Engine - Thump or Knock Noise At or Just Off Idle

9227oldsmobile01

NUMBER: 92-T-67

CORP.REF.NO: 206002

DATE: March 1992

SECTION: 6A


SUBJECT:
THUMP OR KNOCK NOISE AT OR JUST OFF
IDLE,- INSTALL NEW SINGLE BELT ACCESSORY DRIVE BELT (S.B.A.D)

MODELS/YEARS:
1992 ACHIEVA, CUTLASS CIERA/CRUISER,
EIGHTY EIGHT, NINETY EIGHT,
TORONADO/TROFEO, SILHOUETTE


New S.B.A.D. belts were released for production October 1, 1991 and are now available for service on 1992 3300/3800 (VIN N, L, 1) engines. These new belts, with smoother grooves, greatly reduce "belt pilling". Belt pilling is a condition in which particles of belt material forms small balls or "pills" in the belt grooves. Some degree of pilling is normal, however, excessive pilling can cause a thump or knock noise when the pills pass over various pulleys. The thump or knock noise could be misdiagnosed as an engine or accessory noise.

The following checklist will help diagnose and repair a belt pilling condition:

1 . Remove the belt and momentarily run the engine to confirm that the source of the noise has disappeared.
2a. If the noise does not disappear, there are other factors that can cause a thump or knock noise. See
Section 6 in the service manual for additional diagnostic information.
2b. If the noise does disappear; inspect the power steering pulley for proper alignment and repair as
necessary.
3. Inspect all pulleys for excess paint, debris or pills in the grooves - clean as necessary.
4. Install a new belt from the listed service parts.


MODEL PART NUMBER
Eighty Eight, Ninety Eight, 24502137
Toronado/Trofeo, Silhouefte

Cutlass Ciera/Cruiser 24502138

Achieva 24502139

Note:
Supercharged 3800 V6 engines were all produced with new smoother groove belts. The part numbers for these belts are:

Supercharger Drive 24501446
Alternator Drive 24501447

Parts are currently available from GMSPO.