FRAME CRACKS AT THE ENGINE MOUNT BRACKETS

SUBJECT: FRAME CRACKS AT THE ENGINE MOUNT BRACKETS (ADD REINFORCEMENT TO BRACKET)

MODELS: 1988-94 CHEVROLET AND GMC TRUCK SIERRA K MODELS

CONDITION:

SOME OF THE MODELS LISTED, WHEN SUBJECTED TO EXTREME FRAME FLEXING IN SEVERE DUTY APPLICATIONS, MAY EXPERIENCE CRACKS AROUND THE ENGINE MOUNT BRACKET. THE CRACKS MAY INITIATE AT BOTH FRONT AND REAR TAB WELDS AND EVENTUALLY PROPAGATE AROUND THE ENGINE MOUNT BRACKET (FIGURE 1).

CORRECTION:

ENGINE MOUNT BRACKET REINFORCEMENTS HAVE BEEN DEVELOPED FOR THE PURPOSE OF REDISTRIBUTING THE LOAD OF THE ENGINE AWAY FROM AREAS OF HIGH STRESS WHERE CRACK INITIATION HAS OCCURRED. THE PROCEDURE BELOW IS RECOMMENDED WHEN REPAIRING A CRACKED ENGINE MOUNT BRACKET.

THE FOLLOWING WELDING SPECIFICATIONS ARE RECOMMENDED:

GMAW - GAS METAL ARC WELDING USE: ELECTRODE E70S-3

SMAW - SHIELDED METAL ARC WELDING USE: ELECTRODE E7018

SERVICE PROCEDURE - LEFT ENGINE MOUNT BRACKET:

1. DISCONNECT THE NEGATIVE BATTERY CABLE. 2. RAISE THE VEHICLE AND SUPPORT WITH SUITABLE SAFETY STANDS. 3. REMOVE THE FRONT AXLE DIFFERENTIAL CARRIER ASSEMBLY FROM THE VEHICLE AS DESCRIBED IN SECTION 4C OF THE APPROPRIATE SERVICE MANUAL. 4. CLEAN THE ENGINE MOUNT BRACKET AREA WITH A WIRE BRUSH IN ORDER TO DETERMINE THE FULL EXTENT OF THE CRACKS. FOLLOWING SECTION 2A OF THE SERVICE MANUAL, REPAIR THE CRACKS AROUND THE ENGINE MOUNT. 5. GRIND THE WELDS CREATED IN STEP 4 SO THE WELDS ARE FLUSH WITH THE FRAME. 6. USING FIGURE 2 AS A GUIDE, CREATE A PLASTIC OR CARDBOARD TEMPLATE OF THE ENGINE MOUNT REINFORCEMENT. THIS TEMPLATE WILL BE USED WHEN CONSTRUCTING THE ENGINE MOUNT REINFORCEMENT LATER. DO NOT WORRY ABOUT THE BENT TAB OF THE REINFORCEMENT AT THIS TIME. 7. THE WIDTH OF THE CARDBOARD OR PLASTIC TEMPLATE WILL NEED TO BE ADJUSTED SO THAT IT FITS BETWEEN THE ENGINE MOUNT BRACKET LEGS AS SHOWN IN FIGURE 4. ADJUST THE WIDTH OF THE TEMPLATE AS NECESSARY SO THAT IT FITS FLUSH BETWEEN THE ENGINE MOUNT BRACKET LEGS. 8. ONCE THE WIDTH OF THE CARDBOARD OR PLASTIC TEMPLATE IS ADJUSTED TO THE APPROPRIATE SIZE, CUT A PIECE OF 4.5 MM (0.18 IN.) THICK, SAE 1008-1010 MILD STEEL USING THE TEMPLATE AS A GUIDE. BEND THE UPPER FINGER OF THE REINFORCEMENT SO THAT IT RESEMBLES THE BEND SHOWN IN FIGURE 2. 9. CLEAN THE ENGINE MOUNT BRACKET THOROUGHLY IN PREPARATION FOR WELDING. 10. PLACE THE REINFORCEMENT INTO THE POSITION AS SHOWN IN FIGURE 4. USING C-CLAMPS, OR VISE GRIPS, CLAMP THE BRACKET INTO POSITION. IT SHOULD BE NOTED THAT IT IS VERY IMPORTANT THAT THE BOTTOM OF THE REINFORCEMENT BE FLUSH WITH THE LOWER RADIUS OF THE FRAME RAIL (FIGURE 4). 11. WELD THE BRACKET REINFORCEMENT IN THE POSITIONS SHOWN IN FIGURE 2. 12. REINSTALL THE DIFFERENTIAL CARRIER ASSEMBLY FOLLOWING THE PROCEDURE IN SECTION 4C OF THE APPROPRIATE SERVICE MANUAL.

