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Yamaha MX & Off-Road Dirt Bikes
How bad must you melt a piston before it has to be replaced?
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[QUOTE="ws6transam, post: 1419122, member: 65064"] I finally got the piston out today. It was galled up on both sides nearest the wrist pin hole, and there's light scoring on the cylinder wall. The piston got hot enough that the wrist pin discolored with the slightest sign of brinnelling on the needle bearing race. The underside of the dome has baked-on oil, and it's brown all the way up to the wristpin and the back side of the exhaust skirt. It must've gotten really, really hot! Everything else looks great. There's lots of extra oil still in the bottom of the crank case.The lower ring is stuck in the groove and won't move anymore. As for the top, only the one edge that faces the exhaust port, about 1 cm, had visible signs of melting. All in all, minor damage but yeah, the piston's toast. It would've just gotten worse with time and wrecked something else eventually. There was three summers, and 60-some hours of run time on the top-end anyway. I'm not sure if the cylinder will clean up with honing or not. I'll probably put it in a box and send it off to Eric Gorr, since he did the porting for me last time, and let him determine what it needs, and let him pick up the appropriate replacement piston. [edit] Looks like Eric is out of the office for all of September. Anyone else have a suggestion as to where I should send my piston and cylinder? [/QUOTE]
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Yamaha MX & Off-Road Dirt Bikes
How bad must you melt a piston before it has to be replaced?
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