As the miles pile upon a vehicle, parts start wearing out or requiring adjustment. The valve train is no exception; even the advent of hydraulic lifters has failed to eradicate the potential for valve train noises --- more commonly known as "tappet noises." Several possible causes exist for tappet noise, including improperly adjusted valves, worn rocker arms, bent push rods, worn valve guides and loose rocker arm studs. If the inspection of all these parts fails, the problem likely lies in the lifters. Before partially tearing down the engine and replacing lifters, take a few other steps to quiet noisy lifters.
Start the engine, let it warm up to operating temperature and then shut it off. Remove the engine oil dipstick. Wipe the dipstick off with a rag, then reinsert it all the way into the dipstick tube and pull it out again.
Inspect the oil level while the dipstick is out to ensure the engine doesn't contain an excessive amount of oil. Too much oil will cause the camshaft to churn in the oil, causing air bubbles in the system. If air bubbles enter the hydraulic lifters, the lifter will lack sufficient hydraulic pressure, causing it to make noise.
Inspect the oil on the dipstick for dirt, sludge, solid contaminants or excessive carbon content, noted by a blackening of the oil. Sludge in the oil pan will prevent the oil pickup tube inside the oil pan from the picking up the proper amount of oil to lubricate the engine. Change the oil and filter if necessary. Add one bottle of a penetrating oil product that breaks down sludge in the engine oil pan and the oiling system, including the oil journals. Lack of lubrication can cause lifter noise.
Remove the valve cover with whichever tools are necessary if you find no contaminants found in the engine oil. Start the engine.
Hold one end of a 2-foot length of heater hose against either ear while moving the other end of the hose from rocker arm to rocker arm, listening for tappet noises. Make note of the noisy rocker arms.
Adjust the valves to factory specifications. If the valves are out of adjustment, the lifters will make noise.
Loosen the rocker arm nut, and slide the rocker arm to the side if adjusting the valves does quiet the noisy lifters. Inspect the push rods to ensure that they are straight and not clogged with sludge. Replace any bent or clogged push rods, and adjust the valves again.
Remove the noisy lifters from the lifter bores in the engine, following the procedures laid out in the engine manufacturer's shop manual, if you find no defective push rods. Inspect them for external wear, and perform a leak down test on noisy lifters that do not show excessive wear (see the Tips section for details). Replace any lifters that show excessive external wear or fail a leak down test.
Disassemble the noisy lifters if they pass a leak down test: Compress the piston into the lifter, removing the snap ring that contains the piston inside the lifter with snap ring pliers and slowly releasing the spring pressure on the piston.
Remove the piston, spring and check ball from inside the lifter. Inspect the parts for excessive wear or breakage. Replace any defective lifters.
