Motorcycle Repair: Engine damage, piston crown, piston kit

Question
I have an 2006 rm250 the bike runs great owned it for less than a week. I rode it twice on a supercross track. The second time I rode it I came off a 40 foot double and it started hammering. Right away I shut it off hauled the bike home and tore into it. Something got on top of the piston causing this noise. The cylinder was just re sleeved including new piston kit. I checked every piece in the power valve and the crank seemed still pretty tight with only a hair for vertical movement. I have no idea what caused this engine failure. I had the cylinder checked and it seemed to surive the failure. I'm wondering what could have caused this and if I should put a new piston in it and just run it.

Answer
Zach, if the piston is out of round or the ring lands are damaged, then a new piston is in order. You have to determine what the nature of the foreign object was and be assured that it doesn't happen again. Shake out the exhaust pipe and see if you can determine what went through the engine. The damage to the piston crown and cylinder head squish band might give some clues as to the shape of whatever it was and then where it came from.

It could have been a leftover bit down in the crankcases from the previous overhaul that wasn't found or it might be from the crankshaft, itself. You were lucky not to have destroyed the cylinder bore with something like that flying around inside the engine. Take a close look at the air box/filter, connecting tube, carburetor bore/slide, intake/reed valves, and on through the whole engine from air inlet to the end of the exhaust system. Pressure waves can pull objects back into the crankcase from the exhaust system in extreme cases.

Bill Silver