Engine Report

All pushrods, rockers and valves seem to be in good order. There is no bent rods, cracked or broken rockers, springs or valve stems and nothing was loose. Pulled plugs and turned the engine by hand to check piston movement. All pistons are moving fine within each cylinder. They all have pressure, vacuum and no noise at top or bottom of the stroke. Since nothing was binding and I heard no noises, I cranked the engine electrically to watch valve and rod action while listening for noises I couldn't generate by hand. All valves were opening and closing, push rods were rotating in their seats, no excessive looseness or binding, and I heard no unusual noises inside or out. Everything seemed to be as it should be. A real puzzle to me, because the engine really produced a hammering sounded indicating that there was something VERY mechanically wrong just before shut down. Could the overheating cause the engine to produce a hammering sound like that? I have been thinking about how to accurately describe the sound, and it would be as if I were repeatedly hitting the side of the engine block with a large ball peen hammer. I'm planning another compression check to make sure the heads weren't damaged do to overheating. What next?