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

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

MODELS AFFECTED: 1991-1992 BROUGHAMS WITH 5.7L V8 ENGIN-E (VIN 7)

Some owners of 1991-1992 Broughams equipped with 5.7L V8 engines (RPO L05 - VIN 7) may comment of engine cold "piston slap" noise. This bulletin covers all 1991 - 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 of 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 dependant upon the piston/cylinder bore fit and block temperatures.

This condition may be caused by improper piston/cylinder bore fit.

To correct this condition 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 P/N ----------- --- 5.7L V8 Goodwrench Engine Assembly (Passenger Car) 12513151

NOTE: Remove the oil pan from the original engine and install it on the Goodwrench engine assembly.

Parts are currently available from GMSPO.

For warranty purposes use Labor Operation J1840.

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

Parts are currently available from GMSPO.

For warranty purposes use labor time from the J1300 group from the appropriate model year Labor Time Guide.

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.