2nd Dec 2015
we were on the road between sections on the Cotswold Trial, luckily just taking it relatively easily and there was a nasty crunching and grinding noise, so I switched off and coasted into the drive of a very posh house. I thought that the clutch had gone pop! Unfortunately not. So just do do a little more damage I started the engine again and the noise hadn't gone away - bugger! We gave up at that point. Got it home, pulled off the front cover on the crankcase and their was pieces of piston in the crankcase. Took off the left hand head and found a broken off valve and holed piston!
If anyone has any 85.5mm diameter pistons with a 50mm compression height....