Engine - Cold Knock, Replace Oil Filter/Bearings/PROM
File In Section: 6 - EngineBulletin No.: 37-61-05A
Date: October, 1995
Subject:
Cold Engine Knock (Replace Oil Filter/Bearings/PROM)
Models:
1990-95 Chevrolet and GMC Truck C/K, R/V, S/T, M/L, G, P Models
1991-92 Oldsmobile Bravada
with 4.3L (VIN Z - RPO LB4), 5.7L (VIN K - RPO L05),
7.4 (VIN N - RPO L19) Engine
This bulletin is being revised to add the 1995 model year information. Please discard Corporate Bulletin Number 37-61-05 (Section 6 - Engine).
Condition
Some late model truck engines have been reported to exhibit "cold knock" on start up. "Cold Knock" usually occurs after the vehicle has been completely warmed up, then parked for 8 or more hours in ambient temperatures of 35° F or less. "Cold knock" can be separated into three distinct categories.
1. Short Duration - Harsh, deep metallic knock that usually lasts from 1 to 10 seconds. Generally classified as a bearing or rod knock.
2. Valve Train - Light clatter, tick or click that may last up to 1 minute.
3. Piston Slap - Metallic knock that occurs only under load. Piston slap may last as long as 5 minutes.
Correction
Category A: Short Duration Knock
This matrix describes the repair for each affected model year and engine.
Specific information for each affected model year and engine is supplied.
1992 LB4 VIN Z with "cold knock" only
1992-93 LB4 VIN Z with "cold knock" and installed field fix PROM OR with "cold knock" and detonation
1990-95 LB4 VIN Z
Install check valve oil filter P/N 12555891 (FRAM PH3980). If the filter does not cure the condition, install the appropriate calibration from the tables (calibrations are available for all 1992 and some 1993 LB4 applications). If a calibration is not offered or does not cure the short duration cold knock condition, install the appropriate main bearings as determined by the following procedure.
Calibration Information - 1992-93 LB4 VIN Z
The revised PROMs reduce spark advance after the engine is started. The reduction in spark lowers the cylinder pressure and eliminates the knock. The revised PROMs will NOT eliminate a piston slap (Category C) or valve train noise (Category B) concern. The base cold knock PROM contains the previously released calibration updates. For 1992 LB4, the previous field release is included for torque converter clutch (TCC) lock up (see Bulletin 137107 - Chevrolet 92-75-7A; GMC Truck 92-7A-40; Oldsmobile 92-T-34; Canada 9274L60100) for automatic transmissions, or neutral gear rattle for manual transmissions (see Bulletin 267201R - Chevrolet 92-187B-7B; GMC Truck 92-7B-149A; Canada 93-7B-105). If a vehicle has had a detonation fix PROM installed previously, select the combined detonation and cold knock fix PROM for the application. See Bulletin 376508 for more information on field fix PROM for the application and detonation.
Important:
Use of a detonation fix PROM in a non-detonating vehicle may result in degraded driveability.
GMSPO currently stocks three (3) PROMs for each light duty 1992 model year LB4 application.
Base
Cold Knock Fix
Combination Cold Knock and Detonation Fix
GMSPO Service Parts Assistance Center (SPAC 1-800-433-6961) will have information available on each PROM part number. Select the PROM from the table. Old Broadcast Code (Old B/C Code) and Scan I.D. information has been supplied to help installed previously. Use a TECH-1 to determine the Scan I.D. of the PROM in the vehicle or remove the PROM and read the Broadcast Code (B/C Code). If the B/C Code/Scan I.D. can be found in the first table, a detonation fix has not been installed.
PROMs are currently available GMSPO.
1990-95 L05 VIN K
1993 to 1995 L05 VIN K
Install the appropriate check valve oil filter P/N 25160561 (PF1218 for two-wheel C-series and P/N 12555891 (FRAM PH3980) for four-wheel drive K-series). If the oil filter does not cure the condition, install the appropriate calibration from the table (calibrations are available for some 1993 and 1994 L05 applications). All calibrations are for light duty vehicles equipped with 4L60-E (M30) transmissions (no heavy duty emission/4L80-E calibrations are available). If a calibration is not offered or does not cure the short duration cold knock condition, install the appropriate main bearings as determined by the procedure.
1990-94 L19 VIN N
Install a check valve oil filter; no other recommended actions at this time.
