How far out can you bore a piston/barrel? mm?

Question

My bike is an 84' Kx 80. The pistons and barrels have been bored out to 120cc becos of all the rebuilds. I didnt own it wen it had its last rebuild and it wont need another for a while but i want to know for the next rebuild could it be bored to 125cc?? Also how can it be 120cc if they dont make pistons that size?

p.s I have never opened it up to measure

cheers

Answer 1

I don't think you could bore an 80 out to 120cc, that would be huge.  I guess its possible that they put a stroker crank in there also, but that is still really hard to believe that they got that much cc.  Better open it up and double check whats there.  If there is not room for another bore you can always have it resleeved, or just pick up a used one somewhere like ebay.  I would say they could be had really cheap.

Answer 2

pistons aren't limited to 85, 100, 125, 250 (etc)

just because they don't make 120 dirt bikes, don't mean there isn't such a thing as a 120 piston (actually they go by MM but still my point stands)

everytime you bore it out you reduce it's overall life... you could technically bore it out to where there's only a 1/2'' of wall left... but it ain't gonna last long at all...