Noise

Valve tappet noise may be caused by any of the following:
- Air in lubrication system.
- Excessive collapsed valve tappet gap (valve clearance).
- Excessive valve guide clearance.
- Leakdown rate too rapid.
- Sticking valve tappet plunger.
- Valve tappet check valve not functioning properly.
- Worn adjustment shims.
- Worn camshaft lobes.
- Worn rocker arms (roller followers).

Excessive Collapsed Valve Tappet Gap
May be caused by loose rocker arm seat bolts, incorrect initial adjustment, or wear of valve tappet face, roller valve tappets, push rods, rocker arms, rocker arm seat or valve tip. With valve tappet collapsed, check gap between valve tip and rocker arm and/or camshaft lobe (depending upon application) to determine if any other valve train parts are damaged, worn or out of adjustment.

Sticking Hydraulic 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 debris causing the condition.

Hydraulic Valve Tappet Check Valve
A hydraulic 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 cam lobe is lifting the valve tappet. It may also be caused by a broken check valve spring.

Air Bubbles In The Lubrication System
This will prevent the valve tappet from supporting the valve spring load and may be caused by too high or low of an oil level in the oil pan (6675). It may also be caused by air being drawn into the system through a hole, crack or leaking O-rings on the oil pump screen cover and tube (6622).

Valve Tappet Leakdown Rate
If the Leakdown time is below the specified time for used hydraulic valve tappets, noise may result. If no other cause for noisy hydraulic valve tappets can be found, check the Leakdown rate and replace any hydraulic valve tappets outside the specification.