It's called "splash lubrication". As long as oil
comes through the pushrod and in the passages of the rocker shafts at all operating rpms, the valvetrain stays lubed. Lack of oil at the valvetrain causes wear on the rocker shafts, arms,
and valve guides. Big problems!! Most of it will start at the lifters, so keep the oil clean (changed on schedule) and use good quality oil and
filters.