Like an idiot I managed to drop the bike while on loose chipping, got it upright tried to restart and after a bit of a rattle the engine stopped dead. Anyway after a complete tear down I found a nut jammed in the primary chain - looks like a cylinder head nut to me and although I have had the head off in the past I know I have not dropped a nut so I can only assume that the nut was stuck somewhere in the lower crankcase for years and was only disturbed when the bike tipped over - all very strange but the good news is that it is all up and running with new primary chain, oil seals, cam chain etc, not a job I expected to be doing though.
