VALVETRAIN/LIFTER NOISE (ADJ. LASH/INST. ADJUSTABLE LASH). GMC Truck GMC C Pickup

********************************************************************* SUBJECT: VALVETRAIN/LIFTER NOISE (ADJUST LASH/INSTALL ADJUSTABLE LASH)

MODELS: 1992-93 C/K AND S/T TRUCKS; M/L AND G VANS WITH LB4 4.3L V6 TBI (VIN Z) OR L35 4.3L V6 CPI (VIN W) ENG.

********************************************************************* THIS BULLETIN CANCELS AND SUPERSEDES CORPORATE BULLETIN 376107. PLEASE DISCARD PREVIOUS DIVISIONAL PUBLICATIONS: CHEVROLET BULLETIN 93-173-6A GMC TRUCK BULLETIN 93-6A-68 CANADA BULLETIN 93-6A-126 *********************************************************************

CONDITION:

SOME OWNERS MAY REPORT A TICK, CLICK, OR CLATTER NOISE OCCURRING ON START UP, WITH THE ENGINE HOT AND/OR COLD. THIS VALVETRAIN/LIFTER NOISE MAY LAST UP TO ONE MINUTE.

CORRECTION:

TO ELIMINATE THE NOISE, USE THE APPROPRIATE PROCEDURE BELOW. IN DETERMINING WHICH PROCEDURE IS APPROPRIATE, INSPECT THE ENGINE IDENTIFICATION NUMBER STAMPED ON THE ENGINE BLOCK. THE ATTACHED DIAGRAMS SHOW THE LOCATION OF THE ENGINE IDENTIFICATION NUMBER ON THE BLOCK. USE PROCEDURE 1 FOR ENGINES WITH A "W" IN THE SOURCE CODE LOCATION (FIRST POSITION). USE PROCEDURE 2 FOR ENGINES WITH A "T" IN THE SOURCE CODE LOCATION.

PROCEDURE 1

FOR LB4 ENGINES WITH A "W" IN THE SOURCE CODE LOCATION. THESE ENGINES HAVE PRESSED-IN STUDS AND AN ADJUSTABLE LASH VALVETRAIN.

UNLASH ALL INTAKE AND EXHAUST VALVES. USING THE VALVE LASH PROCEDURE OUTLINED IN THE SERVICE MANUAL, LASH THE VALVES IN 1.75 TURNS DOWN FROM ZERO LASH (NOT 1 TURN).

PROCEDURE 2

FOR L35 ENGINES OR LB4 ENGINES WITH A "T" IN THE SOURCE CODE LOCATION. THESE ENGINES HAVE SCREW-IN STUDS AND A NET LASH VALVETRAIN.

REMOVE OLD ROCKER ARM NUTS, ROCKER ARMS, ROCKER BALLS, AND STUDS FROM THE CYLINDER HEAD AND DISCARD. INSTALL ADJUSTABLE LASH SERVICE STUDS P/N 476530. TORQUE ADJUSTABLE LASH SERVICE STUDS TO 47 N.M (35 LBS. FT.). INSTALL ROCKER ARMS P/N 10066063. INSTALL BALL P/N 14091813 AND NUT P/N 477212. USING THE VALVE LASH PROCEDURE FOR ADJUSTABLE LASH VALVETRAIN (PRESSED-IN ROCKER ARM STUD PROCEDURE) OUTLINED IN THE SERVICE MANUAL, LASH THE VALVES TO 1.75 TURNS DOWN FROM ZERO LASH (NOT 1 TURN).

NOTE: 1991 NET LASH LB4 ENGINES MAY BE CONVERTED TO AN ADJUSTABLE LASH SYSTEM USING THESE SAME PART NUMBERS. HOWEVER, IF THE 1991 LIFTERS ARE RETAINED, THE VALVES SHOULD BE LASHED TO 1 TURN DOWN FROM ZERO LASH.

PARTS INFORMATION:

DESCRIPTION PART NUMBER QUANTITY ----------- ----------- -------- ADJUSTABLE LASH SERVICE ROCKER STUD 476530 12 PIVOT (ROCKER) BALL 14091813 12 ROCKER ARM NUT 477212 12 ROCKER ARM 10066063 12

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

LABOR TIME:

PROCEDURE 1: J0587 USE APPROPRIATE LABOR TIME GUIDE PROCEDURE 2: T7696 - FOR VEHICLES WITH TONAWANDA BUILT ENGINES OR GMSPO GOODWRENCH REPLACEMENT ENGINES. M/L VAN 1.5 HOURS (ADD 1.1 WITH REAR AIR CONDITIONING) S/T TRUCK 1.2 HOURS G VAN 1.5 HOURS C/K TRUCK 1.2 HOURS

FIGURES: 2

Object Number: 83082 Size: FS

Object Number: 95388 Size: SF

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.