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.