Valve lifters come in two types: adjustable and hydraulic. Both types of lifters provide the opening and closing of the exhaust and intake valves by contact with the camshaft. Hydraulic lifters use oil in their body housings to maintain a certain pressurised height, which determines the opening length of the valves. The adjustable valve lifter can be adjusted to determine the height of the valve opening. Both types of lifters need proper oil pressure and lubrication to work correctly. The vehicle owner can check his lifter operation using some basic tools.
Place the vehicle in park or neutral, depending upon your transmission type. Apply the emergency brake. Start the engine and let it warm up to normal operating temperature. Look at the dashboard for any red "Check Engine," or "Oil" light. If you have an original equipment oil pressure gauge, note the reading in psi (pounds per square inch). A warning light will be your first indication that you might have low oil pressure affecting your lifters.
Note the reading on the oil pressure gauge, if so equipped. Refer to your owner's manual for the proper oil pressure reading you should have. For instance, if you have a recommended oil pressure of 40 psi, and your gauge reads 20 psi or lower, this could be the first indication that clogged passages exist somewhere in the upper valve train, which would effect lifter performance.
Listen for any "clicking" or "clacking" noises coming from the top of the engine, particularly near the valve covers, or just under the intake manifold plenum cover. To better hear the noises, place a stethoscope over the valve covers or plenum and move it from the front of the engine toward the back, listening every 6 inches or so. Any obvious clicking or clacking noise will indicate a maladjusted lifter or a worn hydraulic lifter. Too much air in a collapsed hydraulic lifter will also produce these sounds.
Shut the engine off, if you have found lifter noise. Raise the bonnet and pull the oil dipstick out of the tube. Wipe it with a rag and reinsert it. Pull it out and check the oil level. If the oil level reads below the minimum level line, or does not show at all, the lifter noise might result from lack of lubrication. Examine the oil for discolouration. Foamy, white, grey or tan oil will indicate oil contamination, or oil that has lost its viscosity and lubricating qualities.
Disconnect the negative battery cable with a socket. Follow your vehicle repair manual's instruction for removing the valve covers from the engine. Use a socket and wrench to remove the valve cover bolts and lift the valve covers off. If you have a four- or six-cylinder engine with a top engine case, use sockets, screwdrivers and fuel line wrenches to remove the needed components, including the fuel line, vacuum hoses, throttle linkage, sensor wires and any other components that impede the removal of the single cover or valve covers.
Connect the negative battery cable with a socket and wrench. Start the engine, but do not rev it. Let it idle. Make sure all tappets, push rods and valve springs move up and down. If you have solid lifters in your engine, consult your repair manual for the valve lash gap, expressed in thousands of an inch. Remember the lash setting for the intake and exhaust separately. Select a feeler gauge for the proper setting for the exhaust valve at the front of the engine.
Stick the feeler gauge into the space between the valve stem top and the rocker arm tappet. You should feel a slight drag when pulling the gauge back and forth. If the tappet is noisy, loosen the locknut on the top of the tappet with an end wrench.
Use a screwdriver and adjust the set screw clockwise to tighten the adjustment -- make sure the gap conforms to the proper feeler gauge setting according to your manual. Hold the set screw and tighten the tappet locknut. Adjust each of the valves this way.
Loosen the tappet locknut with an end wrench, if you have hydraulic lifters. Use a screwdriver to loosen the set screw counterclockwise until the tappet begins to clack. Turn the set screw clockwise three-quarters of a turn and tighten the locknut with an end wrench. You will not need to use a feeler gauge with this method.
Watch for any tappet that remains clacking after you adjust a hydraulic valve this way. If any tappet produces noise, even after you exceed three-quarters of a turn in (clockwise), it will indicate a collapsed or excessively worn lifter. Those lifters must be replaced.
Change your oil filter and oil if you have very low oil pressure, but the dipstick level remains within specifications. A clogged oil filter will not allow the proper oil pressure to reach the upper parts of the valve train for proper lubrication. A worn oil pump will also produce lower oil pressure readings, and could cause valve train noise at idle or at higher speed ranges.
Tappets, valve springs and push rods that do not move while the engine is running could indicate a broken valve train part. Shut the engine off immediately if you encounter this symptom. Major engine repair will be required.