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.