Crazy Rattling Top End

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jc7622
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Crazy Rattling Top End

Post by jc7622 »

My bike overheated in the last mud race, tore a radiator hose, lost coolant, blew a head gasket. I finished the race, maybe I should have quit. I washed it and started it after the race and it ran rough and had this terrible rattling noise when I raised the RPM's. Pictures of the piston, crank, etc are below. The cylinder looked fine so I lapped the head and top of the clylinder and re-built the top end. I started the bike up and hoped everything would be good. It runs much better and sounds smooth at idle but when I raise the RPM's it still has that bad rattling/vibrating sound. You can listen to how it sounds in the links below.





I looked high and low for something external that might be causing this. Anyone have any ideas? Could it possibly be the crank?

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kdxmaniac
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Post by kdxmaniac »

lower rod bearing? that would be my guess.
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Mr. Wibbens
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Post by Mr. Wibbens »

crank bearings


Did you spin it over a few times while holding on to the rod?


Should have been easy to feel and hear if it's crank bearings
Last edited by Mr. Wibbens on 05:05 pm Aug 15 2011, edited 1 time in total.
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gregp
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Post by gregp »

I would have the crank rebuilt (rod kit w/lower rod bearing and pin), and replace the crank bearings/seals while everything was apart. IMO, that is the only way to approach this job. You may as well pop in a new piston/rings while you are in there. Then, at least you will know where you are, engine-wise.
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gregp
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Post by gregp »

The discoloration on the rod is normal, and your piston has a little bit of blow-by, but again, it looks pretty normal (for a well used trail bike). It is very difficult (impossible) to identify these types of problems visually. Does the rod have *any* up and down movement at all?
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80elkster
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Post by 80elkster »

If your gonna split the cases dont forget to replace the crank seals.
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scheckaet
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Post by scheckaet »

that piston doesn't look bad, about the same amount of carbon deposit and blowby I had on my last top end.
It sounds really rough though, my vote would go toward crank bearing too.
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