Crankshaft Problems

[jnnngs]

Hi,

Just finished stripping the engine on a bike that I finished earlier in the year.

The bike ran fine for about 100 miles, then started knocking at higher revs. Having stripped the engine turns out there is a lot of wear on the crankpin journal for cylinder #2. The shells have disintegrated and the crankpin itself has worn (now measures around 35.4, should be a touch under 36).

Every thing ese looks fine on the bike - no signs of wear on any of the other crankpins / main bearings.

What can cause this? Oil ways to that crankpin look OK, and I plastiguaged it when I rebuilt the engine and everything was in spec.

In the sump pan, there is a small amount of debris - looks like very small fragments of copper - is this just the disintegrated bearing shells? Not sure what else it could be?

Concidentally, I have another engine which has a similar problem. Bike had been standing for 25 years, and when I stripped the engine crankpin #6 was badly worn. Not got round to fixing this one yet!

Is worn crankpins a common problem - if so, caused by what?

Paul.