For 1990-2009 cars

# TIMING GEAR KNOCK NOISE FURTHER DIAGNOSIS

#### SUBJECT: TIMING GEAR NOISE (KNOCK)

#### MODELS AFFECTED: SOME 1985 THRU 1987 MODELS EQUIPPED WITH 2.5L L-4 ENGINES (VIN CODES R AND U)

If an engine has a knock and the preliminary diagnosis is a "cam gear knock", use the normal procedure described in Buick bulletin 85-6-18, to check camshaft end clearance and gear backlash.

Measure the backlash at positions outside the two retainer plate access holes and at two other areas 90 degrees from these holes.

If end clearance is not beyond .0015" (.0381 mm) to .0050" (.127 mm) and backlash is not beyond .0005" (0.013 mm) to .0095" (0.241 mm) and the cam and crank gears are not damaged, the gears are not causing the knock. Examine the engine for other sources of knock.

If end clearance is less than .0015" (.0381 mm), replace the spacer ring; if it exceeds .0050" (.127 mm) , make certain the gear is seated properly against the spacer, and if it still exceeds .0050" (.127 mm) , replace the thrust plate.

If backlash is less than .0005" (.013 mm), or greater than .0095"(.241 mm), replace the cam and crank 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.