Engine - Diagnosing Noise & New Harmonic Balancer
Bulletin 85-6-29Date Apr. '86
Ref. No. 85-323-6
SUBJECT: DIAGNOSING ENGINE NOISES
MODELS AFFECTED: 1985 CENTURYS & ELECTRAS EQUIPPED WITH 3.8L MFI (VIN CODE 3) ENGINES
The following may prove helpful in resolving a particular engine noise condition on the above engines. The noise we refer to, sometimes called "mystery noise", is the result of fore and aft movement of the rod on the crank pin journal.
The noise is normally heard when engine RPM is just above idle, it's thoroughly warmed up, and under light load (car in gear). The noise can best be described as a light ticking sound much like overhead noise, but appears to come from the bottom part of the engine, and is most pronounced at the rear of the front wheel opening, right side. Removal of the crankshaft balancer and belts will usually greatly reduce the noise level.
A new crankshaft balancer which eliminates this noise, through dampening, is available from GMWDD, under part number 25527065.