TIMING GEAR NOISE/KNOCK 2.5L INFORMATION

VEHICLES AFFECTED: 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 No. 3 and No. 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 .0381 mm to .127mm (.0015 in. to 0050 in.).

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 camahaft gear back and forth. Camshaft gear backlash should be .0127 mm to .2413 mm (.0005 in. to .0095 in.). Check the backlash in four (4) areas 90 degrees apart.

7. If the camshaft end clearance exceeds .127 mm (.0050 in.) or gear backlash exceeds .2413 mm (.0095 in.) in the above checks, the timing gears and/or thrust plate should be replaced.

8. If gear lash exceeds the .2413 mm (.0095 in.) specified, replace both the camshaft and crankshaft gears.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.