INFORMATION ON COMPONENT AND SERVICE PROCEDURE

SUBJECT: INFORMATION ON COMPONENT AND SERVICE PROCEDURE CHANGES

MODELS: 1996 CADILLAC CONCOURS, DEVILLE, ELDORADO, SEVILLE 1996 OLDSMOBILE AURORA WITH 4.6L AND 4.0L ENGINES (VINS 9, Y, C-RPOS L37, LD8, L47)

THE FOLLOWING INFORMATION REFLECTS COMPONENT CHANGES FROM THE 1995 TO 1996 MODEL YEAR 4.6L NORTHSTAR (RPOS L37, LD8) AND 4.0L AURORA V8 (RPO L47) ENGINES. UNLESS SPECIFIED OTHERWISE, THESE PROCEDURES AND COMPONENT CHANGES APPLY ONLY TO 1996 MODEL YEAR ENGINES.

PISTONS--REDUCED TOP RING LAND HEIGHT

THE TOP RING LAND HEIGHT ON ALL PISTONS IS REDUCED FROM 6.0 MM TO 4.5 MM (FIGURE 1). DO NOT USE PISTONS WITH A 4.5 MM TOP RING LAND HEIGHT IN A 1993-95 4.6L OR 4.0L ENGINE.

NITRIDED STEEL TOP PISTON RING

ALL COMPRESSION (TOP) RINGS ARE NOW COMPOSED OF NITRIDED STEEL INSTEAD OF THE PREVIOUS MODEL YEAR MOLYBDENUM OR "MOLY" STEEL. WHEN SERVICING THE PISTON RINGS OF A 1996 4.6L OR 4.0L ENGINE YOU MUST USE A PISTON RING EXPANDER TO REMOVE OR INSTALL THE PISTON RINGS. THE RINGS SHOULD BE EXPANDED JUST ENOUGH TO SLIP THE RING AROUND THE TOP OF THE PISTON TO AVOID SHATTERING THE RING.

THE TOP RING WIDTH HAS BEEN REDUCED TO 1.2 MM FROM 1.5 MM. THE PRIOR MODEL YEAR PISTON RING (1.5 MM) WILL NOT FIT ON THE 1996 PISTON. DO NOT USE THE 1996 RING ON THE PRIOR MODEL YEAR PISTONS. PROPER COMBUSTION SEALING CANNOT BE OBTAINED IF THE 1.2 MM PISTON RING IS USED ON A PISTON DESIGNED FOR 1.5 MM PISTON RINGS (6.0 MM TOP RING LAND HEIGHT).

CRANKSHAFT--SMALLER DIAMETER BALANCER BOLT

A SMALLER DIAMETER (M14) CRANKSHAFT BALANCER BOLT REPLACES THE LARGER (M18) BOLT USED IN PRIOR MODEL YEAR ENGINES. THE NEW BOLT HAS A REVISED TORQUE SPECIFICATION OF 50 N.M PLUS 120 DEGREES (37 LBS FT PLUS 120 DEGREES) VERSUS THE PRIOR YEAR 60 N.M PLUS 120 DEGREES (44 LBS FT PLUS 120 DEGREES) SPECIFICATION.

NOTICE: A SMALL NUMBER OF 1996 4.0L ENGINES WERE BUILT WITH THE 1995 CRANKSHAFT (LARGER BOLT). BE SURE TO IDENTIFY THE SIZE OF THE BOLT TO DETERMINE PROPER TORQUE SPECIFICATION WHEN INSTALLATION IS NECESSARY.

THE SMALLER BOLT IS NOT A MANDATORY UPGRADE AND SHOULD ONLY BE USED WHEN A REPLACEMENT CRANKSHAFT REQUIRES IT. CRANKSHAFTS WITH THE M14 BALANCER BOLT MUST ONLY BE USED ON 1994-96 MODEL YEAR 4.6L AND 4.0L ENGINES. 1993 4.6L ENGINES CONTAIN FORGED STEEL CONNECTING RODS WHICH REQUIRE A 1993 MODEL YEAR SPECIFIC CRANKSHAFT.

MAIN BEARING BOLTS/OIL SCRAPER

THE OIL SCRAPER (FIGURE 2, NUMBER 2) IS NOW ATTACHED BY THE INBOARD NUMBER 1 AND OUTBOARD NUMBER 3 MAIN BEARING BOLTS INSTEAD OF THE STUD/NUT ARRANGEMENT USED ON PREVIOUS MODEL YEARS. ONE STUD HEADED MAIN BEARING BOLT (NUMBER 4) REMAINS FOR RETENTION OF THE OIL SUMP PICKUP.

ELIMINATION OF OIL SUMP O-RING (FIGURE 3)

THE BLACK O-RING USED TO SEAL THE OIL SUMP PICKUP (NUMBER 3) HAS BEEN REPLACED WITH A SILICONE SEAL INTEGRAL TO THE OIL MANIFOLD PLATE (NUMBER 1). WHEN INSTALLING THE SUMP PICKUP, COAT INTEGRAL SEAL WITH CLEAN ENGINE OIL BEFORE INSERTING THE TUBE. THE PICKUP TUBE IS STILL HELD IN PLACE WITH A BOLT (NUMBER 2) AND NUT (NUMBER 4) LIKE PREVIOUS MODEL YEARS.

KNOCK SENSOR RELOCATION (FIGURE 4)

THE KNOCK SENSOR IS RELOCATED FROM THE SIDE OF THE ENGINE BLOCK TO THE VALLEY BETWEEN THE CYLINDER BANKS. THE WIRE LEAD AND CONNECTOR (NUMBER 1) FOR THE KNOCK SENSOR IS LOCATED IN THE STARTER MOTOR HARNESS. TO SERVICE THE KNOCK SENSOR AND OR CONNECTOR IT IS NOW NECESSARY TO REMOVE THE INTAKE MANIFOLD. REFER TO SECTION 6A2 - ENGINE MECHANICAL FOR PROPER INTAKE MANIFOLD REMOVAL PROCEDURES.

EXHAUST SYSTEM - FLEX COUPLING (FIGURES 5 AND 6)

ALONG WITH NEW DUAL WALL EXHAUST MANIFOLDS AND THE ADDITION OF TWO OXYGEN SENSORS, POSITIONED DIRECTLY UP- AND DOWNSTREAM OF THE CATALYTIC CONVERTER, THE EXHAUST SYSTEM NOW CONTAINS A FLEX-JOINT COUPLING. THE COUPLING (NUMBER 1) IS INTEGRATED INTO THE "Y-PIPE" AND IS CONNECTED TO THE REMAINDER OF THE EXHAUST SYSTEM WITH A FLAT JOINT FACE (NUMBER 2) HELD BY FOUR BOLTS. THE EXHAUST SYSTEM MUST NOT BE ALLOWED TO HANG IN SUCH A MANNER THAT THE WEIGHT OF THE SYSTEM IS SUPPORTED AT THE FLEX COUPLING. IF THIS OCCURS, A NOISE CONDITION MAY RESULT.

REFER TO THE 1996 SECTION 6A2-ENGINE MECHANICAL SERVICE MANUAL FOR PROPER SERVICE PROCEDURES OF THE COMPONENTS CONTAINED IN THIS BULLETIN.

FIGURES: 6 ATTACHMENTS: 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.

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