I sent my 250x to anvanced maching and got a big bore kit, proformance cam and valves and i got it ported and polished also a wiesco piston. i have got it back a week ago and put it all together and it was great no problems i rode it for about 2 hours and then took it home this week end i started it and rode it a lap around the yard and then let it idle for w few minutes and it started clanging really hard in the moter so i shut it off and started it again and the same thing happened but it only calangs when i rev it up a little so i took it apart and realised that the piston was hitting the valves so i checked the timing and it was a little off so i set it where it needed to be and put it back together and started it and the sound was A LOT WORSE!! so after i done a valve agustment to make sure it didn't need it but they were fine and i checked the piston and its fine no bad rings or nothing and my valves are not bent so i put it back together and it still had the same problem so i put my old cam in the engine thinking that the maching place gave me the wrong one and then we put it back together and did what we were supposed to do and now the STUPID thing wont even iddle without the piston hitting the valves anything will help

THANKs
FMF MegaMax
uni filter
big bore
proformance cam and valves
ported and polished
MIKUNI carb

 

A..........how do you know the piston is hitting the valves? Valves bend VERY easy. They can't stand much of a side load on the head. Did you check the valve to piston clearance when you put it together? When the valve timming is on the money your need about .080 clearance. Your going to have to check everything before you put it together. Who knows what is bent or broken now. Unless you put together a known combination, you have to check everything.