Crazy Rattling Top End

[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?

[kdxmaniac]

lower rod bearing? that would be my guess.

[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

[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.

[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?

[80elkster]

If your gonna split the cases dont forget to replace the crank seals.

[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.