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: Ryan Stecken 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  = .0032 @ 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?  .0032 = .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  = .0032 @ 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?  .0032 = .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

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 Ill 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 aint running at the moment.

Just send me a drawing and your address and Ill 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 Ill 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 Caf 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: The 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  :)