Bit of an update on my Ipotesi. Like riding it regularly and also giving it the berries on occasion. I was therefore concerned with the reports of valve seat failure on this and other forums. I therefore took Adrian's advice and removed the head and had it assessed. The engineer who did the work was surprised with the average quality of the head casting and the poor valve seats (in terms of seat material and depth of fit);. He said it was a recipe for disaster and therefore needed replacement. He did both inlet and exhaust seats. The pics attached tells the story. One pic shows the job done another has the old seats shown after removal. He said that the seats appeared to be made of material little better than mild steel and were very shallow in the casting. The seats were easily bent which does not indicate hardening to any extent. The moral is to replace your seats before disaster strikes. The last pic is of my top end just before I replaced the tappet cover this afternoon. Result was a first kick start, and a quick ride. The job included fitting quality and thicker seats, decking the head gasket surface and refacing the valves. The valves were of very good quality and little wear was evident.