I'm really interested on this thread. I have owned a 97 KX-125, a 2000 KX-250 and my boy has an 01 KX-125. I have never had a cylinder stud failure. However, when I recently disassembled the cylinder/head for a trip to Eric's shop on my boys 01, when I removed the power valve linkage cover, I was shocked, and amazed to find no nut on the stud at all. It was not floating around in the cover either, which leads me to believe that it was never present from the original assembly in Japan. The cylinder was being retained by 3 nuts! This bike has always run well, and was not babied, except for break-in.There was no evidence of blow-by, or leakage at the base either. I checked the parts list, and it indicates a nut should be there (I thought so too, but needed to confirm it), so when it goes back together, it will have one on it. Could these studs be breaking from frame flex torquing the head/cylinder at the headstays?
Smooth