2007 Kawasaki kx250f piston and cylinder problem

So I bought a 2007 kx250f and it needed a new piston and rings along with gaskets and valve shimming. I redid the valves and shimmed everything correctly and put on new gaskets. I also redid the piston and rings and put it all back together and it ran for a total of 5 hours then something happened with the piston and the cylinder. It had low compression so I tore it down again and saw this. I am not sure what could have caused it so that is why I am here asking. I think it might have something to do with the oil jet. The scrape is on the opposite side of the oil jet and the same thing happened to the first piston that I removed, but this one was about half an inch over still on the opposite side of the jet. I also read that it might be because the piston may be outta round, although it looked fine when I put the piston in the beginning. I am open to any ideas of what it might be because I am not sure.5a04bbc2eb502_20171108_1047481.thumb.jpg.51fe872539f0f13fbce69033bc8189ba.jpg5a04bafa2f212_20171108_1225091.thumb.jpg.02687e7b37a155c6cab84199340187c8.jpg

I see this as typical damage from incorrectly installed oil rings set.  It is very easy to get those messed up and overlapping improperly.  Also, when the oil rings are put in, the ring end gaps need to be angled away from each other.   Proper oil ring end gap locations are shown in the service manual.


Edited by FaceDeAce

There's hundreds of threads on here about 10 year old bikes being rebuilt that don't run too long after the rebuild.

Seeing the first damaged piston (not normal wear) should have been an obvious visual indicator that

something else needed attention rather than simply replacing parts.


If you can grab any scratches in the cylinder with a fingernail it also needs to be replaced.

(looks to be one at the very bottom)

Edited by mlatour

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