I have just removed the rods and pistons from my 65 f/b and found 2 top rings broken and five cracked pistons .. on the skirts ... one really bad one that goes up to the rings and you can see daylight through!! I was going to measure the bores for taper, but I assume that it will need reboring now, it is already +30 so it will have to be +40 or 60 next. What causes pistons to go that way .... overheating, lack of oil or just over-revving? Is it a common thing? It should be interesting getting the block rebored here in Spain as they don't do thou's, just metric ... so I may have to do an accurate measurement conversion