Fiero L4-151 2.5L (1985)
Camshaft Gear/Sprocket: All Technical Service Bulletins
Engine - Timing Gear Noise Diagnosis
Number 85-6(Gasoline)-39 Date 6/85
Subject:
TIMING GEAR NOISE (KNOCK)
1985 2.5L L-4 ENGINES (ENGINE CODES R, U, 2)
The following information will outline characteristics of timing gear noise and assist in diagnosis.
TIMING GEAR NOISE - Loose or improperly seated camshaft 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 gear cover will give definite indication of timing gear noise.
Timing gear noise is most audible at about 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 rocker arms.
2.
Remove timing gear cover.
3.
Check camshaft end clearance to determine if gear is fully seated. End clearance should be .0015" (.0038 cm) to .0050" (.0127 cm)
4.
Install the crank pulley and torque the retaining bolt.
5.
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.
6.
Rotate the camshaft gear back and forth. Camshaft gear backlash should be .0005" (.0013 cm) to .0095" (.0241 cm). Check the backlash in four
(4) areas 90~ apart.
7.
If the camshaft end clearance exceeds .0050" (.0127 cm) or gear backlash exceeds .0095" (.0241 cm) in the above checks, the timing gears and/or
thrust plate should be replaced.
8.
If gear lash exceeds the .0095" (.0241 cm) specified, replace both the camshaft and crankshaft gears.