Important:
The previous actions are only applicable to short duration cold knock. These actions will not eliminate a knock occurring under load or a knock lasting for more than 10 seconds.
Two main bearing procedures are recommended:
1. For main bearing replacement with the engine IN the vehicle: C, G, P, M and L vehicles
2. For main bearing replacement with the engine OUT OF the vehicle: K, S and T
THE FOLLOWING PROCEDURE IS TO BE USED FOR VEHICLES REQUIRING MAIN BEARING REPLACEMENT WITH THE ENGINE IN THE VEHICLE
Recommended for C, G, P, M and L vehicles.
Important:
A OEM training video has been produced for in-vehicle main bearing replacement procedure. One copy of the video will be sent to each dealer. If the video has not been received, contact XPRESS 1 Distribution Center at 1-800-783-3034.
Main Bearing Clearance Determination and Installation Procedure
1. REMOVE THE SERPENTINE BELT, dipstick, dipstick tube and disconnect the negative battery cable.
2. Raise the vehicle and remove (or set aside) any parts restricting access to the oil pan bolts (i.e., starter motor, oil cooler lines, oil filter adapter, flywheel inspection cover).
3. Remove the oil pan, oil pump, and shield.
4. Remove # 5 (flange) bearing cap. Wipe the oil from the crankshaft journal and the lower main bearing insert.
5. Place a screw jack under an accessible part of the crankshaft, carefully apply pressure to the crankshaft to force it solidly against the top bearing insert. The reason for this is to remove any clearance between the top bearing insert and the crankshaft. If this step is not performed, a smaller than actual clearance will be measured.
Important:
This should be done as close as possible to the bearing being measured. This step is only required for on-vehicle service where the engine cannot be turned upside down as on an engine stand.
6. Place a piece of plastigage across the width of the lower bearing insert (parallel to the centerline of the crankshaft).
7. Reinstall # 5 main bearing cap. Torque to 110 N.m (80 lb ft). Do not allow crankshaft to turn.
8. Carefully remove the # 5 main bearing cap and bearing insert. The flattened plastigage will adhere to either the bearing insert or the crank journal. Do not remove the plastigage from the insert or journal.
9. On the edge of the plastigage envelope, there is a graduated scale. Without removing the flattened plastigage, measure its width at the widest point using the graduated scale on the plastigage envelope.
10. The desired main bearing clearance is 0.0008" - 0.0028". If the clearance measured with the plastigage is greater than 0.0028", write down the clearance. Next, read the back of the bearing insert to determine what size bearing was originally installed (usual STD, 0.0006", 0.0010" or 0.0012"). The size stamped on the bearing is the effective undersize when both inserts are installed. For example, a 0.0006" undersize bearing set consists of two (2) 0.0003" thicker bearing inserts, both stamped 0.0006".
11. Remove the top bearing insert using tool J 8080 and read the back to determine what size upper bearing insert was originally installed. The top insert may be different size than the bottom.
12. Calculate the original bearing undersize by dividing the size on each insert by 2, then add the values together.
EXAMPLE 1:
The lower insert is stamped 0.0006" and the upper is stamped 0.0010". Divide 0.0006" by two to get 0.0003". Divide 0.0010" by 2 to get 0.0005". Add 0.0003" and 0.0005" together to calculate the bearing undersize, which is 0.0008" in this case.
EXAMPLE 2:
The lower insert is stamped STD (standard) and the upper is stamped 0.0010". The undersize for a STD bearing is 0. Divide 0 by 2 to get 0. Divide 0.0010" by 2 to get 0.0005". Add 0 and 0.0005" together to calculate the bearing undersize, which is 0.0005" in this case.
13. Add the original bearing undersize calculated in step 12 to the clearance measured and written down in step 9. For example, if a clearance of 0.0030" was measured with plastigage in step 9 and the calculated bearing undersize from step 12 was 0.0005", the bearing clearance for that particular main journal is equal to 0.0030" plus 0.0005". The bearing clearance would be 0.0035" in this case.
