spike tested (hit suddenly with a certain force) several times.  I also have a colleague who is very capable with FEA software who is running some simulations for me.  Basically, I am extremely paranoid about the safety of these - very little for my own safety (because I personally trust the engineering) but a boat load for the market/potential customers/users.  So to have some safety data on them is critical!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Apr 05, 2019, 07:49:42
Beautiful.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Jimbonaut on Apr 05, 2019, 10:34:25
My thoughts exactly
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Maritime on Apr 05, 2019, 13:14:21
Very slick.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 11, 2019, 07:53:08
Cheers guys.  Looking forward to the test results.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 11, 2019, 08:01:19
Now I am measuring up everything to draw up some custom swingarm bushes.  I looked into roller cage bearings as well and correct sizes are available but from what I've read, they do not bring any benefits to the table.  Or is there something I am missing?

If I draw up the bushings, I should then also draw up some custom inserts as well right?  In stainless steel so they don't corrode? 

I am also looking into what I can do about the seals - something better than the stock ones that obviously allow crap to come in.

Just look at the wear from the stock bushings  :o
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on Apr 11, 2019, 09:06:24
 A bronze bushing has a much higher load rating, but they have a tendency to oval and develop slop over time.  This is why most dirt bikes have gone to needle bearings.  The load rating on a good SKF type needle bearing, though, is going to be way more than what will ever be experienced on most any motorcycle.  So essentially, a good needle bearing will be practically maintenance free for a really long time.  They can be bought with a port drilled in the jacket to be lined up with a zerk fitting for the occasional greasing. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Apr 12, 2019, 04:21:55
Thanks for the input.  Perhaps I should revisit this.  It is after all easier and should be cheaper (standard items vs custom machined).  The machined parts would cost a lot as well based on the necessary tight tolerances.

I noticed when looking for bearings that there is often seals that go with them/seals that suit the bores the bearings are designed for.  Then I just need to have some spacers machined up to control the placement depths of the bearings each side of insertion, plus some spacers to take up the missing space of the weird stock seals (if I find other ones that I think are better).  The stock ones are some kind of cap seal solution which seams unnecessary if a good internal seal is installed.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Apr 12, 2019, 11:47:21
Just food for thought, but I always wanted to use some preloaded angular contact bearings, similar to what is used in automobile uprights. They are sealed and can handle side loads as well as vertical. Would be perfect for a swingarm, the only down side might be their size. Needle bearings are such a bastard to keep clean and smooth functioning, at least they have been all of my MX bikes. It's probably less of an issue on a road going bike.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Apr 12, 2019, 12:06:39
A bronze bushing has a much higher load rating, but they have a tendency to oval and develop slop over time.  This is why most dirt bikes have gone to needle bearings.  The load rating on a good SKF type needle bearing, though, is going to be way more than what will ever be experienced on most any motorcycle.  So essentially, a good needle bearing will be practically maintenance free for a really long time.  They can be bought with a port drilled in the jacket to be lined up with a zerk fitting for the occasional greasing.
I know that the XS650 originally came with plastic bushings in the swingarm and Mike's XS has sold quite a few bronze replacement kits.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Apr 12, 2019, 15:25:30
Same with the RD's, plastic bushings OEM.

I have a set of Mike's bronze bushings and they work a treat, the price is good too.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 09, 2019, 04:44:47
Received these brackets the other day after getting back from holiday.  Now onto making the linkages!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: advCo on May 09, 2019, 09:26:12
Those look killer. Nice work!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 27, 2019, 04:45:03
Been scratching my head over the brake linkage over the weekend.  I could get this set up to work really well I think (the pictures don't show what the optimal/final angles would be) but I am not sure I want to go down this path...  It seems to add a lot of weight and complexity to the bike and operation.  If I went with a direct connection the the brake arm I could remove the bracket under the frame and lose some weight there, plus the pivot shaft and the steel bracket that I would weld up (mocked up in the images).

