COLD ENGINE KNOCK - INSTALL CHECK VALVE OIL FILTER/CHANGE. GMC Truck Jimmy

REVISION 05/05/93

THIS BULLETIN IS BEING REVISED TO CHANGE INFORMATION IN THE CORRECTION SECTION AND TO UPDATE THE WARRANTY INFORMATION FOR GMC TRUCK ONLY.

REVISION 08/24/93

THIS BULLETIN IS BEING REVISED TO CHANGE THE CORRECTION SECTION COMPLETELY AND REMOVE P TRUCKS.

REVISION: 02/18/94

THIS BULLETIN IS BEING REVISED TO ADD THE 1990 AND 1994 MODEL YEARS, ELIMINATE SYNTHETIC OIL USE REFERENCES AND ADD BEARING INFORMATION. PREVIOUS DIVISIONAL PUBLICATION NUMBERS WERE: CHEVROLET - 93-155A-6A, GMC TRUCK - 93-6A-111, OLDSMOBILE - 92-T-178 AND GM OF CANADA - 93-6A-117.

REVISION: 11/30/94

THIS BULLETIN IS REVISED TO UPDATE PROM INFORMATION AND ENHANCE THE "CLEARANCE DETERMINATION/INSTALLATION" PROCEDURE FOR THE MAIN BEARING. PREVIOUS DIVISIONAL PUBLICATION NUMBERS WERE:

CHEVROLET 93-155A-6A GMC TRUCK 93-6A-111 OLDSMOBILE 92-T-178 GM OF CANADA 93-6A-117

REVISION: 03/24/95

THIS BULLETIN IS REVISED TO ADD THE CORRECTION--CATEGORY B SECTION, CHANGE PARTS INFORMATION AND CHANGE CLEARANCE INFORMATION. PLEASE DISCARD BULLETIN 37-61-05 (SECTION 6 - ENGINE).

REVISION: 09/21/95

THIS BULLETIN IS BEING REVISED TO ADD THE 1995 MODEL YEAR INFORMATION. PLEASE DISCARD BULLETIN 37-61-05 (SECTION 6 - ENGINE). * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

SUBJECT: COLD ENGINE KNOCK (REPLACE OIL FILTER/BEARINGS/PROM)

MODELS: 1990-95 CHEVROLET AND GMC C/K, R/V, S/T, M/L, G, AND P TRUCKS 1991-92 OLDSMOBILE BRAVADA WITH 4.3L (VIN Z - RPO LB4), 5.7L (VIN K - RPO L05), OR 7.4L (VIN N - RPO L19) 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 DEGREES FAHRENHEIT OR LESS. "COLD KNOCK" CAN BE SEPARATED INTO THREE DISTINCT CATEGORIES.

A. SHORT DURATION - HARSH, DEEP METALLIC KNOCK THAT USUALLY LASTS FROM 1 TO 10 SECONDS. GENERALLY CLASSIFIED AS A BEARING OR ROD KNOCK.

B. VALVE TRAIN - LIGHT CLATTER, TICK OR CLICK THAT MAY LAST UP TO 1 MINUTE.

C. PISTON SLAP - METALLIC KNOCK THAT OCCURS ONLY UNDER LOAD. PISTON SLAP MAY LAST AS LONG AS 5 MINUTES.

CORRECTION: - CATEGORY A: SHORT DURATION KNOCK THE FOLLOWING MATRIX DESCRIBES THE REPAIR FOR EACH AFFECTED MODEL YEAR AND ENGINE.

1990 1991 1992 1993 1994 1995 ---- ---- ---- ---- ---- ---- LB4 FILTER FILTER FILTER FILTER FILTER FILTER BEARINGS BEARINGS PROM PROM BEARINGS BEARINGS BEARINGS BEARINGS

L05 FILTER FILTER FILTER FILTER FILTER FILTER BEARINGS BEARINGS BEARINGS PROM PROM PROM BEARINGS BEARINGS BEARINGS

L19 FILTER FILTER FILTER FILTER FILTER FILTER

SPECIFIC INFORMATION FOR EACH AFFECTED MODEL YEAR AND ENGINE IS SUPPLIED BELOW.

1990-95 LB4 VIN Z

INSTALL CHECK VALVE OIL FILTER (FRAM PH3980). IF THE FILTER DOES NOT CURE THE CONDITION, INSTALL THE APPROPRIATE CALIBRATION FROM THE TABLES BELOW (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 PROCEDURE BELOW.

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.

NOTE: 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 BELOW. OLD BROADCAST CODE (OLD B/C CODE) AND SCAN I.D. INFORMATION HAS BEEN SUPPLIED TO HELP DETERMINE IF A DETONATION FIX PROM HAS BEEN 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 FROM GMSPO.

