If the oiling system cannot fill a lifter fast enough, you would get "lift loss", or not enough lift inside the lifter to keep the push rod firmly seated in the lifter and rocker arm. This then would let the lash go to wide and cause rocker arm clatter. We used to call this valve float, since the whole valve train is in chaos.
If the lifter check ball sticks, then you could get full pump up or solid lifters and again the valve lash would go out of spec. only this time to little lash, thus holding the valves open.
Hydraulic lifters have a range of operation, the idea is for the oil inside to take up slack so the push rod is always seated snugly, yet when called upon to open the valve it does so without bleeding off.
Joe
