Guys i need some help. My bike was starting to have a slight knock in the mid range and would get worse as it warmed up. It wouldn't knock at idle or at full throttle. The knock started getting worse so i took it apart and the piston had a crack in it and was pretty scratched up. Got a new top end installed and all put together and started it up and warmed it up and headed out for a test run and it did the exact same thing only this time i would consider it worse. All the bearings are tight tho and no rod movement. could it be piston slap? it has plenty of comp (180psi) but this one has me stumped. Any ideas? Thanks

what is your jetting, maybe not enough lubrication?

what was the piston to wall clearance? forged or cast

90% the reason your piston was cracked was it was ran loose in the bore too long

Well whats strange tho is the new piston is starting to have the exact identical marks on it. And it has less than 10 minutes on it! I feel that the jetting is correct. i read that i should put some octane booster in the gas and that should clear up the knock but i dont believe it. Could that be true tho?

If i get the cylinder bored and re-sleeved to standard bore would it fix the problem?

Bottom End. My 04 Rm250 had the same issue.

Crank and bearings are out of spec.

Just noticed your in MS. I live on the coast.

I have all the tools to do a bottom end and the experience with this bike. Send me a Private message if your close enough and would like it done for you. Would save a good bit over dealer cost. If not it wouldn't be a problem to help you with the stages on here.

just as a follow up, the cylinder is being sent off to Racers toy store to get resleeved and inspection of the power valve.

Think this will help? This will need to be done anyways so wy not try it first and see what happens. thats just the way i see it

It sounds like the bottom end needs a rebulid probably a rod kit and crank barrings would fix it