Thanks very much for your help. I wasn't going to strip the motor but when I removed the barrel to upgrade to the big bore kit, I found broken rings on number one and four pistons as well as a gudgeon pin circlip missing on number one piston. I'd dropped one broken ring into the crankcase cavity and while retrieving it with a magnet, I also found other broken rings obviously from a previous issue, and a 10mm nut and washer chewed up that appeared to come from one of the retainer caps for a camshaft. The gudgeon pin had been rubbing /scoring the liner.
So, after inspection and flushing the engine which appears to have clocked up 87,000 kms, I decided its probably best to strip and carryout a proper inspection and replace the chains while I am doing that.
I am rebuilding the bike so this seems the correct action to take.
My issue though is the culprit is supposedly a reputably bike restorer. But reckoning is coming. Hopefully he will ask me how the project is going, in a room full of fellow bikers........
