Bevel drive nasty!
Posted: Tue Oct 31, 2023 12:26 am
Quick background story before I get down to the nitty gritty. I bought a beautiful immaculate 350 Mk3 from a bike dealer a few months ago. It seems to be a bitza, being an Italian head with a Spanish bottom end. All seemed OK until I checked some chassis nuts and bolts and found many to be barely tight, as were the cylinder head bolts, I also realised the completely clean engine oil (as delivered) was extremely underfilled, by 1 litre or so.....
So I've run the bike while the summer weather lasted, for about 300 miles, sorting out the over-rich carburation as I went.
Now that wet autumn weather is here, I drained the oil and removed the timing side cover to check that the Spanish plastic idler gear had been replaced with an Italian steel one.... which it has..... HOWEVER, I found a whole load of nastiness on the lower bevel drive, detailed photos below.
Although there were a few fine metal filings on the outside of the oil strainer I dredged a strong magnet through the old oil and nothing metallic attached itself, so either the damage happened prior to me obtaining the bike or there are bits of bevel metal still inside...... The engine is very clean inside and out so I suspect it hasn't been run very much since someone, somewhere, worked on it.
So, can people suggest what might have triggered this damage? I see that the lower bevel pinion should be shimmed, has that been badly done, or some other cause?
As for fixing the problem, it looks like the crankcases have to be split to release and replace the pinion, I haven't stripped an engine down like that for many years and don't really want to do that now.... could I get away with replacing just the crankshaft pinion (or will the problem just reoccur)? The bevel pinion appears worn, but possibly not too damaged? I'll probably run some flushing oil through to clear any residual debris, if that's OK on these engines?
Any comments gratefully received.
So I've run the bike while the summer weather lasted, for about 300 miles, sorting out the over-rich carburation as I went.
Now that wet autumn weather is here, I drained the oil and removed the timing side cover to check that the Spanish plastic idler gear had been replaced with an Italian steel one.... which it has..... HOWEVER, I found a whole load of nastiness on the lower bevel drive, detailed photos below.
Although there were a few fine metal filings on the outside of the oil strainer I dredged a strong magnet through the old oil and nothing metallic attached itself, so either the damage happened prior to me obtaining the bike or there are bits of bevel metal still inside...... The engine is very clean inside and out so I suspect it hasn't been run very much since someone, somewhere, worked on it.
So, can people suggest what might have triggered this damage? I see that the lower bevel pinion should be shimmed, has that been badly done, or some other cause?
As for fixing the problem, it looks like the crankcases have to be split to release and replace the pinion, I haven't stripped an engine down like that for many years and don't really want to do that now.... could I get away with replacing just the crankshaft pinion (or will the problem just reoccur)? The bevel pinion appears worn, but possibly not too damaged? I'll probably run some flushing oil through to clear any residual debris, if that's OK on these engines?
Any comments gratefully received.