So back to a few posts ago...  How poorly would a direct connection perform?  I know @irk miller wondered the same thing.  It also seems there have been people before me have done this and succeeded.  Even Ryca with their cafe racer kit for the LS650 Savage do it - post to follow.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 27, 2019, 04:51:47
Heres just a couple of examples.

Failing this as an alternative, I have one other option.  That would be to design a bracket that rotates around the swingarm pivot itself.  I would draw up a bracket to be machined in aluminium that goes over the swingarms welded pivot shaft.  Might need to let this brew in my head for a while.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Brodie on May 27, 2019, 06:05:28
Just to through another spanner in... Have you thought about using a hydraulic slave cylinder to pull the rear brake actuator and a small master up near the reset? Might weigh similar to all the steel there for the stock setup.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Karlloss on May 27, 2019, 07:59:43
This is a conundrum I am facing on my project, I am thinking of using a pull type hydraulic slave cylinder as suggested. Plenty available on eBay.

If you do use it, I'd be interested on how you get on with it.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: teazer on May 27, 2019, 09:42:32
We used a similar linkage on our first CB160 Vintage race bike.  It worked fine but too complicated by far. So then we moved the cable mount and used a straight cable run.

In fact there is a cable conversion for the RD350 that looks like it would be perfect for your needs without reinventing the wheel.

Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: irk miller on May 27, 2019, 10:41:19
I like to run a cable setup for rear sets on the drum rear wheels.  This is one of designs I've been emanating over the years:

(http://www.dotheton.com/forum/index.php?action=dlattach;topic=56913.0;attach=114736;image)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: pidjones on May 27, 2019, 17:47:52
Yep, seems a cable setup would be lighter and less complicated.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 28, 2019, 03:35:21
Yeah through my searches I came across the following set ups...  Hydraulic set us included.  This is one of the cleanest I have seen.  Then there is a budget version I saw as well - probably works just as good, just looks a little ratty.

Has anyone tried the DCC kit?  https://www.dimecitycycles.com/dcc-customs-rear-brake-cable-conversion-kit.html
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 28, 2019, 03:40:00
So no one is thinking the direct mechanical linkage is a good idea? 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: stroker crazy on May 28, 2019, 03:48:05
So no one is thinking the direct mechanical linkage is a good idea?
I can't see why it wouldn't work.

There's one way to find out ...

Crazy
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: SONIC. on May 28, 2019, 10:19:11
The direct mechanical linkage is fine, but I don't like the bends in the linkage rods. The more force you apply the more you're going to lose to that bar straightening out instead of applying your brake.
The rod is supposed to be in tension, so when it's a straight rod it applies the full pressure to the brakes. When bent like that sure it clears the exhaust but the forces are all wrong, you're trying to straighten the rod and apply the brakes at the same time. Worst case is in a panic you stomp the brake and the rod just straightens out, the next time you apply the brakes you don't have any.

Same goes for using the rod to "push" the brakes, it works and I see it done, but in a panic it's going to bend and you're screwed.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: teazer on May 28, 2019, 12:06:34
That TZ rear wheel that Irk posted is the tidiest and more or less how I set up an R5/RD350 rear brake. I had the rear brake plate welded to create an abutment for the cable rather than making a steel one to bolt on and I used a Suzuki T500 or GT750 cable.  That was on a TD3 so it already came with cable ends at the front. 

http://pinkpossum.com/td3/images/DSCN1724.JPG

http://pinkpossum.com/td3/images/Copy%20of%20DSCN1196.jpg

That's what makes that DCC kit interesting.  I'd seriously look at that as a design idea.

Those hydraulic arrangements are interesting but add complexity and cost and weight.  The best set up is a cable IMHO.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: pidjones on May 28, 2019, 17:38:36
Note that with the pull to the bottom, if anything should happen to your stay rod, the drum will rotate pulling the rear brake into full lock. Not fun at 65 mph on Folly Beach road!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 28, 2019, 17:41:42
That's a really nice set up teazer!

