I have recently restored a non running 1986 ETZ 250. The engine was completely stripped as it was full of water when I drained the gearbox oil. I had the crankcases cylinder etc vapour blasted prior to rebuilding the engine.
All bearings and crankcase seals were replaced and I scrupulously cleaned and inspected all other parts before reassembly and rebuilt the engine very carefully using a Haynes manual. I didn’t strip the gearbox as I could not see any defects from a visual inspection.
I have started to run the engine in and all is fine until I select fifth gear. When fifth gear is selected there is what sounds like a metal on metal rubbing noise. I would be very grateful for any advice as to what the problem might be before I strip the engine again.