1992 LB4 VIN Z ***FOR VEHICLES WITH "COLD KNOCK" ONLY*** TRANS AXLE EMISSION SERVICE B/C SCAN OLD B/C PLATFORM RPO RPO CLASS PROM KIT CODE I.D. CODE -------- ----- ---- -------- -------- ---- ---- ------- C12/K12 MD8 ALL NA5/NA6 16198453 BJMN 8455 AULF C12/K12 MD8 ALL NB2 16198460 BJMR 8475 AULK C12 MG5 ALL NA5/NA6 16198529 BJNR 8675 BDCW OR AULH C12 MG5 ALL NB2 16198542 BJNW 8715 BDCX OR AULL C12/K12 MT8 ALL NA5/NA6+NA1 16198536 BJNT 8695 BCZP OR AULJ K12 MG5 ALL NA5/NA6+NA1 16198536 BJNT 8695 BCZP OR AZUS C12/K12 MT8 ALL NB2+NA1 16198549 BJNY 8735 BCZR OR AULM K12 MG5 ALL NB2+NA1 16198549 BJNY 8735 BCZR OR AZUT

S/T MD8 ALL NA5/NA6 16198467 BJMT 8495 BARL OR AWHH S/T MD8 ALL NB2 16198473 BJMW 8515 BARM OR AWHF S/T MY2 GU2 NA5/NA6/NB2 16198507 BJNJ 8615 BHSF OR AULR S/T MY2 GU4 NA5/NA6/NB2 16198513 BJNL 8635 BHSH OR AULS S/T MY2 GU6 NA5/NA6/NB2 16198522 BJNN 8655 BHSJ OR AULT

G123/M1 MD8 ALL NA5/NA6 16198480 BJMY 8535 AULN G123/M1 MD8 ALL NB2 16198493 BJNC 8575 AULP L MD8 ALL NA5/NA6 16198487 BJNA 8555 AYAW OR BCNU L MD8 ALL NB2 16198500 BJNF 8595 AYAX OR BCNW

***FOR VEHICLES WITH "COLD KNOCK" HAVING PREVIOUSLY INSTALLED DETONATION FIELD FIX PROM*** - OR - ***FOR VEHICLES WITH "COLD KNOCK" AND DETONATION*** TRANS AXLE EMISSION SERVICE B/C SCAN OLD B/C PLATFORM RPO RPO CLASS PROM KIT CODE I.D. CODE -------- ----- ---- -------- -------- ---- ---- ------- C12/K12 MD8 ALL NA5/NA6 16198457 BJMP 8465 BFNC C12/K12 MD8 ALL NB2 16198463 BJMS 8485 BFND C12 MG5 ALL NA5/NA6 16198532 BJNS 8685 BHSM C12 MG5 ALL NB2 16198546 BJNX 8725 BHUT C12/K12 MT8 ALL NA5/NA6+NA1 16198539 BJNU 8705 BHSN K12 MG5 ALL NA5/NA6+NA1 16198536 BJNU 8705 BHSN C12/K12 MT8 ALL NB2+NA1 16198552 BJNZ 8745 BFND K12 MG5 ALL NB2+NA1 16198552 BJNZ 8745 BFND

S/T MD8 ALL NA5/NA6 16198470 BJMU 8505 BFNF S/T MD8 ALL NB2 16198477 BJMX 8525 BFNH S/T MY2 GU2 NA5/NA6/NB2 16198510 BJNK 8625 BHWN S/T MY2 GU4 NA5/NA6/NB2 16198518 BJNM 8645 BHWP S/T MY2 GU6 NA5/NA6/NB2 16198526 BJNP 8665 BHWR

G123/M1 MD8 ALL NA5/NA6 16198483 BJMZ 8545 BHSA G123/M1 MD8 ALL NB2 16198497 BJND 8585 BHSC L MD8 ALL NA5/NA6 16198490 BJNB 8565 BHSB L MD8 ALL NB2 16198503 BJNH 8605 BHSD

**FOR 1993 LB4 VEHICLES WITH "COLD KNOCK"** ------------------------------------------- S/T M30 ALL NA5/NA6 16211631 BMYC 5245 BCFZ C12/K12 M30 GU4/GU6 NA5/NA6 16205211 BLCU 5225 BBMS C12/K12 M30 GT4/GT5 NA5/NA6 16205214 BLCW 5235 BBMT

1990-95 L05 VIN K

INSTALL THE APPROPRIATE CHECK VALVE OIL FILTER (PF1218 FOR TWO-WHEEL C-SERIES AND FRAM PH3980 FOR FOUR-WHEEL DRIVE K-SERIES). IF THE OIL FILTER DOES NOT CURE THE CONDITION, INSTALL THE APPROPRIATE CALIBRATION FROM THE TABLE BELOW (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 BELOW.

