It's all about the dirt..
- Nov 20, 2001
A friend of mine has an 03 YZ250F. He has raced the bike about 20 times this year, with about as much practice time on the bike as well. It has run flawless, and he has done all his regular maintenance. This past weekend the motor seized on him. He tore the motor down. The cylinder looked great except for a mark where the piston stopped. It's just enough to see, but yet not able really feel it or catch a finger nail on. The spark plug is typical brown, the valves are fine, and everything looks hunky doory. The one oddity that he did find was that the piston skirt had expanded and extra .001" in overall diameter. The lower skirt of the piston is .001" over what the service limit is supposed to be. It's not larger at the crown, but down at the bottom edge of the skirt. They put it back together and putzed around the yard for a few minutes and it seized again. Has anyone else ran into this type of situation? Looking for some insight as to why the piston would expand.