GMC Powertrain 4.3 L, Service Manual, Page: 23 / 196

Engine Marine/Industrial 4.3L 6-13
2000 Marine/Industrial
Valve Train Diagnosis
General Information
Symptoms Cause
A light tapping noise at 1/2 engine speed, or any varying frequency, may indicate a valve train problem.
Tapping noises will typically increase with increased engine speed.
Before attempting to diagnose a valve train noise, check for the proper engine oil level and then allow the engine to
obtain normal operating temperature.
Following this procedure will bring all engine components to a normal state of expansion.
Sit in the driver’s seat, then operate the engine at various speeds and listen for any abnormal engine noise.
Valve Train Noise Low engine oil pressure
A worn or faulty oil pump
A loose or plugged oil pump screen
Loose valve rocker arm attachments (causing excessive valve lash)
A worn or damaged valve rocker arm ball
A worn valve rocker arm and/or valve pushrod
A broken valve spring
Sticking valves
Valve lifters worn, dirty or faulty
A broken valve lifter guide
Engine camshaft lobes worn
Worn valve guides or valve stems
Bent valve pushrods
Excessive free play in the camshaft timing chain
Bent, broken or damaged camshaft sprocket teeth
DEFINITION: A light tapping noise at 1/2 engine speed, or any varying frequency.
1
Is there valve train noise?
— Go to Step 2 System OK
Check for a high engine oil level. An engine with the
engine oil level above the FULL mark on the oil level
indicator allows the crankshaft counterweights to churn the
2 engine oil into foam. When the foamy engine oil is pumped
into the valve lifters, the valve lifters become noisy. A solid
column of engine oil ensures proper valve lifter operation.
Is the engine oil level too high? — Go to Step 3 Go to Step 4
3
Drain the engine oil to the proper level.
Is the tapping noise gone? — System OK Go to Step 6
Check for a low engine oil level. An engine with the engine
oil level below the ADD mark on the oil level indicator may
4 allow the oil pump to pump air at high engine RPM.
Is the engine oil level below the ADD mark on the oil level
indicator?
— Go to Step 5 Go to Step 6
5
Add the engine oil as required.
Is the tapping noise gone? — System OK Go to Step 6
Check for the proper engine oil pressure. Refer to Engine
6
Mechanical Specifications and Oil Pressure Diagnosis and
41.4 kPa
Testing. (6 psi)
Is the engine oil pressure within specifications?
Go to Step 11 Go to Step 7
Diagnostic Table
Step Action Value(s) Yes No