- Preliminary Diagnosis

A light tapping at one-half engine speed, or any varying frequency, can indicate a valve train problem. These tapping noises increase with engine speed. Before attempting to judge the valve train noises thoroughly warm up the engine. By doing this you will bring all engine components to a nominal state of expansion. Also, run the engine at various speeds and listen for engine noise with the hood closed while sitting in the driver's seat. The causes of the valve train noise include the following conditions:
^ Incorrectly adjusted valve lash
^ Low oil pressure
^ Loose valve rocker arm attachments
^ Worn valve rocker arm and/or pushrod
^ Broken valve spring
^ Sticking valves
^ Lifters worn, dirty or faulty
^ Camshaft lobes worn
^ Worn valve guides
^ Worn or damaged valve keys
^ Bent pushrods