A light tapping at one-half engine speed, or any varying
frequency, can indicate a valve train concern.
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 normal
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:
| • | Loose valve rocker arm attachments |
| • | Worn valve rocker arm and/or pushrod |
| • | Lifters worn, dirty or failed |
| • | Worn or damaged valve keys |