I looked really hard at the DCC kit and almost bought it.  But after watching their video about it: https://www.youtube.com/watch?v=M0PnjaZJicQ
I decided not to.  It is really a glorified clutch cable and the negatives is that it is really geared to Hondas and/or bikes with a stay that positions and holds the rear drum brake in place.  Which makes sense I guess.  But the SR has a slot in the drum brake plate that slide onto a boss on the swing arm.  I am not capable of welding aluminium so I am looking at more of a machined or bent type part to do this.

Then I looked at the stock set up again - see attached.  This set up is also a 'direct link' to the foot.  The pedal goes to the pivot shaft and then there is a flange up to the point where the brake rod connects.  In the case of connecting a brake rod directly to the rear set pedal, the only difference would be a slightly more offset rotation point for the pivoting of the brake rod in the pedal itself (swing arm movement), plus as SONIC mentioned, the tendency for the rod to want to 'straighten' itself under heavy loads.  To combat this, an extra stiff rod could be used.  But I have the feeling a M6 threaded rod with a matching aluminium tube/sleeve, together, will form a decently strong connection.  The actual offset that needs to be bent up doesn't seem all that bad either.

I think I'll try this method and If I hate the feedback or the movement in the pedal from swingarm movement, I'll go the cable route but make up something myself from an SR250 clutch cable and SR250 clutch cable bracket - it even already has the cable clevis! 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 28, 2019, 17:44:17
Note that with the pull to the bottom, if anything should happen to your stay rod, the drum will rotate pulling the rear brake into full lock. Not fun at 65 mph on Folly Beach road!

True, but as mentioned above, the SR does not have a stay like most other bikes.  Besides, there will be a mechanical stop for the pedal as well . to hold against the spring pressure which returns the brake arm.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: pidjones on May 28, 2019, 17:47:17
True, but as mentioned above, the SR does not have a stay like most other bikes.  Besides, there will be a mechanical stop for the pedal as well . to hold against the spring pressure which returns the brake arm.
I still prefer it running above the axle like these last photos show. Still have a big scar on my left knee from '75.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: SONIC. on May 28, 2019, 17:53:00
That looks about right right there!
I think a small bend to get around the frame there should be fine. You could also turn up an oversize stud and bolt one end to the inside of the pivot and the other to the brake rod to offset around the tube. Not sure which would be a better choice honestly.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: teazer on May 28, 2019, 19:18:58
That would work.  Might be better if the linkage were machined in a stepped shape to allow the actuating rod to be straight.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: crazypj on May 28, 2019, 20:15:06
Those linkage angles are terrible, the arms should be more or less parallel. Pic is my 360 before bending up a link rod
  As 'We' had a 1960's BSA C15 250 pulling  115 mph around 1974.  A 100 mph OHC motor should be easiy? Factory modified C15 only made 17bhp but at the time there were tuning parts from America available (1989 XR200 could be made to put out 22bhp, 24 bhp with Wiseco 'kit but then didn't last very long)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 29, 2019, 03:47:20
Those linkage angles are terrible, the arms should be more or less parallel. Pic is my 360 before bending up a link rod
 
True.  The angles will be adjusted for optimum mechanical work.  This was just a mock up.  Thanks for the pic, looks like a good set up - a bit like my first idea/intention!

As 'We' had a 1960's BSA C15 250 pulling  115 mph around 1974.  A 100 mph OHC motor should be easy?
  That is encouraging!  I hope so!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on May 29, 2019, 03:49:31
That would work.  Might be better if the linkage were machined in a stepped shape to allow the actuating rod to be straight.


Exactly.  I figure if I am going to be drawing up a custom linkage for the rearset (to create mounting points for the return spring and the brake light switch on the underside), I may as well include some smart geometry to reduce the offset in the z axis.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 02, 2019, 13:26:27
Over the weekend I managed to find some stainless threaded rod at a local hardware store, plus some stainless tube that fits it exactly - a little bit like the kits you can get from DCC or Lowbrow customs - except they come with alloy tube.

