Worn or loose Stationary Hydraulic Lash Adjusters (SHLAs), valve rocker arms.

The SHLAs, valve rocker arm, roller bearing should be intact and in the correct position.

Replace the SHLAs, valve rocker arms, as required.

Sticking valves.

Carbon buildup on the valve stem can cause the valve not to close correctly.

Repair or replace as required.

Worn or mis-aligned above acceptable tolerances timing chain or chains.

Replace the timing chain or chains and sprockets as required.

Worn camshaft lobes.

Replace the camshaft or camshafts and high SHLAs, valve lifters.

Sticking SHLAs, lifters.

Replace the SHLAs as required.