Hydraulic Lash Adjuster

A tappet-like noise may be produced from several sources. Check the following items:

• Engine oil level too high or too low. This may cause oil aeration. Aerated oil entering the adjusters may cause them to be spongy.
• Insufficient running time after rebuilding the cylinder head. Low speed running up to one hour may be required. Turn the engine off and let set for a few minutes before restarting. Repeat this several times after the engine has reached normal operating temperature.
• Low oil pressure.
• The oil screen in cylinder head or the oil passage to the cylinder head is plugged with debris.
• Air ingested into oil due to broken or cracked oil pump pick-up.
• Worn valve guides.
• Rocker arm ears contacting valve spring retainer.
• Rocker arm loose, adjuster stuck or at maximum extension and still leaves lash in the system.
• Oil leak or excessive cam bearing wear in the cylinder head.
• Faulty lash adjuster. Check lash adjusters for "sponginess" while installed in the cylinder head and cam lobe at base circle. Depress part of rocker arm over the adjuster. Normal adjusters should feel firm when pressed quickly. When pressed very slowly, lash adjusters should collapse. Remove suspected lash adjusters and replace. Before installation, make sure adjusters are full of oil. This can be verified by little plunger travel when lash adjuster is depressed quickly.