I think this will do the trick - should be well strong enough.  Also, in the last pic, you see the linkage bracket that I will redesign to include some of the required offset plus a spring connection on the underside.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: MiniatureNinja on Jun 02, 2019, 14:10:40
out of curiosity, why go with stainless tube if you're concerned with weight, I imagine it's almost 3x as heavy even if it's not much. also - I used carbon fiber tube on my brake actuation rod for my bike, it's stronger than the alloy - nearly impossible to bend and took quite a bit to break in the harbor freight press.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 02, 2019, 15:37:09
out of curiosity, why go with stainless tube if you're concerned with weight, I imagine it's almost 3x as heavy even if it's not much. also - I used carbon fiber tube on my brake actuation rod for my bike, it's stronger than the alloy - nearly impossible to bend and took quite a bit to break in the harbor freight press.

Carbon fiber would only work if the rod could be completely straight - I need two bends in this case.  Unless you laid up the carbon yourself to the shape/bends you wanted?

The stainless is heavier yes, but by very little - it has a 1mm wall thickness as opposed to the aluminium tubes 1.5mm wall - which evens out the weight diff a lot.  I figure I want this linkage to be strong and because this rod will save at least 500g over the original linkage idea (with two rods plus a linkage arm, plus a pivot axle). 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: crazypj on Jun 02, 2019, 15:42:11
LOL, Carbon fiber is too expensive for me but I would love to use it if I had enough cash. I used stainless link rod on mine as  I had some stainless bar and it's way stronger than 6061. A 6061 link is pretty ugly in a size that doesn't flex too much but for a torque arm isn't too bad in tension. I'm finally in the process of completely re-doing 360 (378)  Chassis weight is only a disadvantage for acceleration or up hill, SR isn't going to be too worried about a few extra pounds cornering (unless it's in a top box way high and way out back)
Sorry to burst your bubble but a more realistic number for an SR250 motor is going to be 20bhp until you spend mega money and even then 25bhp will probably be 'top' number' It's great fun to learn tuning on a single but even buying just one of everything gets expensive when you start breaking stuff. You will need a 'race' cam, probably modified rockers, oversize valves, lot of flow bench time (couple of spare heads needed) forged piston and probably a connecting rod upgrade unless you can get forged pistonway lighter than stock.You'll also need some math to do inertia and stress comparisons (cheaper than breaking stuff) It cost around $3,000 to get 24bhp from a Honda XR200 (about 7bhp over claimed output, nearer 11bhp in reality), 'flash dyno reading and then rod snapped. The 200 was 'quite reliable' at 22bhp, the extra 2bhp needed just a few too many rpm. I think I could have removed enough weight from piston and gudgeon pin but development stopped at 22 with some reliability and 'bolt on parts' that didn't require extra machine work.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 06, 2019, 15:03:23
Thanks for your input crazy.  You might be right about the power, but we'll see how things go with the mods I have done - many of which are ones you mention and are already done.

Also true about the weight reduction.  A lot of the small stuff I do now won't help with top speed or handling really.  But I must admit it has become a bit of an obsession so I may as well run with it until I run out of energy or funds or time, whichever comes first.  It's challenging and fun.

Just as a side not, the intake and exhaust system I designed for these engines gives a 20% power boost - this is verified on two different dynos, different days, different operators.  So to get 50% more power with a lot (a lot) of work just may be possible.  Heres to trying ;)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 06, 2019, 15:07:28
I decided to buy in the needed electrical stuff to complete the project - so I can start planning the wiring as well.  There were a bunch of speedo's I looked into but the Velona 80 from Daytona has a rev counter and idiot lights as well - no need for any extra dash items, nice. 

The blinkers I have used on another couple of bikes and really like them - they are super bright and small and only cost 30Euro a set.  They are exactly the same as other ones online for 70Euro a set, just that these are bought in bulk by Biltema so can be sold at this price point.

The tail light I am not so sure about but it is growing on me.  I like the size and the fact that the underside shines clear onto the license plate.

