METALLIC KNOCK SOUND WHEN ENGINE COLD(REPL. PISTON/ENG.)

Subject: METALLIC KNOCK SOUND WHEN ENGINE IS COLD

Model and Year: 1991-92 CAPRICE WITH 5.7 L ENGINE AND AUTOMATIC TRANSMISSION

CONDITION:

--------- Some owners of 1991-92 B cars equipped with 5.7L V8 engines (RPO L05 - VIN 7) may comment of engine cold "Piston slap" noise. This bulletin covers all 1991 and 1992 production through May of 1992.

NOTE: This noise will not result in engine failure, but may be a customer annoyance condition.

Engine cold "piston slap" may be described as:

A metallic "knock" sound that diminishes as the engine warms up. The knock sound is most noticeable at 1500 through 2000 engine RPM, with the engine at a light load. Duration of the "knock" varies depending on the engine block temperature. Temperatures of 40 degrees Fahrenheit or less may result in a knock duration as long as 5 to 8 minutes. Intensity of the knock will be dependent upon the piston/cylinder bore fit and block temperature.

CAUSE:

----- Improper piston/cylinder bore fit.

CORRECTION:

---------- Verify that the "piston slap - engine cold" condition is correctly identified.

Two methods of resolving this problem are available.

Preferred Method: A 5.7L V8 (VIN 7) "Goodwrench" Engine Assembly (for passenger car application only) has been released to address this concern:

PART NO. DESCRIPTION -------- ----------- 12513151 5.7L V8 Goodwrench Engine Assembly (Passenger Car)

Parts are currently available from GMSPO.

WARRANTY INFORMATION:

BODY TYPE LABOR OP TIME --------- -------- ---- B Body J1840 See w/Engine Oil Applicable Cooler LTG

Optional Method: Replace the "slapping" piston(s) with new pistons of improved design. Pistons are available in "standard' and "high limit" sizes as follows:

PART NO. DESCRIPTION -------- ----------- 10159436 Piston/Standard Size 10159437 Piston/High Limit Size

Parts are currently available from GM

Use standard Labor Time Codes and Times.

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.