INFO - PREMATURE MAIN BEARING FAILURE

SUBJECT: INFORMATION - PREMATURE MAIN BEARING FAILURE

MODELS: 1996-98 CHEVROLET AND GMC C/K, M/L, S/T, G, P TRUCKS 1996-98 OLDSMOBILE BRAVADA WITH 4.3L V6 ENGINE (VINS W, X - RPOS L35, LF6)

THERE HAVE BEEN SEVERAL REPORTS FROM THE FIELD (TAS) OF SOME 4.3L V6'S EXPERIENCING PREMATURE ENGINE MAIN BEARING FAILURE. IN MOST OF THESE CASES, THIS CONDITION HAS OCCURRED SOON AFTER AN INLET MANIFOLD R+R PROCEDURE.

IN 1996, THE GEN 1 V6 ENGINES WERE RE-ENGINEERED TO INCORPORATE "VERTICAL" INLET MANIFOLD-TO-CYLINDER HEAD ATTACHING BOLTS. IF THE INLET MANIFOLD BOLTS ARE OVER TORQUED, THE CRANKSHAFT MAIN BEARING BORE WILL BE DISTORTED, ELIMINATING THE NECESSARY CLEARANCE FOR PROPER OIL FILM.

NOTICE: IF INLET MANIFOLD ATTACHING BOLT TORQUE AND TIGHTENING SEQUENCE ARE NOT STRICTLY ADHERED TO, PER THE SERVICE MANUAL, CRANKSHAFT MAIN BEARING BORE ALIGNMENT CAN BE DISTORTED WITH CRANKSHAFT MAIN BEARING FAILURE BEING THE END RESULT.

IMPORTANT: 1. ALWAYS FOLLOW PUBLISHED INLET MANIFOLD SERVICE PROCEDURES. 2. DO NOT OVERTORQUE INLET MANIFOLD-TO-CYLINDER HEAD ATTACHING BOLTS. 3. DO NOT DEVIATE FROM THE PUBLISHED BOLT TIGHTENING TORQUE SEQUENCE.

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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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