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 valve 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 |
| • | Broken valve rocker arm stud |
| • | Loose or worn valve rocker arm attachments |
| • | Missing or improperly positioned valve lifter guides (roller valve
lifter engines) |
