so, my oldest kid,15, rebuilt the top-end on his kdx 200, after getting it back together and running it for about 2 hours it losses compression and locks up. after tearing it down again we see the bottom of the sleeve is trashed. i told him there might be a chance that the wrong rings were used. the new sleeve he had put in is steel, im not sure about the rings, other then they were new...

any other ideas?

we will be putting a new piston in it after the cylinder is bored.

thanx HB

 

the stock rings were meant to be used on nikasil, not steel. But I doubt they would rebel that much. Most probably the main jet is too lean or the crank seals are leaking or the head gasket is leaking.