well I put a 90 KX125 Piston in my bike. The issue you have w/ that is the fact u have to figure out a way to get the connecting rod to work w/ wristpin. Let me tell u if u just blew ur topend (hole through piston :) ) just buy the orginal parts to fix I dicked and messed w/ my 125 so long it wasn´t worth it and I just ended up scapin the motor later anyway. If ur gunna try a swap like that make sure u get the parts for virtually nothing because it would suck to spend all the money like i did and then end up w/ junk. Just buy the 175 motor and swap.