Engine - Premature Main Bearing Failure

File In Section: 6 - Engine

Bulletin No.: 87-61-22

Date: March, 1998

INFORMATION

Subject:
Premature Main Bearing Failure

Models:
1996-98 Chevrolet and GMC C/K, M/L, S/T, G, P Models
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.