Hopefully get some time in the workshop over the coming weekend!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: Sav0r on Jun 06, 2019, 15:28:30
Looking good, my dude. Keep up the great work.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: crazypj on Jun 06, 2019, 19:24:03
Cool stuff designing exhaust system. OEM is always compromised by rules and regulations plus having something that will fit. In my experience a design that gives a power boost always acts as an amplifier at working rpm.  Quieting it down  doesn't automatically mean a lot less power though
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 14, 2019, 12:16:29
Did a bunch of stuff over the weekend (last weekend) and just posting now.  I tried making my own slide hammer to pull the tank dent - by gluing the end to the dent and hammering.  Failed miserably.  Lots of things wrong with it.  Anyway, decided to order a dent puller kit from ebay for 8gbp, be interesting to see if it works.

I also prototyped the rearset linkage bracket a couple times and think it will work good.  Managed to get in all the details it will need plus a nice 25mm offset so the linkage rod doesn't have to be bent so much.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: SONIC. on Jun 14, 2019, 13:34:17
Nicely done!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: jpmobius on Jun 14, 2019, 16:50:00
 Having plowed a fair bit of this ground myself, I have a couple of observations.  There is a lot to be said for a linkage system, but there is a requirement that is often so difficult to meet that a cable starts looking very appealing.  The issue is a result of the suspension motion.  In order for the action of the pull rod to be constant while the suspension moves, the pivot point where the crank arm connects to the pull (or push) rod must be coincident with the swing arm pivot.  Any other location introduces undesirable motion into the braking system as the suspension moves.  Obviously this is impossible to achieve, as the pivot is not stationary, and can only be ideal at one brake pedal location.  Fortunately, the problem is a matter of degree, so as long as the problem is small enough so as to be (mostly) unnoticeable, it is not a problem.  Unfortunately, there is a quite limited range of locations for this pivot where this problem is, well, not a problem.  The stock location is pretty much the only good place.  On virtually all bikes, you will find this location as close to the swing arm pivot as practical,  and very close to or on, a line drawn between the swing arm pivot and the rear axle.  Even very small deviations from this location will create obvious problems with the brake actuation as the suspension moves, though the seriousness of the problem often depends on who you ask.  Moving this pivot point fore and aft along the center to center line is fairly benign.  Moving it up or down off of this line is not.  Your location is high enough to be very noticeable to your foot if you apply the brake and have substantial suspension motion at the same time.  Opinions vary.  On a street bike it might only be an annoyance,  but it would be intolerable on a road race bike. The farther away from the center to center line, the worse this will be, and if far enough away combined with sufficient suspension travel, it is even possible to lock the brake even with zero pedal on a hard enough bump.
You can see how this works by taking off your shocks and while observing your brake pedal, moving your suspension up and down.  You will have to first adjust your brake to be off of its return stop to see the motion.  In operation, with the brake applied, you will feel the mechanism "pumping" as you travel over bumps.  This phenomenon is present in ALL similar mechanisms, even stock configurations, but it is small enough that it is unimportant.
From the pics, it looks like you can lower this pivot to fall along the center to center line, in which case the issue will become insignificant.  When I put a bike together, I determine where the pegs need to be and that is where they stay.  If you are committed to the current peg location, keep in mind that the brake pedal axle need not be part of the peg.  And if you have not already given consideration, the lever ratios are very important.  It is very useful to measure the stock brake pedal length, along with the length of the lever that connects to the pull rod.  You will need to keep this ratio, as well as the ratio between the lengths of arms at both ends of the pull rod in your new system if you want similar power required at the pedal for operating the brake.  Just because this system is very simple, it does not mean there is not a lot to figure out if you want it to function well, and the fact that all stock systems are so very identical is worth considering.  There is in fact very little deviation possible without real consequences, which is why cable or hydraulic systems are often the "go to" solution despite their increased complexity and expense.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 15, 2019, 15:39:18
Thanks for the input mobius.  You managed to explain what I have discovered/realized with this linkage during this process.  A mechanical linkage, no matter how 'optimal' will always be 'sub-optimal' in this particular application.  And I agree, a cable set up would be much better.  I think I'll weld a cable holder to the swingarm before powder coating it - just in case I need to redesign the rear set linkage and go down this route - I will try the mechanical linkage first.  Besides, as you mention 'On a street bike it might only be an annoyance,  but it would be intolerable on a road race bike' - absolutely true.  A road racer would be using the rear brake a lot more eloquently than myself and would be annoyed by the weird feedback through the foot peg from the swingarm action.  But I don't (hope) think I will notice it too much.  Having the backup plan for a cable system already welded on place will give me piece of mind.

