Celebrity L4-151 2.5L (1982)
Camshaft Gear/Sprocket: Customer Interest
Timing Gear - Noise
Number:
83-T-18
Section:
VI
Date:
Feb., 1983
Subject:
TIMING GEAR NOISE (KNOCK) 2.5L L4 ENGINES - ALL YEARS
TO:
ALL CHEVROLET DEALERS
The following information will outline characteristics of timing gear noise and assist in diagnosis.
TIMING GEAR NOISE
Loose or improperly seated timing gears are usually loudest when warm. They are speed sensitive only, not load sensitive. Cam gear noise
will be evident at a warm idle and sounds much like a loose timing chain noise. Removing drive belts and placing a sounding device on the
timing pointer will give definite indication of timing gear noise.
Timing gear noise is most audible at 800 rpm. It can be heard the loudest at the timing gear cover and at the oil pan between #3 and #4
cylinders.
If an engine noise has been diagnosed as timing gear related, the following procedure for checking timing gear backlash should be followed.
1.
Remove rocker arm cover and loosen all rocker arm retaining nuts on pre-1981 vehicles and shouldered bolts on 1981 and later model
vehicles.
2.
Remove timing gear cover.
3.
Check camshaft end clearance to determine if gear is fully seated. End clearance should be .0015" to .0050".
4.
With a magnetic dial indicator positioned on the front face of the engine block, place the dial indicator on one tooth of the camshaft
gear.
5.
Rotate the camshaft gear back and forth. Camshaft gear backlash should not exceed .006".
6.
If camshaft end clearance exceeds .0050" or gear backlash exceeds .006" in the above checks, the timing gear should be replaced.
