ENGINE HARMONIC BALANCER REDESIGN (NEW P/N RELEASED)

SUBJECT: ENGINE HARMONIC BALANCER REDESIGN

MODELS: ALL 1973-1988 6.0/7.OL GASOLINE ENGINE POWERED MEDIUM DUTY VEHICLES

Effective with the engine manufacturing dates listed below, all 6.0/7.OL gasoline engines are manufactured with a new engine harmonic balancer. The new balancer uses a bonding agent on both sides of the rubber elastomer isolator, eliminating outer inertia ring spinning, or "walking" out of position. The physical appearance of the balancer remains unchanged, however, a "B" is stamped behind the balancer date build code which appears on the face of the inertia ring.

Earlier production vehicles can be retrofitted by installing the following service parts available through GMSPO:

ENGINE MODEL NEW PART NUMBER ------------ --------------- 1973-88 6.OL (366 CID) 10106421

1973-88 7.OL (427 CID) 10106422

EFFECTIVE ENGINE PRODUCTION DATE ENGINE BUILD CODE ---------------- ----------------- 6.0L (366 CID) - T 1221 XXX December 21, 1987

7.0L (427 CID) - T 0301 XXX March 1, 1988

HARMONIC BALANCER DATE BUILD CODE (TYPICAL)

A 8 S B Month Year Simson Bonded Built Built (Supplier) A = January

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.