COLD ENGINE TICK/RATTLE AFTER STARTUP (REPL. PISTONS & PINS). Buick Regal 1994

SUBJECT: COLD ENGINE TICK OR RATTLE AFTER START-UP (REPLACE PISTONS AND PINS)

MODELS: 1990-94 BUICK ELECTRA, LESABRE, REATTA, REGAL, RIVIERA AND PARK AVENUE 1990-94 OLDSMOBILE EIGHTY EIGHT, NINETY EIGHT AND TORONADO 1990-94 PONTIAC BONNEVILLE

1992-94 CHEVROLET LUMINA APV 1992-94 OLDSMOBILE SILHOUETTE 1992-94 PONTIAC TRANS SPORT WITH 3800 ENGINE (VIN L - RPO L27)

CONDITION:

PISTON PIN TICK OR RATTLE MAY BE DESCRIBED BY CUSTOMERS AS A TICKING NOISE THAT BEGINS SHORTLY AFTER COLD START-UP AND GRADUALLY DIMINISHES AS THE ENGINE WARMS UP. IN MOST CASES, THE NOISE IS GONE AFTER FIVE MINUTES. IN SEVERE CASES, THE NOISE MAY NOT DISAPPEAR WHEN THE ENGINE IS HOT.

PISTON PIN NOISE OCCURS IN BOTH PARK AND DRIVE AT IDLE RPM, VARYING IN INTENSITY DEPENDING ON THE NUMBER OF PISTONS INVOLVED. A TICKING SOUND MEANS ONE PISTON IS AFFECTED; A MARBLY RATTLE OR DIESEL-TYPE SOUND MEANS TWO OR MORE PISTONS ARE AFFECTED.

CAUSE:

THE SPECIFICATION FOR PISTON-TO-PIN CLEARANCE IS 0.0004 TO 0.0008 INCH (0.010 TO 0.020MM). STUDIES HAVE SHOWN THAT TRACE LEVELS OF NOISE CAN OCCUR BETWEEN 0.0006 AND 0.0008 INCH (0.015 TO 0.020MM). WHEN THE CLEARANCE IS AT 0.0008 (0.020MM), THE NOISE MAY BECOME AUDIBLE TO THE CUSTOMER.

**NOTE** TESTS HAVE ALSO SHOWN THAT PISTON PIN RATTLE DOES NOT HAVE ANY NEGATIVE EFFECTS ON SHORT TERM OR LONG TERM ENGINE DURABILITY.

CORRECTION:

IF PISTON PIN NOISE IS DETECTED AND THE CUSTOMER DESIRES THE CONDITION TO BE CORRECTED, REPLACE ALL SIX PISTONS AND PINS. THE NEW PISTON SETS HAVE MINIMAL PISTON-TO-PIN CLEARANCES.

SERVICE INFORMATION:

USE THE PROCEDURE OUTLINED IN THE APPROPRIATE SERVICE MANUAL FOR PISTON REPLACEMENT.

**NOTE** WHEN INSTALLING THE NEW PISTON AND PIN ASSEMBLY ONTO THE EXISTING RODS, USE EXTREME CARE TO AVOID DAMAGE TO EITHER THE PIN OR PISTON PIN BORE. IF DAMAGE TO THESE AREAS OCCUR, THE NOISE WILL RETURN BECAUSE THE DAMAGE WILL CAUSE WEAR AND EXCESSIVE CLEARANCE.

PARTS INFORMATION: PISTON ASSEMBLY APPLICATION PART NUMBER ----------- --------------- 1990-92, INCLUDING 1993 BUICK RIVIERA 12537198 1993-94 12537200

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

LABOR OPERATION: J1307 USE PUBLISHED LABOR OPERATION TIMES.

FIGURES: 0

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.