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Bottom end failure sympyons

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I was at the track the other day with my 09 yz250f and after sitting for like 5 minutes after taking a break it was kinda hard to start but then I took off and this very loud noise occurred and my bike vibrated a ton. After I killed it my bike didn't start for a few hours then started and ran perfect but I don't really trust it right now, does this seem like a bottom end failure since my cam chain valves and piston are all brand new? And I suffered power loss when it make that weird noise.

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I was behind my friend the other day and he was riding his 07 YZ250F.  Same thing happened to him and I could hear the noise.  Then it seized!!  The bearing and crank shaft got fused together.  We still do not know the cause.

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Have you checked your oil filter?

+1 on this advice. When my 09 crank was going out i heard a small knocking while low rpm that went away as the R's rose. I checked my oil filter trackside and noted an unusually large amount of flecks in the filter. I cleaned the filter trackside and kept riding. I changed the oil and filter again before the next ride, put 1.5 hrs on the oil at moto speed and checked again. about 10X's the normal flecks (which is usually hardly any over a 15 hr interval) and realized I had something coming loose. Mine turned out to be the crank. yours may or may not be the crank.

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