Last Saturday at the track my friends 250sx refused to restart after an tip over crash. He has had problems before with wet fouling the plug after a stall. We turned off the gas and kicked to try and dry off the plug. When it finally restarted the bike made a god awful racket that I thought sounded like piston slap. I quickly hit the kill switch and let the engine die. I kicked again and the bike had lost all compression. After about two kicks it seized. I put it in gear and rocked it which broke the piston free. Pulling off the filter showed that some dirt had gotten by. At this point I assumed that he had prematurely worn the piston. Breaking down the bike however I discovered this.
I'm pretty sure that a little bit of wayward dirt did not cause this kind of damage it sure looks like something broke off inside.
However I'm at a loss as to what is broken?
The sparkplug was whole and in good shape.
Both circlips were still intact.
The needle bearing holding on the piston was intact.
The ring was damaged from the object but was still in place.
I have read that the connecting rod needle bearing can cause this problem? However the crank still spins freely and does not appear to have an excessive amount of slop. Is there way to check that bearing without splitting the cases?
Also when looking at the crank the oil residue on it was black like motor oil, and not red like I'm used to when running Amsoil. Reading on here this could be the right hand side crank seal leaking oil. I'm wondering if it is possible that if we had oil transfer over maybe some shavings from the tranny worked into the crank?