REAR MAIN OIL LEAK DIAGNOSE / INSPECT CRANKSHAFT

VEHICLES AFFECTED: 1987 R/V, G, M AND 1988 C/K MODELS EQUIPPED WITH 4.3L (VIN CODE Z) ENGINES

*THIS BULLETIN CANCELS AND SUPERCEDES SERVICE BULLETIN 88-643-1001 ALL COPIES OF WHICH SHOULD BE DESTROYED.

Some 1987 R/V, G, M and 1988 C/K trucks equipped with 4.3L engines with engine build date codes prior to T1202 may experience a rear main oil seal leak condition due to a poor surface finish on the crankshaft sealing surface.

NOTE: Engine date code location is shown in Figure 1. The build date codes may be found in this area and appear as shown in the following example:

T1202ABC

The first letter indicates the plant where the engine was manufactured the next four numbers indicate the day of manufacture; in this case 12 month 2nd day, and the last three digits may be any broadcast code. To diagnose this condition check the oil leak using an ultraviolet light and engine oil dye. If ALL of the following conditions are met replace the crankshaft and rear main oil seal.

1. Leakage is between the crankshaft sealing surface and crankshaft oil seal lip.

2. Engine build code is prior to T1202. (See explanation above).

3. Removal and inspection of the rear rear main oil seal indicates the seal is not torn.

If all of the above conditions are not met, replace only the rear main oil seal and retainer.

NOTICE: THE ASSEMBLY OF THE REAR MAIN OIL SEAL AND RETAINER MUST BE PERFORMED IN THE FOLLOWING SEQUENCE OR POTENTIAL FOR AN OIL LEAK AT THE REAR MAIN OIL SEAL EXISTS.

1. LOOSEN OIL PAN FASTENERS AND ALLOW OIL PAN AND OIL PAN GASKET TO FALL FREE OF REAR MAIN OIL SEAL RETAINER.

2. INSTALL NEW REAR MAIN OIL SEAL AND RETAINER. TORQUE RETAINER FASTENERS TO SPECIFICATION.

3. AFTER TORQUING RETAINER FASTENERS, TORQUE OIL PAN FASTENERS TO SPECIFICATION.

IF THIS PROCEDURE IS NOT FOLLOWED THE OIL PAN MAY INTERFERE WITH THE RETAINER AND NOT ALLOW THE REAR MAIN OIL SEAL TO CENTER ON THE CRANKSHAFT.

This condition was corrected in production effective with the following VIN breakpoints:

1987

Flint GMC HF712338 Chevrolet HF345461

Janesville GMC HJ515177 Chevrolet HJ138800

Baltimore GMC HB512872 Chevrolet HB150460

St. Louis GMC HS515759 Chevrolet HS144963

Lordstown GMC H7512809 Chevrolet H7138970

Scarborough GMC H4507505 Chevrolet H4114959

1988

Fort Wayne GMC Z500019 Chevrolet Z100022

Pontiac GMC JE500221 Chevrolet JE100451

Oshawa GMC SOP Chevrolet SOP

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.