Valve Mechanism or Valve Train Noise
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. Warm up the engine before attempting to judge the valve train noise.
By doing this you will bring all engine components to a normal state of expansion.
While sitting in the driver's seat run the engine at various speeds and listen
for engine noise with the hood closed.
Caution: The following procedure is not recommended on engines with stainless
steel exhaust manifolds because manifold temperature will exceed the flash
point of the oil causing a fire with possible personal injury.
If the valve mechanism is abnormally noisy, remove the rocker arm covers
and use a stethoscope in order to determine which valves or valve train parts
are causing the noise. The causes of the valve mechanism noise include the
following conditions:
| • | Broken or weak valve springs |
| • | Sticking or warped valves |
| • | Dirty, stuck or worn valve lifters |
| • | Damaged or improperly machined camshaft lobes |
| • | Insufficient or poor oil supply to the valve train (low oil pressure) |
| • | Excessive valve stem to guide clearance |
| • | Loose or worn rocker arm attachments |
| • | Missing or improperly positioned lifter guides (roller lifter
engines) |
