Noise

Hydraulic valve tappet noise may be caused by any of the following:
^ excessive collapsed valve tappet gap sticking valve tappet plunger
^ valve tappet check valve not functioning properly
^ air in lubrication system
^ leakdown rate too rapid
^ excessive valve guide wear

Excessive collapsed valve tappet gap may be caused by loose rocker arm seat bolts/nuts, incorrect initial adjustment or wear of valve tappet face, or worn roller valve tappets, push rod, rocker arm, rocker arm seat or valve tip. With valve tappet collapsed, check gap between valve tip and rocker arm to determine if any other valve train parts are damaged, Worn or out of adjustment.

A sticking valve tappet plunger may be caused by dirt, chips or varnish inside the valve tappet. The sticking can be corrected by disassembling the valve tappet and removing the dirt, chips or varnish that are causing the condition.

A valve tappet check valve that is not functioning may be caused by an obstruction such as dirt or chips that prevent it from closing when the camshaft lobe is lifting the valve tappet. It may also be caused by a broken check valve spring.

Air bubbles in the lubrication system will prevent the valve tappet from supporting the valve spring load. This may be caused by too high or too low an oil level in the oil pan (6675) or by air being drawn into the system through a hole, crack or leaking gasket on the oil pump screen cover and tube (6622).

If the leakdown time is below the specified time for used valve tappets, noisy operation may result. If no other cause for noisy valve tappets can be found, the leakdown rate should be checked and any valve tappets outside the specification should be replaced.

Assembled valve tappets can be tested with a hydraulic tappet leakdown tester to check the leakdown rate. The leakdown rate specification is the time in seconds for the plunger to move a specified distance while under a 22.7 kg (50 lb) load. Test the valve tappets as follows.