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

SUBJECT: METALLIC KNOCK SOUND WHEN ENGINE COLD (REPLACE PISTON/ ENGINE)

VEHICLES AFFECTED: 1991-92 "B AND D" MODELS W/5.7L (L05) ENGINE AND A/T

THIS BULLETIN SUPERSEDES AND REPLACES CORPORATE BULLETIN REFERENCE NUMBER 376004.** THIS BULLETIN IS BEING REVISED TO CHANGE THE CANADIAN BULLETIN NUMBER FROM 93-6-119 TO 93-6-122.

CONDITION:

--------- Some owners of 1991-92 B and D 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 4 degrees Celsius (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:

Description Part Number ----------- ----------- 5.7L V8 Goodwrench Engine 12513151 Assembly (Passenger Car)

NOTE: On "D Model" applications, remove the oil pan from the original engine and install it on the Goodwrench Engine Assembly.

For vehicles repaired under warranty use:

Body Type Labour Time Code Time --------- ---------------- ---- B Body J-1840 8.6 Hours w/Engine Oil Cooler 0.2 Hour D Body J-1840 Use published Labor Time

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

Description Part Number ----------- ----------- Piston/Standard Size 10159436 Piston/High Limit Size 10159437

For vehicles repaired under warranty use:

Use Published Labour 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.