The 1928 Flat Tank M18 started making weird noises on the way back home last saturday. Our first guess was that the bigend is gone. This sunday afternoon the engine was opened up to have a look. And everything looks pefectly fine; no vertical play on the bigend, no play on the main bearings.
So perhaps it's the gearbox after all. There seems to be more vertical play on the clutch than intended by the makers.