I've sent my heads out for some porting and flow work. I noticed a couple seat/valves on the exhaust were not completely closed, and rotating the valve did not change the opening. My guess is the seat had moved, I asked the head guy about this, and he said it's common in Aluminum heads. Whats the cause of the movement? heads running hot? engine running too cold? I asked a buddy, for what heads gasket to use, he said he used Cometic, but open the steam holes on the exhaust side to the size of the passage. His guy suggested the seats got hot, any suggestions? Thanks in advance...