If someone changed the valves there could be a few different problems. 1- what length valves did they use. 2- what springs and retainers. 3- were the correct length push rods used 4- what camshaft and lifters were used 5 - were the heads and or block milled Torquing down nuts on factory bottle neck studs only works when the factory valves are set up to factory valve heights using the factory camshaft, lifters,push rods.
