Engine Noise Diagnosis (Valve Train) - GMC chervolet camaro 1999 Service Manual

6-22 Engine Mechanical - -3.8 L
Knocks Cold and Continues for 2 to 3 Minutes
Cold engine knock usually disappears when the
specific cylinder secondary ignition circuit is grounded
out. Cold engine piston knock which disappears
in 1 .5 minutes should be considered acceptable.
• Engine flywheel contacting the transmission
converter cover - reposition the
transmission converter cover.
• Loose. or broken crankshaft balancer or the drive
pulleys - tighten or replace the crankshaft·
balancer or the drive pulleys as necessary.
• Excessive piston-to-bore clearance - replace the
piston.
• Bent connecting rod - replace the connecting rod.
Knocks at Idle Hot
• Inspect the drive belt for wear. Check the tension
and/or replace as necessary.
• Inspect the A/C compressor or generator bearing.
Replace or repair as necessary.
• Inspect the valve train. Replace the parts as
necessary.
• Inspect for improper oil viscosity. Install the proper
viscosity oil for the expected temperature. Refer
to Maintenance and Lubrication for the engine
oil specifications.
• Inspect for excessive piston pin clearance.
Replace the piston and the pin as necessary.
• Inspect the connecting rod alignment. Check and
replace the connecting rods as necessary.
• Inspect for insufficient piston-to-bore clearance.
Hone the bore and fit the new piston.
• Inspect the crankshaft balancer for looseness.
Tighten and/or replace the worn parts.
• Ensure that the piston pin is not offset to the
wrong side. Properly install the piston.
• Ensure that the camshaft drive gear backlash is
not excessive. The knock will also be heard on
a cold engine.
Knocks on Start-Up but Only Lasts a
Few Seconds · · ·
The following conditions may produce engine knocks
on initial start-up, but only last a few seconds:
· • Improper oil viscosity
- Install the proper oil viscosity for the
expected temperatures.
- Refer to Maintenance·and Lubrication.
• Utter bleed down - clean, test, and replace the
lifter as necessary.
- When the engine is off, some valves will be
open. Spring pressure against the lifters will
tend to bleed the lifter down. Repair the
lifter only if the problem is consistent.
- Engines operated for only short periods
between start-ups may have lifter noise that
lasts for a few seconds. This is a normal
condition.
Engine
• Excessive crankshaft end play - replace the
crankshaft thrust bearing.
• Excessive front main bearing clearance - replace
the worn parts.
• Timing chain tensioner malfunction - clean,
inspect and, replace the timing chain tensioner, if
required. ·
Heavy Knock Hot in Heavy Load Condition
• Broken crankshaft balancer or pulley hub -
replace the parts as necessary.
• Loose torque converter bolts - tighten the bolts.
• The drive belt is too tight or nicked - replace
the drive belt as necessary. ·
• The exhaust system is grounded - reposition the
exhaust system components as necessary.
• The flywheel is cracked - replace the flywheel.
• Excessive crankshaft main bearing clearance
- replace the crankshaft main bearings as
necessary.
• Excessive connecting rod bearing clearance -
replace the connecting rod bearings as
necessary.
Light Knock Hot in Light Load Condition
Light knock hot may be caused by one or more of the
following conditions:
• Loose torque converter bolts - tighten the torque
converter bolts.
• Leak at the exhaust manifold - tighten the bolts
and replace the exhaust manifold gasket if
necessary.
• Excessive connecting rod bearing clearance -
replace the connecting rod bearings as
necessary.
• Detonation or spark knock, refer to Engine
Controls.
Engine Noise Diagnosis (Valve Train)
A light tapping at one-half engine speed, or any
varying frequency, can indicate a valve train problem.
These tapping noises increase with the engine .
speed. Warm up the engine before attempting to judge
the valve train noise. This will bring all of the engine
components to a normal state of expansion. 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 to
determine which valve train components are causing
the noise. The causes of the valve noise include
the following conditions:
• Broken or weak valve springs
• Sticking or warped valves
• Bent push rods
(