14. Determine which of the combinations of two sizes of replacement bearings will produce the desired clearance. The two sizes available are 0.001" and 0.002". One insert of each size may be combined to produce an intermediate undersize of 0.0015". Subtract the replacement bearing size from the actual clearance to determine which bearing should be used. The bearing that should be used is the one which gives a clearance closer to 0.0008" than to 0.0028". The clearance must not be less than 0.0008". Using the example from step 11, the actual clearance is 0.0035". Subtracting 0.001" from 0.0035" will give a clearance of 0.0025", just barely within the required range. Subtracting 0.002" from 0.0035" will give a clearance of 0.0015". The 0.002" undersize bearing set would be the one to use in this case since it gives a clearance closer to 0.0008", but not less.
15. Install the replacement upper main bearing insert using tool J 8080.
16. Install the replacement lower main bearing insert in the main bearing cap. Lay a piece of plastigage across the width of the lower main bearing insert (same as step 5).
17. Repeat steps 7, 8 and 9.
18. Measuring the plastigage with the scale on the envelope, verify the clearance of the replacement bearings is within the range of 0.001" to 0.003".
19. Repeat steps 4 through 16 for each main bearing.
20. Thrust the crankshaft forward and backward several times to seat the thrust bearing.
21. Reinstall oil pump; torque to 88 N.m (65 lb ft).
22. Reinstall the oil pan and other hardware.
23. Before starting the engine, remove the fuel pump fuse and crank the engine until oil pressure registers on the gauge. Stop cranking, let the starter cool down, then crank for another 15 seconds.
24. Install fuel pump fuse, start engine, check for leaks or unusual noises.
25. Road test vehicle, check for leaks or unusual noises.
THE FOLLOWING PROCEDURE IS TO BE USED FOR VEHICLES REQUIRING MAIN BEARING REPLACEMENT WITH THE ENGINE OUT OF THE VEHICLE
Recommended for K, S and T vehicles.
1. Remove the engine from the vehicle using the appropriate service manual procedure.
2. Mount the engine on an engine stand, flip the engine so the oil pan is facing up.
3. Remove the oil pan.
4. Remove the oil pump and shield.
5. Remove the dipstick tube.
6. Remove one (1) main bearing cap (must do one at a time).
7. Plasti-gage bearing.
8. If the bearing clearance is out of specification (clearance greater than 0.003 inches), remove upper main bearing from the block.
9. Check the size of the original bearing.
10. Determine what combination of new bearings are required to get the clearance in the acceptable range of 0.0008 inches to 0.0028 inches. See steps 12 through 14 in the "in-vehicle" service outlined above.
11. Reinstall the upper main bearing.
12. Reinstall the main cap and lower bearing; torque to 110 N.m (80 lb ft).
13. Repeat for each main bearing.
14. Reinstall oil pump and shield; torque to 88 N.m (65 lb ft).
15. Reinstall dipstick tube.
16. Reinstall oil pan.
17. Reinstall engine in vehicle.
18. Before starting the engine, remove the fuel pump fuse and crank the engine until oil pressure registers on the gauge. Stop cranking, let the starter cool down, then crank for another 15 seconds.
19. Install fuel pump fuse, start engine, check for leaks or unusual noises.
20. Road test vehicle, check for leaks or unusual noises.
Correction
Category B: Valve Train Clatter, Tick or Click
For 1992-94 vehicles equipped with a 4.3L V6 (LB4 VIN Z or L35 VIN W) engine see Corporate Bulletin 376006 for information on converting from net lash to adjustable lash and/or re-lashing the valves on an adjustable lash system.
Investigation of "cold knock" is continuing. Updates will continue to be provided when available.
Parts Information
Check-Valve Filters Description Part Number
V6, V8 (Four-Wheel Drive) FRAM PH3980 12555891
V8 (Two-Wheel Drive), Mark V8 PF1218 25160561
The FRAM PH3980 is to be used in place of the
PF52. The PH3980 provides superior anti-drainback
performance, a key factor in reducing cold knock.
FRAM filters are to be procured locally until
08-15-95. After this date the filters may be ordered
from GMSPO using the supplied part number. Orders
placed to GMSPO prior to this date will not be
placed on backorder.
Bearings Description Part Number
0.001" Main Bearing Kit, Positions 1-4 on V8, 1-3 on V6 10120992
0.001" Main Bearing Kit, Flange # 5 on V8, # 4 on V6 10120994
0.002" Main Bearing Kit, Positions 1-4 on V8, 1-3 on V6 12329758
0.002" Main Bearing Kit, Flange # 5 on V8, # 4 on V6 12329792
Main bearing kits are currently available from GMSPO.
All calibrations are currently available from GMSPO.
Warranty Information