440 problems ,new motor

Was it a new bolt or the original one? Sometimes you're better off with the original. I had a bolt come loose once on a Mushroom lifter cam. Went to a 3 bolt after that. You want a hi grade bolt, 6 or 8, torqued to 40 ft lbs and use loc tite. Mine bent 6 valves. Had to pull the heads and change some valves.