I have a 2001 YZ250 that has been trashed. Out at the new MX track last Sunday when I heard an awful noise. I sounded like a push mower running over a rock and the rock comes out in little pieces. I was in upper revs statring to shift when it happened.
Of course the bike died immediately. After I removed the head, I could see a small piece of debris setting on the piston. I reached down to pick it up and the entire piston head fell down to the bottom of the cylinder. After I removed the piston head, I could see that the entire skirt on the piston had exploded.
The cylinder has some nicks in it so I know what is going to happen there. But what I'm confused about is how this happened.
From what I have read is when this type of failure occures, it's usually due to "The skirts of this piston shattered because the piston to cylinder clearance was too great. When the piston is allowed to rattle in the cylinder bore, it develops stress cracks and eventually shatters." According to the Eric Gorr web site.
The piston, rod, cylinder, berrings, gaskets, etc are all stock. This doesn't jive with that. Does anyone have any idea how else this could have happened, because I'm at a loss. Overheated? Fatigue? Lack of oil?
Some facts: Top end is no more the 15 hours old. Bel Ray MC1 at 40:1 with 93 Oct. Filter was fresh that morning. New plug NGK BR8EV. About 4 hours on the case oil. If there are any other facts you need to know, please let me know.
Thanks for any input anyone can offer.
Of course the bike died immediately. After I removed the head, I could see a small piece of debris setting on the piston. I reached down to pick it up and the entire piston head fell down to the bottom of the cylinder. After I removed the piston head, I could see that the entire skirt on the piston had exploded.
The cylinder has some nicks in it so I know what is going to happen there. But what I'm confused about is how this happened.
From what I have read is when this type of failure occures, it's usually due to "The skirts of this piston shattered because the piston to cylinder clearance was too great. When the piston is allowed to rattle in the cylinder bore, it develops stress cracks and eventually shatters." According to the Eric Gorr web site.
The piston, rod, cylinder, berrings, gaskets, etc are all stock. This doesn't jive with that. Does anyone have any idea how else this could have happened, because I'm at a loss. Overheated? Fatigue? Lack of oil?
Some facts: Top end is no more the 15 hours old. Bel Ray MC1 at 40:1 with 93 Oct. Filter was fresh that morning. New plug NGK BR8EV. About 4 hours on the case oil. If there are any other facts you need to know, please let me know.
Thanks for any input anyone can offer.