Engine - Diagnosing Knock Noise In Front Of Engine
Group Ref.: 6 - EngineBulletin No.: 306001
Date: June, 1994
SUBJECT:
KNOCK NOISE IN FRONT OF ENGINE
(PROCEDURE TO DIAGNOSE AND REPAIR)
MODELS:
1992-93 BUICK CENTURY AND SKYLARK
1992-93 OLDSMOBILE ACHIEVA, CUTLASS CIERA, CUTLASS CRUISER
1992-93 PONTIAC GRAND AM WITH 3300 ENGINE (VIN N - RPO LG7)
1992-94 BUICK LESABRE, PARK AVENUE, REGAL AND RIVIERA
1992-94 CHEVROLET LUMINA APV
1992 OLDSMOBILE TORONADO
1992-94 OLDSMOBILE EIGHTY EIGHT, NINETY EIGHT AND SILHOUETTE
1992-94 PONTIAC BONNEVILLE AND TRANS SPORT WITH 3800/3800SC ENGINE (VINS L, 1 - RPOs L27, L67)
THIS BULLETIN IS REVISED TO UPDATE THE MAIN BEARING CLEARANCE MEASUREMENT PROCEDURE (ITEM # 5), INCLUDE 1994 MODEL YEAR VEHICLES, ADD WARRANTY INFORMATION AND ARTWORK. PREVIOUS DIVISIONAL PUBLICATION NUMBERS WERE:
DIVISION BULLETIN NUMBER
BUICK 93-6-12
CHEVROLET 93-165-6
GM CANADA 93-6-113
OLDSMOBILE 93-T-59
PONTIAC 93-6-34
Some owners may comment of a knocking noise in the engine.
To aid in diagnosis and repair of a knock noise at the front of a 3300/3800/3800SC engine, the following procedure should be followed:
1. With the accessory drive belt installed, run the engine until operating temperature is reached and verify that the knock noise is present.
2. With the engine running, slightly unload the tension on the accessory drive belt by lifting the belt tensioner with the appropriate wrench. Continue to lift the tensioner until the belt begins to slip or squeal. Extreme care should be used around the drive belt with the engine running. If the noise is still present, then the cause is most likely accessory belt "pilling" or power steering pump surge. Proceed to step 3. If the noise is not present with the tension relieved, then the noise is most likely main bearing knock due to excessive number 1 bearing clearance. Proceed to Step 5, "Main bearing clearance checks and repairs."
3. Remove accessory drive belt (examine belt and all pulleys for pilling) replace belt, part number 24502762 for NB, 24502761 AB, 10230725 for 3800 L27, and 24503513 and 24503564 for 3800SC (L67). Refer to Corporation Reference Number 206002R (Chevrolet 92-284-6; Pontiac 92-6-31A; Oldsmobile 92-T-67; Buick 92-6-7A; GM of Canada 92-6-111) and clean pulleys, run engine until operating temperature is reached and verify that the knock noise is present. If the noise is still present, then the cause is most likely power steering pump surge. Proceed to step 4.
4. Power steering pump surge problems have been found mainly on "N" body vehicles, but should be considered on all other 3300/3800 equipped vehicles exhibiting these knock noise problems. Eliminate the steering gear from the power steering system by routing the inlet (pressure) hose back into the return hose therefore bypassing the gear, run engine and verify that the knock is present. If the noise is still present, then proceed to main bearing clearance checks and repairs. If the noise is not present, then verify inlet and outlet hose flow (no overcrimp or blockage) and routing (no groundout). If the inlet and outlet hose flow is verified, then replace the pump.
5. "On-Vehicle" Number 1 Main Bearing Clearance Measurement Procedure
- Remove accessory drive belt.
- Drain engine oil and remove the engine oil pan.
- Remove the number 1 main bearing cap as follows:
- Loosen main bolts with hand tools
- Completely back out both main bolts
- Insert the main bolts half way into the main cap
- Use one hand to squeeze the bolts toward each other
- With a small hammer in the other hand, tap the hex of the bolts sideways and downward until the main cap is free from the cylinder block.
- Position an adjustable support stand underneath the harmonic balancer. A short length of 2 x 4 wood placed between the harmonic balancer and the support stand will prevent damage to the harmonic balancer.
- Adjust the support stand to push the crankshaft upward until the crank journals are solidly seated against the upper main bearing halves.
- Place a piece of gauging plastic across the entire width of the lower bearing in the removed main cap. The gauging plastic should be placed in the center of the bearing (6 O'Clock position when viewed with main cap in place).
- Reinstall the main cap and tension the main bolts to published specifications. DO NOT use power tools to tighten the main bolts.
- Remove the main cap as outlined above.
- Measure the flattened gauging plastic at its widest point with the scale printed on the gauging plastic package.
- The clearance should be 0.0008 - 0.0022 inch (0.020 - 0.056 mm).
- If the original clearance is 0.0012 inch (0.030 mm) or less, the main bearing is probably not the source of the knock.
- If the clearance is between 0.0018-0.0022 inch (0.046 - 0.056 mm), install a complete 0.001 inch undersize main bearing insert kit, P/N 12350094.
NOTE:
Remove the crankshaft support stand to allow clearance to remove the upper bearing half. To remove an upper main bearing, use a roll-out pin, which can be obtained locally or through Kent-Moore, P/N J-8080. A roll-out pin fits in the crankshaft drilled oil hole while its angled head lies flat against the edge of the bearing. When the crankshaft is turned, the roll-out pin removes the bearing without causing damage. The pin can also be used to Install the new bearing.
- If the clearance is greater than 0.0012 inch (0.030 mm) and less than 0.0018 inch (0.046 mm), install the lower half only of a 0.001 inch undersize main bearing insert kit, P/N 12350094.
- Perform a final main bearing clearance check, following the above procedures. The resulting clearance of the number 1 main bearing SHOULD NOT be less than 0.0008 inch (0.020 mm).
- Install the engine oil pan using a new gasket, P/N 12350249. Tension the oil pan bolts to published specifications using a torque wrench.
NOTE:
Over tightening oil pan bolts causes the crush limiters on the oil pan mounting surface to collapse. When the crush limiters are collapsed, the oil pan gasket will be over compressed and will split. An oil leak at the pan rail will result. DO NOT use any sealers on the pan gasket; install the gasket dry.
- Remove the crankshaft support stand.
- Install the accessory drive belt.
- Fill the engine with oil.
PARTS INFORMATION:
Parts are currently available from GMSPO.
WARRANTY INFORMATION:
