125 Top end on 100cc engine?

[badlydamaged]

Hey there,

I have a 1988 Kawasaki kH100 and have the oppotunity to purchase a KH125 Top end (piston, Barrel, Cylinder head etc). I was wondering could I swap the 100cc top end with the 125 one while still using the same carburettor, exhaust and bottom end? To me it seems possible, knowing that my friends RG has has a TS125 top end on (giving it 150cc).

From imformation I have found on the KH125 and KH100 engines the later 125cc engines(which is the engine type I am looking into) have the same stroke (and presumably the same crank shaft) as my KH100, so maybe my engine could be adapted to take the 125 top end and Piston?

Both 125cc and 100cc engines use the same side carburettors, are rotary disc valve strokers (with the same ignition timing) and both bikes use the same frame and have the same gearbox. The only thing I am concerned about is that the top end stud spacings may be different, meaning I couldn't bolt down the barrel onto the crankcase assembly, but obviously this would be impossible to tell until I started trying to fit it.

So does anyone think this is possible, or are the two engines likelly to be different in small ways so the top end isn't interchangable? It would interest me to find out .

Hope someone can help.

Cheers, Jonathan
____________________
My bike: 1988 Kawasaki KH100 Status: Polluting Devon with two stroke smog and noise pollution!
"Its not your engine size that matters!, It's what you do with it that counts"
Add me to MSN if you want! badlydamaged@hotmail.com.

[Robby]

The KH is a twin, no?

I reckon the 125 top end should fit, seeing as the 100 is probably a sleeved version - or 125 is bored, either way, should be the same stud spacings. You'll need 125 gaskets.

Assuming the rods run the same size small end bearings, you should be able to pop on the 125 pistons with new gudgeon pins and clips and bolt the barrel and head on.

I would expect you can use the same exhausts and carbs, but probably up the jetting about 15%.

Give it a go and see. Should be an interesting project.

[badlydamaged]

Hey there, thanks for your comments

The Kh is a single, the 100cc was launched about 10 years before the 125 (although they both continued into the 90s) so I wouldn't think it is sleaved down unfortunatly, which was why I was wondering about the stud spacings, but like you say I think they could be the same.

However the whole bottom end seems identicle on both engines from the specs, even down to using the same clutch! But in pratice I wouldn't be suprised if there was some obscure and odd difference between the two.

I have actually got a slightly bigger carburettor off a GP125 waiting to go on the existing engine, the GP series and KH Series (including the tripples oddly enough) all used the same carbuerttor types as far as I can remember, just different bore sizes. I think I should be alright with a main jet size of 95 (original KH125 main jet size), as im not intending on doing anything stupid with the engine's state of tune.

Like you say, it should make an interesting project, and these parts are going to be cheap, so its worth a go!

Thanks again, Jonathan
____________________
My bike: 1988 Kawasaki KH100 Status: Polluting Devon with two stroke smog and noise pollution!
"Its not your engine size that matters!, It's what you do with it that counts"
Add me to MSN if you want! badlydamaged@hotmail.com.

[badlydamaged]

Hey again, for anyone interested I have just spoken to my mechanic and he says that with these engines the 125cc top will go straight on without problems, he says the same is true of Suzuki's GP100 / 125 . If anyone is interested I will let you know if there are any probems when I get round to fitting .

Cheers, Jonathan
____________________
My bike: 1988 Kawasaki KH100 Status: Polluting Devon with two stroke smog and noise pollution!
"Its not your engine size that matters!, It's what you do with it that counts"
Add me to MSN if you want! badlydamaged@hotmail.com.