Check out the attached images for comparison of stock position for the brake link rod and the new position plus a forward moved suggestion position  - which with the brake arm lever flipped upside down, would be a similar/comparable position to stock. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 15, 2019, 15:43:04
Maybe I need need to weld on a 'cable stop' as they are called.  Looks like there is a bunch of either bolt on (drill and tap holes) or clamp on solutions available...
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 15, 2019, 15:48:53
On a very different note, I got a couple of update messages from Chris this week.  He said the exhaust thread detail in the head was too risky to weld up - too much heat distorting the head and too thin aluminium there.  So instead he turned up an insert and threaded that in place (and added epoxy) then re-tapped that.  It looks good! 

Plus he has installed custom bronze valve guides and turned up the custom Ti valves  8) 8) 8)

So happy there are pros that do this kind of specialised stuff, it is way out of my league. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: lunacy on Jun 16, 2019, 23:31:40
Iím watching this build with interest. I built an SR250 cafe racer (which Rex Havoc finished off) and always wanted to do more to the engine. I just didnít have the resources at the time.

Great methodical work!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 17, 2019, 08:10:41
Iím watching this build with interest. I built an SR250 cafe racer (which Rex Havoc finished off) and always wanted to do more to the engine. I just didnít have the resources at the time.

Great methodical work!

Whoa, things really have come full circle!  One of the main reasons I ever got interested in and started working on SR250's was because of your build thread back in 2008!  So I have a lot to thank you for sir.  And now you're commenting on my build thread, priceless. 

I remember being almost heartbroken when you declared that you wouldn't be able to finish the bike yourself and that you had to sell it on.  It was cool to see it get finished and featured on Pipeburn though.

Yes, I am doing quite a few interesting engine mods for this build so I am really curious to see how it all pans out  :D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 18, 2019, 15:34:31
And while I've got you here...  I notice on your bike you had a similar brake linkage set up!  I guess the bike was long out of your hands by the time it was being ridden and therefore cannot comment on its action/feel/performance?  The brake specifically I mean.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: crazypj on Jun 19, 2019, 00:09:36
Personally I've never been a fan of reversing the operating lever like that or having rod pivot point too far from swing arm pivot. Always found it made brake 'grabby' (putting main pressure on leading shoe instead of trailing shoe)  and the suspension operation was very noticeable
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 19, 2019, 12:16:43
Yeah that is a good point crazy, the leading shoe being pushed more than the trailing.  I'll make sure I have the cable back up ready. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jun 19, 2019, 12:25:12
I got these back from the machinist this week too.  They look great and I sure hope they fit!  To avoid needing the stock end seals (which go for 35Euro  each!) I increased their flange thickness a little (so they mate up to the inside of the frame) and added an oring groove on the inside.  This is to keep grease in and dirt and water out.  This works really well with other products I work on (water treatment industry) so hoping it works here too.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: lunacy on Jun 22, 2019, 01:11:56
Iím so humbled by your comments about my old bike. I was surprised at how much interest it received at the time, and there seems to be a lot more SR250ís being modified now.

Youíre right I never got to test the rear brake but Iím told it worked okay. I am very much a ďcardboard aided designĒ (TM) engineer and hand made all the customised parts on that bike with hand tools, electric drill, grinder, bench vice .. MIG welder, heat and a hammer. When it came to the rearsets and linkages I consulted my friend (an actual engineer) to check I had the basic ideas right, and looked at lots of photos of old racing bikes. If Iím honest I was quite pleased when it all worked  :)


Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jul 02, 2019, 07:49:13
Iím so humbled by your comments about my old bike. I was surprised at how much interest it received at the time, and there seems to be a lot more SR250ís being modified now.

