ENGINE NOISE (INSTALL NEW DESIGNCAST IRON EXHAUST

REVISION: 02/03/98

THIS BULLETIN IS BEING REVISED TO CHANGE PART DESCRIPTION INFORMATION FOR CLARIFICATION. PLEASE DISCARD CORPORATE BULLETIN NUMBER 67-61-21 (SECTION 6-ENGINE). ______________________________________________________________________

REVISION: 02/17/98

THIS BULLETIN IS BEING REVISED TO ADD THE GMC LOGO WHICH WAS INADVERTENTLY OMITTED. PLEASE DISCARD CORPORATE BULLETIN NUMBER 67-61-21A (SECTION 6 - ENGINE). ______________________________________________________________________

SUBJECT: ENGINE NOISE (INSTALL NEW DESIGN CAST IRON EXHAUST MANIFOLD, STAINLESS STEEL GASKET AND ATTACHING HARDWARE)

MODELS: 1991-95 CHEVROLET AND GMC C6, C7, B7, P CHASSIS MODELS WITH 6.0L AND 7.0L ENGINES (VINS P, M - RPOS LS0, LR0)

CONDITION:

SOME OWNERS OF THE ABOVE MENTIONED VEHICLES MAY COMMENT ON ENGINE EXHAUST NOISE WHICH IS NORMALLY LOUDEST DURING COLD ENGINE OPERATION.

CAUSE:

AN EXHAUST LEAK MAY HAVE DEVELOPED BETWEEN THE CAST IRON EXHAUST HEAD AND THE ENGINE'S CYLINDER HEAD MATING SURFACE CAUSING THE CAST IRON EXHAUST MANIFOLD TO WARP AND/OR CRACK AT THE OUTBOARD FLANGES.

CORRECTION:

A NEW EXHAUST MANIFOLD, STAINLESS STEEL GASKET AND ATTACHING HARDWARE HAS BEEN DEVELOPED TO CORRECT THIS CONDITION. REPLACE THE EXISTING CAST IRON EXHAUST MANIFOLD AND GASKET WITH THE NEW DESIGN EXHAUST MANIFOLD, NEW STAINLESS STEEL GASKET AND NEW ATTACHING HARDWARE. DISCARD THE EXISTING ATTACHING HARDWARE SINCE IT WILL NOT BE REUSED.

INSTALLATION PROCEDURE 1. INSTALL NEW STUDS (1). TORQUE STUDS TO 30 N.M (22 LB FT) (FIGURE 1). 2. INSTALL NEW STAINLESS STEEL GASKET (2). 3. INSTALL NEW EXHAUST MANIFOLD (3). 4. INSTALL NEW NUTS (4) AND BOLT (5). THE BOLT IS TO BE INSTALLED IN THE NO. 4 POSITION RIGHT SIDE OF ENGINE. TORQUE NUTS TO 30 N.M (22 LB FT) TORQUE BOLT TO 54 N.M (40 LB FT) 5. INSTALL OIL LEVEL INDICATOR TUBE AND SPARK PLUG SHIELD (1) (FIGURE 2). 6. INSTALL NEW SPARK PLUG SHIELD ATTACHING NUTS (2). TORQUE NUTS TO 20 N.M (15 LB FT).

SERVICE PARTS INFORMATION REFER TO THE FOLLOWING PART NUMBERS WHENEVER REPLACEMENT OF THE EXHAUST MANIFOLD IS NECESSARY.

PART NUMBER DESCRIPTION QTY. REQUIRED

12551387 EXHAUST MANIFOLD-RIGHT 1 12551385 EXHAUST MANIFOLD-LEFT 1 9442946 NUT (EXHAUST MANIFOLD) 15 3909821 BOLT 1 12551449 GASKET 2 12554867 STUD 15 9442958 NUT (SPARK PLUG SHIELD) 8

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION DESCRIPTION

J0100 MANIFOLD, EXHAUST RH-REPLACE J0101 MANIFOLD, EXHAUST LH-REPLACE

USE PUBLISHED LABOR OPERATION TIME.

FIGURES: 2 ATTACHMENTS: 0

FIGURE 1 1. INSTALL NEW STUDS 2. INSTALL NEW STAINLESS STEEL GASKET 3. INSTALL NEW EXHAUST MANIFOLD 4. INSTALL NEW NUTS 5. INSTALL NEW BOLT

FIGURE 2 1. INSTALL OIL LEVEL INDICATOR TUBE AND SPARK PLUG SHIELD 2. INSTALL NEW SPARK PLUG SHIELD ATTACHING NUTS

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.

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