As always, clicking on the blue arrow icon within any quote box will take you to the original post/thread.Greg
The camshafts run directly in the head with very small clearances, if the head is warped when you take it of it means it had stress in the casting caused by being driven when it was to hot. When the head is bolted to the block it is held straight by the block and the cams are able to rotate, when you take it of, the head bends due to the stress and the cams will lock up. If you then machine the head in the bent shape the cams are still locked, so the repairer may bore out the cam bearings to allow them to spin, this destroys the head because the cam shaft is no longer in the correct location to open the valves and allow them to close again. As others have said the head or any other overhead cam head are not machineable. Eric.