on my 250x do you think i would be ok heat wise with a .40 overbore, just wondering if thats safe being aircooled? and if i went up a tooth on the front sprocket, i wouldn't have to do anything special except loosen the chain some right?

 

it will be fine with .40 over. heck my buddy is running a 78mm big bore in his with no problems. as far as the chain im not sure, you prob will be ok running the standard length chain.

 

All you have to do is adjust the chain to make up for the sprocket. But im sure your engine would heat up sitting still but as far as riding i would say you would be ok.

 

Have you trashed the cylinder? I would think it would tolerate 30 or 40 over, but that increase is so slight there's really no reason to do it, unless it is to reuse a stock cylinder that is scored or worn beyond service limits.

 

yea it's probably gonna need a top end rebuild,havn't tore into it yet though $$

 

If you don't have the appropriate micrometers, take the cylinder to a machine shop to get it measured. It might be within limits and only need a pass with a hone, or maybe needs bored to 10 over, which would let you rebore again if needed in some future rebuild.