RAPPING OR KNOCKING NOISE PISTON PIN OFFSET LOCATION

VEHICLES AFFECTED: 1982-84 Vehicles Equipped With 5.7 or 4.3L Diesel Engines

The 1982-84 V-8 and V-6 diesel engines have the piston pin moved .045 inches off centre of the piston. This change was made to reduce the noise level of the engine. If this offset is on the wrong side, & rapping or knocking noise will be heard as the engine warms up. It is possible to locate the cylinder by loosening fuel lines to the nozzles. The noise level will be reduced.

There are two ways that the piston offset could be on the wrong side:

1. The piston could be installed backwards.

2. The piston could be mis-machined.

To determine which of the above two conditions may have occurred, refer to Fig. 1. The cast notch in the top of the piston should be toward the front of the engine. If the cast notch is properly located, then the piston should be removed from the engine and inspected. If the piston is incorrectly machined, it will have an uneven chamfer as shown in Fig. 2.

A correctly machined piston will have an even amount of chamfer in the pin boss area as shown in Fig. 3.

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.