True, I think around that time was the beginning of a boom of interest in the SR250.  It was somewhat of a natural progression from the SR400/500 though as they became harder to find and more expensive.  Either way, I think your build was highly influential to many DIYers   :D
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jul 02, 2019, 07:52:27
An update will be coming soon, but I have been working on a couple of other projects recently.  One is my daily rider - see images below.  It is getting closer and closer to something I really like and it is super fun to ride.  Pretty tricked out now too with all these prototype parts on it!  The fork adjusters are awesome!

The other project I have kept pretty quite about but to drop a hint, it involves a turbo.  Not a turbocharged vehicle, but the turbo itself (so others can turbo charge motorcycles easier). 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jul 07, 2019, 11:14:55
More work on the weight reduction program.  This is turned into more of an obsession rather than something that is going to effect the performance of the bike.  These kind of weight reductions will be inconsequential.  However my thoughts have been that if I can reduce part weight by 100g on 10 parts, thats a kg!  Haha. 

I really like how the top triple clamp came out.  There is probably about 5hours of work in that all up.  I used a hacksaw, auto file, dremel with sanding wheels and then sandpaper.  I removed a few big clumps of aluminium that were no longer needed and removed all casting marks and split lines.  I did not remove any material that I felt contributed to its structural integrity.  I will bead blast it to - to try and get a nice even finish. 
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: teazer on Jul 07, 2019, 20:18:24
That all adds up.  Does that bike have an aluminum steering stem or steel?  There's almost a kilo right there.

Then add hollow axles, aluminum wheel and bearing spacers, aluminum and Titanium hardware and your wallet will be lighter than the bike. It's addictive.

I wouldn't put Ti axles on a street bike, but Ti nuts and washers, for sure.  And alloy sprocket nuts and shock nuts.  Keep adding lightness until wallet is empty.  Replenish wallet and repeat.
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: der_nanno on Jul 08, 2019, 10:09:21
A hole is a poor man's titanium

 8)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: crazypj on Jul 08, 2019, 15:12:39
shocks I made some alloy lock-nuts. 4 alloy nuts were lighter than one original steel nut. Also made bearing spacers and wheel spacers from 6061 to shed a few more pounds. I bought some 7075 to make  new steering stem as it's fair bit stronger than 6061 but lathe is too small to be able to machine it. It willget used for something though (eventually  ;D )
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: zap2504 on Jul 08, 2019, 15:31:45
Interested in performance/operation comparison of front disk on "daily rider" vs front drum brake. I assume its from a Virago (or maybe just a newer SR250 that did not come to the USA)?
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jul 14, 2019, 12:42:33
shocks I made some alloy lock-nuts. 4 alloy nuts were lighter than one original steel nut. Also made bearing spacers and wheel spacers from 6061 to shed a few more pounds. I bought some 7075 to make  new steering stem as it's fair bit stronger than 6061 but lathe is too small to be able to machine it. It will get used for something though (eventually  ;D )

Great tips!  Imma open up these wheels and make aluminium spacers :)
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jul 15, 2019, 06:21:55
A hole is a poor man's titanium

 8)

Haha so true!
Title: Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
Post by: JadusMotorcycleParts on Jul 15, 2019, 06:26:40
Interested in performance/operation comparison of front disk on "daily rider" vs front drum brake. I assume its from a Virago (or maybe just a newer SR250 that did not come to the USA)?

The front end is standard on the later model SR's - which were only manufactured in the Spanish Yamaha factory.  This fork and disc brake is on models from '95 onward.

I find the disc marginally better than a well dialed in drum.  That is because I hardly ride hard enough on twisty enough roads to experience fade, which is where the disc would out perform the drum.  Bite is of coarse a little better with the disc as well.  The lackluster performance is also because it is a single pot set up.  This could probably be improved a lot with better pads, a better disc or upgrade to a twin pot set up.