**FOR 1993 L05 VEHICLES WITH "COLD KNOCK" LIGHT DUTY M30 TRANSMISSION* ---------------------------------------------------------------------- SERVICE NEW SCAN OLD APPLICATION AXLE EMISSIONS PART NUMBER B/C CODE I.D. B/C CODE ----------- ---- --------- ----------- -------- ---- -------- C1 PICKUP GU4 NA5/NA6 16205183 BLCL 5155 BJJA C2 PICKUP GU6 NA5/NA6 16205183 BLCL BJJA C1 PICKUP GU6 NA5/NA6 16205191 BLCM 5165 BJJB C2 PICKUP GT4 NA5/NA6 16205191 BLCM BJJB C1 PICKUP GT4 NA5/NA6 16205194 BLCN 5175 BJJC C2 PICKUP GT5 NA5/NA6 16205194 BLCN BJJC K1 ALL GU6 NA5/NA6 16205198 BLCP 5185 BJJD K2 PICKUP GU6 NA5/NA6 16205198 BLCP BJJD K1 ALL GT4 NA5/NA6 16205201 BLCR 5195 BJJF K2 PICKUP GT4 NA5/NA6 16205201 BLCR BJJF C1 SUBURBAN GU6 NA5/NA6 16205201 BLCR BJJF K1 PICKUP GT5 NA5/NA6 16205204 BLCS 5205 BJJH K2 PICKUP GT5 NA5/NA6 16205204 BLCS BJJH C1 SUBURBAN GT4 NA5/NA6 16205204 BLCS BJJH G1/G2 VAN GU6 NA5/NA6 16205208 BLCT 5215 BJJK

**FOR 1994 L05 VEHICLES WITH "COLD KNOCK" LIGHT DUTY M30 TRANSMISSION* ---------------------------------------------------------------------- C10 PU ONLY GU4 NA5/NA6 16209774 BMLD 9725 BJLF C20 ALL GU6 NA5/NA6 16209774 BMLD 9725 BJLF K10 ALL GU6 NA5/NA6 16209774 BMLD 9725 BJLF K20 ALL GU6 NA5/NA6 16209774 BMLD 9725 BJLF C10 ALL GU6 NA5/NA6 16209770 BMLC 9715 BJLH C20 ALL GT4 NA5/NA6 16209770 BMLC 9715 BJLH K10 ALL GT4 NA5/NA6 16209770 BMLC 9715 BJLH K20 ALL GT4 NA5/NA6 16209770 BMLC 9715 BJLH C10 ALL GT4 NA5/NA6 16209782 BMLH 9745 BJLJ C20 ALL GT5 NA5/NA6 16209782 BMLH 9745 BJLJ K10 ALL GT5 NA5/NA6 16209782 BMLH 9745 BJLJ K20 ALL GT5 NA5/NA6 16209782 BMLH 9745 BJLJ G10/G20 ALL NA5/NA6 16209777 BMLF 9735 BJLK

FOR 1995 L05 VEHICLES WITH "SHORT DURATION COLD KNOCK" LIGHT DUTY EMISSIONS 4L60-E TRANSMISSION (M30) ONLY

SERVICE PART NEW B/C OLD B/C APPLICATION AXLE NUMBER CODE SCAN ID CODE

C1 PICKUP GU4 16217748 BPHA 7815 BJYK C2 PICKUP ALL 16217748 BPHA 7815 BJYK K1 SUBURBAN GU6 16217748 BPHA 7815 BJYK C1 UTILITY GU4 16217748 BPHA 7815 BJYK C1 PICKUP, SUBURBAN GU6 16217751 BPHB 7825 BJYL C2 PICKUP GT4 16217751 BPHB 7825 BJYL K1, K2 PICKUP GT4 16217751 BPHB 7825 BJYL C1 UTILITY GU6 16217751 BPHB 7825 BJYL K1 UTILITY GT4 16217751 BPHB 7825 BJYL C1 PICKUP, SUBURBAN GT4 16217753 BPHC 7835 BJYM C2, K2 PICKUP GT5 16217753 BPHC 7835 BJYM G1, G2 VAN GU6 16217757 BPHD 7845 BJYN G1, G2 VAN GT4 16217760 BPHF 7855 BJYP

1990-94 L19 VIN N

INSTALL A CHECK VALVE OIL FILTER; NO OTHER RECOMMENDED ACTIONS AT THIS TIME.

NOTE: THE ABOVE 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.

NOTE: A 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 J8080 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 J8080.

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 FT. LBS.).

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 LBS. FT.) 13. REPEAT FOR EACH MAIN BEARING. 14. REINSTALL OIL PUMP AND SHIELD; TORQUE TO 88 N.M (65 LBS. 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 ----------- ----------- .001" MAIN BEARING KIT, POSITIONS 1-4 ON V8, 1-3 ON V6 10120992 .001" MAIN BEARING KIT, FLANGE #5 ON V8, #4 ON V6 10120994 .002" MAIN BEARING KIT, POSITIONS 1-4 ON V8, 1-3 ON V6 12329758 .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

LABOR OPERATION: J6364 PROM - REPLACE (0.5 HOUR LABOR TIME) J0950 FILTER, OIL - REPLACE J1150 BEARING, CRANKSHAFT MAIN - REPLACE J1880 ENGINE ASSEMBLY - REPLACE (FOR VEHICLES REQUIRING ENGINE REMOVAL TO FIT NEW BEARINGS) T1999 MAIN BEARING CHECK AND REPLACEMENT (WHEN REPLACEMENT IS DONE WITH ENGINE OUT OF THE VEHICLE) (1.7 HRS. LABOR TIME)

USE PUBLISHED LABOR OPERATION TIMES, WHERE APPLICABLE.

FIGURES: 0

GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER." THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION.