Just took the top end off of my rebuilt '71 R75 after 100 miles due to a ridiculously loud banging sound from the right side. Seemed almost like rod knock, but it wasn't. Turned out to be this...:eek1 Right Side: Left Side: Any ideas what can cause this? I used the original, .5 mm base gaskets/shims rather than the low test, 1.2mm shims. Could that have done it? It seems as if the valves only hit when they were seated, as it would have likely grenaded due to a bent valve otherwise. What should I do here? Any chance of the heads or pistons being salvageable? They are a fresh rebuild with under 100 miles on them. What should I do to make sure it doesn't happen again?