Valve Train Analysis - Hydraulic Lash Adjusters

Engine

Valve Train Analysis - Hydraulic Lash Adjusters

Hydraulic lash adjuster noise can be caused by any of the following:

- Excessive hydraulic lash adjuster gap (collapsed)
- Incorrectly functioning hydraulic lash adjuster
- Air in lubrication system
- Excessive valve guide wear
- Low oil pressure

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

An incorrectly functioning hydraulic lash adjuster can be sticking, caused by contaminants or varnish inside the hydraulic lash adjuster. The hydraulic lash adjuster can have a check valve that is not functioning correctly, which can be caused by an obstruction, such as dirt or chips that prevent the check valve from closing, or a broken check valve spring. A hydraulic lash adjuster with a leakdown time out of specification can cause hydraulic lash adjuster noise. If no other cause for noisy hydraulic lash adjuster can be found, the leakdown rate should be checked and new hydraulic lash adjusters installed if found to be out of specification.

Assembled hydraulic lash adjusters can be tested with a commercially available 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.

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