The last owner must have floated the valves, and the exhaust valves tapped the pistons. It must have happened early in the 3k miles that was put on the newly built motor, because carbon was already over the marks it made on the pistons. Any way, the bottom of the n42 was straight so i put new exhaust valves in the head. I went to put the cam back in, and it would not go through the last cam tower. Found out the top of head is warped. I have been contemplating shimming the tower because everything else is good.