Diagnosis And Testing - Hydraulic Lifter(S) Noise Diagnosis

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 the lash adjusters for sponginess while installed in the cylinder head. Press down on the rocker arm in a manner that could collapse 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. Refer to INSPECTION .
	Check the camshaft journals and the bearing bores for abnormal wear patterns, scoring, grooving, fatigue, pitting or a foreign material. Refer to CAMSHAFT, ENGINE, REMOVAL .
5. A plugged oil restrictor in the oil passages to the cylinder head(s).	5. Check the cylinder head oil passages for blockage. Clean or replace as necessary.
6. Worn valve guide(s).	6. Measure the valve stem-to-guide clearance. Refer to INSPECTION .
7. Rocker arm loose, adjuster stuck or at maximum extension and still leaves lash in the system.	7. See below:
-	(a) Check the camshaft journal and lobe for abnormal wear patterns, scoring, grooving, fatigue, pitting or a foreign material. Refer to CAMSHAFT, ENGINE, REMOVAL .
-	(b) Check the rocker arm(s) for proper alignment to the camshaft lobe(s) and valve stem(s). Refer to ROCKER ARM, VALVE, REMOVAL .
-	(c) Check the lash adjuster(s) for proper operation and replace as necessary. Refer to LIFTER(S), HYDRAULIC, REMOVAL .
8. Air ingested into the engine oil due to a broken or cracked oil pump pickup tube.	8. Check the pickup tube and replace as necessary. Refer to PICK-UP, OIL PUMP, REMOVAL .
9. Faulty lash adjuster.	9. Replace the lash adjuster(s). Refer to LIFTER(S), HYDRAULIC, REMOVAL .