Stovebolts have a nasty habit of wearing a dimple in the tips of the rocker arms where they contact the valve stems. That usually results in a noisy valve train because the true clearance can't be set with a feeler gauge, or a chewed-up feeler gauge if it's inserted between the rocker and the valve with the engine running. Some valve grinding machines have an accessory designed to reface rocker arms, but there's a lot of controversy about how accurate a radius can be done that way. In my decidedly biased opinion, a smooth rocker tip is better than one with a big hole in it regardless of how technically accurate it might be.
Jerry
