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smooty

Crack in Piston??

9 posts in this topic

So here's my story.. My dad has an 03 450 and it has been since 2005 that i put a new pro-x piston inside of it, and it's probably got around 150 hours since then and last time we went riding it died and wouldn't get started again and so i did a leak down test and it was leakin air out the crankcase so i took it apart today and found that the piston had a hairline crack about the width of the piston about 80% across, the way that the pin is situated. My question is what causes this happen? I just have never seen it and am a little curious. thanks for the input!

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So here's my story.. My dad has an 03 450 and it has been since 2005 that i put a new pro-x piston inside of it, and it's probably got around 150 hours since then and last time we went riding it died and wouldn't get started again and so i did a leak down test and it was leakin air out the crankcase so i took it apart today and found that the piston had a hairline crack about the width of the piston about 80% across, the way that the pin is situated. My question is what causes this happen? I just have never seen it and am a little curious. thanks for the input!

Yeah I'm with YZFcranker.. I've never had a problem with OEM. But I've also run Wiseco and Athena with no problem.

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Pistons will crack along the wrist pin like this with high stress. I have seen this alot, with high hr motors and not doing oil changes enough on oem pistons. Like you said 150 hrs! since you put that piston in. Tops I would go would be 40 hrs, but I only ride mx.

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I figured it would be something to do with the high hours. the bike isn't pushed that much, more of a weekend rider just wherever we decide to go riding.. i probably let it go a little long though, oh well i'm just happy that the whole motor didn't explode and it'll only cost me less than 200 so i guess i lucked out!

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Aluminum anneals over time. The rate is directly proportional to the heat applied. Combustion temps are hot enough to easily anneal pistons over time. We see parts come back with 50 hours on them that have been annealed and are dead-soft (single digit Rockwell B scale). Pro racers can take the hardness down in 20-30 hours. The hardness is also representative to the strength of the material. Time+heat=reduction in strength. Change your piston sooner than 150 hours, and they will be far less likely to crack. Fresh pistons = cheap insurance.

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I can't really help, but Your daddy must be the luckiest fella alive! I mean one pull to the redline and that engine could have been completely gone, probably counter shaft could've been salvageable after breaking a piston.

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