Worn or loose rocker arms--the rocker arm bearing end caps and/or needle bearings should intact within the rocker arm assembly.

Replace the valve rocker arms as required.

Worn or bent pushrods

Replace the pushrods.

Stuck valves--carbon buildup on the valve stem can cause the valve not to close properly.

Repair or replace as required.

Excessively worn or mis-aligned timing chain

Replace the timing chain and sprockets as required.

Worn camshaft lobes

Replace the camshaft and valve lifters.

Sticking lifters

Replace as required.

Excessive engine oil pressure

Perform an oil pressure diagnosis. Refer to Oil Pressure Diagnosis and Testing .