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jahern059

06 YZ 450F Noise

7 posts in this topic

Heres the rundown. I bought a 06 YZ450 with a good amount of begginer time on the track and once (i was told) at the dunes. While at the dunes had a pretty good crash that bent the r/h side of the subfram. Shocks were blown and the bike started but backfired like no other. Keep in mind i did buy this bike for dirtcheap!!! So after looking into it, the cam chain had jumped a tooth from it being so stretched and the tensioner was shot. The clutch was toasted and the oil had never been changed from when it left the factory floor as well(felt and looked like grease with a whole lot of aluminum in it). After spending a decent amount of money, the bike starts and runs like a champ but still has the very loud knock????? Im a bit worried to take it out riding fearing its going to detonate on me, any ideas????? Im a desert rider and really dont like being stuck in the middle of nowere. Any help would be great, Thanks

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So...I assume you didn't have the top end off? From your description of the condition of the bike when you bought it, it sounds like you may have a bad crank or a very worn out piston. The only way of knowing is to tear it apart and inspect. If the noise is that bad you definately don't want to ride it untill uou have found the source of the noise. Any riding in that that condition and you may end up with a broken piston or rod.

Edited by 2grimjim

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Heres the update. Tore it down and the cylinder is warped with the piston cocked at an angle that its lightly tapping the cylinder head, but no major gouging. I feel like a fool but again, picked it up for real cheap. Thinking of just moving forward and buying what I need and ill pretty much have a somewhat new bike.

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The cylinder is not the cause. There's either a piston or ring problem allowing/encouraging an excessive rocking of the piston at TDC, or you have a dangerously loose big end bearing.

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