Kawi2strokes.com Forum

Hello Triple Brethren...

Like the title says, I have some questions about installing S3 pistons on my S1. Why? For the righteous pursuit of speed, horsepower, and fun (and not being able to leave well enough alone )! Now, after reading up on the "old board", I've learned that I would have to have the upper crankcase cylinder holes enlarged. That makes sense: larger diameter=larger hole. Although if i went with S2 cylinders, it would be a direct swap. No larger holes required. But why settle on a 350 when I can have a 400? Less "headaches" maybe?

Here's my first question...could I swap out my engine internals and fit them into an S3 crankcase? Do all the S series bikes share the same lower engine (crank, connecting rods, trans, etc.)? I'm also assuming the cylinder studs are the same (spacing, length)?
My second question is...Would the S3 cylinders have to be modified in any way? I seem to recall something about modifying the skirts?
Third question...Can my S1 heads be transformed (machined) into S3 heads? I want to get them machined to the proper squish angle, so I was thinking that instead of buying some used S3 heads and having them machined, I'd save a few bucks and have my S1 heads modified. No? Undo-able? Not worth the trouble or cost? What the hell is this guy thinking?

Well, that's all the questions I have. I'm just in the "what if" stage right now so I'd appreciate any info, either to steer me in the right direction or convince me not to do it! Thanks.
Dan

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Chong

You probably know, but the S3 cylinders fit the H1/H2 sized head pipes, and are not interchangeable with the S1/S2 exhausts.

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If it surges, that's normal, upshift.

You are in for a few buckets of money, just find a 400 motor and drop it in.

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

It can be done, one of the guys on RB's old board did it. But what a lot of trouble to go through when you could just swap a whole motor. Stud spacing is different too.Crank and gearbox are the same, but the 400 clutch and oilpump are different (probably a few other things too) externally the pipes and carbs are different.

A 350 topend is a much much easier idea, it all just bolts on.Ive done that in the past.
A 400 conversion is easy if you have all the bits. I did that to a KH250.
Walms 500 conversion looks like a good thing (The current top photo).
It's your bike, do what you want, all the above will transform an S1

that I can say is, according to Leo, you can fit S3 Std bore piston on a S2 barrel but the sleeve would be very thin after

I didn't know about the oil pump and clutch being different. Thanks for the info. You're right Ja-Moo, if I wanted to change my engine to a 400, buying a complete engine would probably be the best idea. Swapping out engine internals is tempting because I see on Ebay s3 or kh400 engine cases going for around 50 to 80 bucks. But I can see there would probably be unforeseen headaches down the road putting everything together. Would the 400 engine mount to an S1 frame, without any mods?

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Chong

I bvelieve they all have the same engine mount locations.....

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

Yes all S series do. 400 into 250 no worries, an S3 would be better than a KH400 (same ignition etc). Only question may be rear exhaust mounts, if it's an early (72) S1 as you are in the US that's unlikely.
Anyway I'd investigate Jim's Denco replicas rather than the stock pipes.

There is almost no power difference between a stock 350 and a 400...so why not stick with the 350 top end? The other "upside" of the 350 conversion is that it still looks like your S1 motor, so you can fly under the radar (if you want to). The 400 can be identified as such from 50 yards away. Also, 350 Wossner pistons are already available and the 400 pistons are not (as far as I know).

I like your thinking on this!