SERVICE PROCEDURE - RIGHT ENGINE MOUNT BRACKET:

1. DISCONNECT THE NEGATIVE BATTERY CABLE. 2. RAISE THE VEHICLE AND SUPPORT WITH SUITABLE SAFETY STANDS. 3. DISCONNECT THE RIGHT HALF SHAFT FROM THE DIFFERENTIAL CARRIER FOLLOWING THE PROCEDURE IN THE SERVICE MANUAL. MOVE THE HALF SHAFT OUT OF THE WAY IN ORDER TO PROVIDE ADEQUATE WORKING SPACE AT THE ENGINE MOUNT BRACKET. 4. CLEAN THE ENGINE MOUNT BRACKET AREA WITH A WIRE BRUSH IN ORDER TO DETERMINE THE FULL EXTENT OF THE CRACKS. FOLLOWING SECTION 2A OF THE SERVICE MANUAL, REPAIR THE CRACKS AROUND THE ENGINE MOUNT. 5. GRIND THE WELDS CREATED IN STEP 4 SO THE WELDS ARE FLUSH WITH THE FRAME. 6. USING FIGURE 3 AS A GUIDE, CREATE A PLASTIC OR CARDBOARD TEMPLATE OF THE ENGINE MOUNT REINFORCEMENT. THIS TEMPLATE WILL BE USED WHEN CONSTRUCTING THE ENGINE MOUNT REINFORCEMENT LATER. DO NOT WORRY ABOUT THE BENT TAB OF THE REINFORCEMENT AT THIS TIME. 7. THE WIDTH OF THE CARDBOARD OR PLASTIC TEMPLATE WILL NEED TO BE ADJUSTED SO THAT IT FITS BETWEEN THE ENGINE MOUNT BRACKET LEGS AS SHOWN IN FIGURE 4. ADJUST THE WIDTH OF THE TEMPLATE AS NECESSARY SO THAT IT FITS FLUSH BETWEEN THE ENGINE MOUNT BRACKET LEGS. 8. ONCE THE WIDTH OF THE CARDBOARD OR PLASTIC TEMPLATE IS ADJUSTED TO THE APPROPRIATE SIZE, CUT A PIECE OF 4 MM THICK, 1008-1010 MILD STEEL USING THE TEMPLATE AS A GUIDE. BEND THE UPPER FINGER OF THE REINFORCEMENT SO THAT IT RESEMBLES THE BEND SHOWN IN FIGURE 3. ON SOME 1991 AND PRIOR MODEL YEAR TRUCKS THE UPPER FINGER OF THE REINFORCEMENT MAY NEED TO BE ADJUSTED TO PROVIDE A SUFFICIENT WELDING AREA. 9. CLEAN THE ENGINE MOUNT BRACKET THOROUGHLY IN PREPARATION FOR WELDING. 10. PLACE THE REINFORCEMENT INTO THE POSITION AS SHOWN IN FIGURE 4. USING C-CLAMPS, OR VISE GRIPS, CLAMP THE BRACKET INTO POSITION. IT SHOULD BE NOTED THAT IT IS VERY IMPORTANT THAT THE BOTTOM OF THE REINFORCEMENT BE FLUSH WITH THE LOWER RADIUS OF THE FRAME RAIL (FIGURE 4). 11. WELD THE BRACKET REINFORCEMENT IN THE POSITIONS SHOWN IN FIGURE 5. 12. REINSTALL THE HALF SHAFT TO THE DIFFERENTIAL CARRIER.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP DESCRIPTION LABOR TIME

J1487 INSTALL ENGINE MOUNT BRACKET REINF.- RIGHT USE PUBLISHED J1488 INSTALL ENGINE MOUNT BRACKET REINF. - LEFT LABOR OPERATION TIME

NOTE: LABOR OPERATION IS CODED TO BASE VEHICLE COVERAGE IN THE WARRANTY SYSTEM.

FIGURES: 5

CAPTIONS: FIGURE 1 - ENGINE MOUNT BRACKET CRACKS FIGURE 2 - LEFT SIDE ENGINE MOUNT BRACKET REINFORCEMENT TEMPLATE FIGURE 3 - RIGHT SIDE ENGINE MOUNT BRACKET REINFORCEMENT TEMPLATE FIGURE 4 - LOCATING THE ENGINE MOUNT BRACKET REINFORCEMENT FIGURE 5 - WELDING POSITIONS

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.

COPYRIGHT 1994 GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.