Thanks for the replies folks. I think I've found the problem.
The locking wire on the 3 bolts behind the engine sprocket had snapped, allowing the wire to abrade against the sprocket. There's no damage to the sprocket or chain that I can see. I suppose the soft wire could be pinched by the sprocket & chain, snapping off small pieces. I'm surprised I didn't notice this when I replaced the chain.
As for the plate behind the clutch that Allan mentions, I don't really understand this. Mine looks in good nick compared with others, it mounts loosely on the inner chaincase with horizontal & vertical movement. I figure the circular opening must contact the rotating clutch to some extent. Does it rely on oil being flung about for lubrication?
My footrest spacer has a few gouges, a chain must've let go a long time ago.
I'm relieved you've found the source of the metal filings. That safety wire is important, so you've just saved yourself from future problems, if the bolts come loose.
As for the plate behind the clutch, my understanding is that it is moveable so that it centers on the gearbox shaft. Once centered it needs to be tightened firmly in place. if it's loose it will start to rub on the shaft and worse.
Ditto...The plate should be able to slide back and forth relatively freely..As the hole in the plate is circular and the back of the clutch sleeve is circular there will only be a 'point contact' anyway and if the plate is free to move there won't be any contact pressure on it either ...Ian
