Engine - Metallic Knock Sound
File In Section: 6 - EngineBulletin No.: 47-61-42
Date: February, 1995
Subject:
Metallic Knock Sound from Engine (Diagnose/install New Piston Wrist Pin)
Models:
1993 Cadillac Allante
1993-94 Cadillac Eldorado, Seville
with 4.6L Northstar Engine ("VINs 9, V - RPOs L37, LD8)
CONDITION
Some owners may comment on an engine noise described as a hydraulic valve lifter tick. This noise may be heard at engine idle with engine speed less than 1000 rpm.
CAUSE
This noise may be caused by a damaged piston wrist pin or excessive clearances between the piston, piston wrist pin, and connecting rod which may result in engine failure. All 1993 and some early 1994 model year 4.6L Northstar engines were equipped with piston wrist pins containing a formed step at the center of the pin. A new piston wrist pin with constant (straight) wall thickness was introduced during the 1994 model year replacing the formed step design (Figure 1 and 2).
CORRECTION
Perform the following step BEFORE removing the engine assembly from the vehicle:
Using a stethoscope, idle the engine and isolate the piston where the knocking sound is most evident. AFTER removing the engine, intake manifold, cylinder heads and lower crankcase assembly:
1. Inspect the suspect piston and wrist pin for damage. If the piston wrist pin is damaged, the piston, rings, wrist pin, connecting rod, connecting rod bearings and bolts must be replaced.
2. Install the new piston wrist pin with a constant (straight) wall thickness. To ensure proper engine balance is maintained, replace the remaining formed step design wrist pins.
3. If the piston wrist pin is not damaged, inspect the connecting rod to piston wrist pin clearance (0.002 mm to 0.022 mm) and the piston to wrist pin clearance (0.002 mm to 0.013 mm). If the clearance between these components is out of specification (refer to Section 6A2 of the Service Information Manual), replace as necessary.
1993 model year 4.6L Northstar engines are equipped with forged connecting rods. The connecting rod bolts may be reused in 1993 engine with forged rods.
1994 model year 4.6L Northstar engines are equipped with powdered metal rods which use rod bolts designed to yield when torqued to specification Thus, the bolts must be replaced in a 1994 4.6L engine whenever a rod cap is removed.
Connecting rods must not be interchanged between 1993 and 1994 model year engines due to crankshafts used specifically with each type of connecting rod. If the connecting rods are interchanged, the engine will be out of balance.
Important:
Never reuse connecting rod bearings with run time. Whenever a rod cap is removed, always replace the bearings and perform a clearance check with plastic gauge. Refer to Section 6A2 of the Service Information Manual for the plastic gauge procedure.
Whenever servicing the connecting rod and/or main bearings in any 4.6L engine, apply a coat (completely cover) of Lubrizol, P/N 9780631, (Canada P/N 992869) to the bearing surfaces and crankshaft journals.
We believe this source and their product to be reliable. There may be additional manufacturers of such products. General Motors does not endorse, indicate any preference for or assume any responsibility for the products from this firm or for any such items which may be available from other sources.
Important:
Whenever the 4.6L engine has been disassembled and reassembled, the priming procedure must be performed. Refer to service bulletin number 476110 for engine priming procedures.
PARTS INFORMATION
Refer to the part numbers chart when replacing the piston wrist pin.
Parts are currently available from GMSPO.
WARRANTY INFORMATION
For vehicles repaired under warranty, use:
Labor Operation Labor Time
J13OO - for Right Bank Use published labor
J13O1 - for Left Bank operation time
J13O7 - for Both Banks