Engine - Metallic Knock Noise When Cold, Replace Piston

NUMBER: 92-T-173

CORP.REF.NO: 376004

DATE: July 1993

SECTION: 6A

SUBJECT:
METALLIC KNOCK SOUND WHEN ENGINE COLD - REPLACE PISTON/ENGINE

MODELS/YEARS:
1992 CUSTOM CRUISER W/5.7L (VIN 7) ENGINE AND A/T

CONDITION:
Some owners of 1992 Custom Cruiser models equipped with 5.7L V8 engines may comment of engine cold "piston slap" noise. This bulletin covers all 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~F 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:
Verity 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 P/N
5.7L V8 Goodwrench Engine 12513151
Assembly (Passenger Car)

WARRANTY INFORMATION:
Labor Time Code J-1840
Time 8.6 hours
w/Engine Oil Cooler 0.2 hour

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

Description P/N
Piston/Standard Size 10159436
Piston/High Limit Size 10159437

Parts are currently available from GMSPO.

WARRANTY INFORMATION: Use applicable Labor Time Guide.