Engine - Metallic Knock Sound When Cold
Number: 92-358A-6Section: 6
Date: JULY 1993
Corporate Bulletin No.: 376004
ASE No.: A1, A8
Subject:
METALLIC KNOCK SOUND WHEN ENGINE IS COLD
Model and Year:
1991-92 CAPRICE WITH 5.7L ENGINE AND
AUTOMATIC TRANSMISSION
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 40 degrees 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:
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:
WARRANTY INFORMATION:
Optional MQM: Replace the "slapping" piston(s) with new pistons of improved design. Pistons are available in "standard" and "high limit" sizes as follows:
Use standard Labor Time Codes and Times.