My buddy has an 87 scrambler 400. About 2 yrs ago we were riding and he blew the motor. Pieces of piston throughout.
Took him about 7 months between work, the family but we finally rebuilt it bored it and off we went. One and a half hours, blew the motor.
6 months go by, rebuilt it. 2 hrs blew the motor.
Just rebuilt it, he 's afraid to ride it. Puts around the yard its fine. Rev the motor in neutral and it sounds like a champ. putting around the yard, fine. Get on it and put the motor under load and the motor makes a sort of ping sound. Neutral, race the motor, Camp. Under load again ping sound.
We took the cylinder apart before he blows it again and it appears that half the sleeve is slightly higher or above the cylinder.
Any suggestions?
Besides buy a new machine.
Let me throw in a few more details,
Mods:
FMF exhaust, Carb bored by dynojet 1 over, Weisko piston bored 20 over,
Boysen reeds, EPI sport clutch kit, oil injector removed and runs 92 oct @ 40:1
Changed from B8es to B9 to run cooler Due to a hole melting through the top
of the piston.
The ping is probably best described as a high rev. knock. machine also seems to be overheating (in the cold snow conditions too)
Thanks again and hope someone can help.