Engine - Knock Diagnostic Procedures

9224BUICK01

Bulletin 89-6-19

Date Sept. '89

Ref. No. 89-230-6

Corp. Ref. No. 936119R


SUBJECT:
ENGINE KNOCK DIAGNOSIS (NOISES)


MODELS AFFECTED:
1988-89 CENTURYS WITH 2.5L ENGINE (VIN CODE R) AND
1988-89 SKYLARKS WITH 2.5L ENGINE (VIN CODE U)
WITH AUTOMATIC TRANSMISSIONS


Customer comments may be received regarding engine knock or rattle noises on the following vehicles:

1988-89 Skylarks with 2.5L engine (VIN Code U)
1988-89 Centurys with 2.5L engine (VIN Code R)

Usually, this noise is evident only on vehicles equipped with automatic transmissions. This bulletin provides guidelines which may be used to distinguish between camshaft timing gear knock/rattle noise and force balancer gear knock/rattle noise. These noises sound very similar to one another under certain operating conditions and isolating the source may be difficult.





The chart illustrates the engine and transmission operating conditions at which force balancer gear or the camshaft timing gear knock/rattle noise is noticeable.


In order determine which system is causing the noise, shift the transmission into gear - if the knock/rattle noise becomes evident, the noise is most likely force balancer related.

IMPORTANT:
If this is the case, replacement of the force balancer and/or crankshaft will not correct the condition.

The knock/rattle condition is caused by the particular way that the teeth of the large crankshaft gear and the small balancer intermediate gear mesh together. This noise will produce no detrimental effects to the engine.

If the knock/rattle noise is not force balancer related, further diagnosis per the Service Manual is recommended to correct the condition..