Diagnosis And Testing - Lash Adjuster (Tappet) Noise

WARNING: This page is about a different variant/trim than selected.

Proper noise diagnosis is essential in locating the source of an NVH complaint. Locating a lash adjuster (tappet) type noise can sometimes be difficult. As a result, an initial misdiagnosis may occur.

Refer to the following chart for possible causes and correction of a lash adjuster (tappet) type noise.

LASH ADJUSTER (TAPPET) NOISE CHART

POSSIBLE CAUSES	CORRECTION
1. Engine oil level-too high or too low. This may allow aerated oil to enter the adjusters and cause them to be spongy.	1. Check and correct the engine oil level.
2. Insufficient running time after rebuilding a cylinder head.	2. Low speed running of up to 1 hour may be required to fully evacuate trapped air from the valve train system. During this time, turn engine off and let set for a few minutes before restarting. Repeat this several times after engine has reached normal operating temperature.
3. Air trapped in the lash adjuster (after 1 hour of run time).	3. See below:
	(a) Check lash adjusters for sponginess while installed in the cylinder head. Depress the lash adjuster. Normal adjusters should feel very firm. Very spongy adjusters can be bottomed out easily.
	(b) If the lash adjuster(s) are still spongy, replace the lash adjuster(s). Refer to LIFTER(S), HYDRAULIC, REMOVAL .
4. Low oil pressure.	4. See below:
	(a) Check and correct the engine oil level.
	(b) Check the engine oil pressure. Refer to DIAGNOSIS AND TESTING .
	(c) Check for excessive main bearing clearance and correct. Refer to STANDARD PROCEDURE .
	(d) Check for a worn oil pump.
5. Oil passage to the cylinder head(s) plugged with debris.	5. Check cylinder head oil passages for blockage. Clean or replace as necessary.
6. Worn valve guide(s).	6. Measure valve stem-to-guide clearance. Refer to INSPECTION .
7. Air ingested into oil due to broken or cracked oil pump pickup tube.	7. Inspect pickup tube and replace as necessary. Refer to PICK-UP, OIL PUMP, REMOVAL .
8. Collapsed lash adjuster due to debris ingestion.	Check lash adjuster while in the cylinder head. A normal lash adjuster will feel very firm. A lash adjuster with debris will be collapsed and will be very spongy. If the lash adjusters are easily collapsed, clean debris from the engine and replace the lash adjusters. Refer to LIFTER(S), HYDRAULIC, REMOVAL . .