Diesel - Rapping or Knocking Noise

Number 84-6 (Diesel)-4 Date 2/84

Subject: RAPPING OR KNOCKING NOISE - 1982-84 DIESEL ENGINES

The 1982-84 V-8 and V-6 diesel engines have the piston pin moved .045 inches off center of the piston. This change was made to reduce the noise level of the engine. If this offset is on the wrong side, a 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 the illustration. 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 the illustration. A correctly machined piston will have an even amount of chamfer in the pin boss area as shown in the illustration.