Two types of lifters are used in automotive engines: the hydraulic type which uses oil inside the lifter body to keep the valve lash within specifications, and the solid lifter which has no hydraulic system, which you must adjust manually. Lifters open and close the intake and exhaust valves and are subject to wear just like any other automotive component. Knowing what causes lifters to go bad can save a vehicle owner the major expense of engine rebuilding, should the lifters fail completely.
Older engines with high mileage are prime candidates for the beginning signs of lifter wear, whether hydraulic or solid in design. Coupled with poor maintenance that involves infrequent oil and filter changes, lifter wear accelerates proportionately because of neglect, and can only worsen. The valve train parts, particularly the lifters, depend solely on the condition and level of the oil, since they cannot function without it, even for brief periods. Contaminated oil in a high-mileage engine wears the lifter bottom, cam lobe, push rod seat and internal lifter parts.
Valve lifters will starve for lubrication if the oil crankcase level is too low to provide sufficient oil pressure to reach the upper valve train parts. If the oil pickup screen cannot pull oil even temporarily, the lifters may suffer lack of lubrication. Hydraulic lifters can collapse, with no oil cushion to dampen the pounding from the tappet or push rod. Solid lifters can wear on their camshaft side, along with the camshaft lobes. Too much oil in the crankcase can cause oil aeration, or air bubbles, a condition when the crankshaft churns up the oil by direct contact. Contaminated oil will clog hollow push rod passages and hydraulic lifter orifices, disallowing lifter function.
The proper oil viscosity rating is important for reducing component wear and maintaining good engine performance. The heavy viscosity oils, like 40W and 20W-50, promote good oil pressure in hotter weather but their flow rate, the ability of the oil to flow to all of the components on the engine, may be insufficient in cold weather, especially during initial startup. This especially applies to overhead cam engines, where the oil must travel farther vertically. Light viscosity oils, such a 5W-20 or straight 10W, can flow more readily in colder temperatures, but are too thin to provide proper lubrication and pressure in hot environments. Many manufactures recommend 5W-30 as an adequate all-season motor oil.
Oil filters that have not been changed during regular intervals can clog and impede or stop the oil flow, reducing oil pressure. This can be seen as a flickering or steady oil warning dash light that shows "Check Engine" or "Oil Pressure." Clogged or dirty oil pump pickup screens will also cause low oil pressure and impede or stop oil from reaching the upper valve train parts.
Hydraulic lifters are set to "zero" lash, in that the pressure exerted upon them is absorbed by the cushion of oil inside their body casing. A tappet nut that has backed off of its recommended setting will cause a hammering on the lifter by either the cam or push rod. The constant hammering will induce metal wear and further change the lash tolerances and increase wear. Solid lifters must be adjusted periodically, at every 30,000 miles or so. If the lash or gap in the solid lifter adjustment is off, it can cause lifter and cam wear. Bent push rods will also alter the lash adjustment and must be replaced.
Valve lifters are one of the first components to suffer wear when the oil pressure is consistently low. Low oil pressure can result from a number of factors, including excessive camshaft end play and worn cam bearings, worn oil pump gears, worn crankshaft journals and bearings and worn main and rod bearings. Any small oil passage in the engine can restrict flow and cause low oil pressure. Low oil pressure shows up as a dash warning light or oil pressure gauge reading.
Worn lifters, or excessively low oil pressure, will often produce a clacking or clicking sound, especially during engine warmup. The sound originates from collapsed hydraulic lifters that are frozen, or from solid lifters that have worn excessively and changed lash tolerances. An engine miss usually accompanies a bad lifter, usually originating from the affected cylinder. Lifter noises should not be confused with arcing or snapping spark plug wires.
