Lifter / Lash Adjuster: Description and Operation

Fig. 4 Hydraulic valve lifter:

Failure of a hydraulic valve lifter, Fig. 4, is generally caused by an inadequate oil supply or dirt. An air leak at the intake side of the oil pump or excessive oil in the engine will produce air bubbles in the oil supply to the lifters, causing them to collapse. This is a probable cause of trouble when several lifters fail to function, but air in oil is not likely to cause failure of a single unit.
Valve lifters can be removed after removing rocker arm cover, intake manifold and pushrod cover. Loosen rocker arm stud nut and rotate rocker arm so pushrod can be removed, then remove valve lifter. It may be necessary to use tool No. J-3049 to facilitate lifter removal.