Engine - Valvetrain/Lifter Noise
Group Ref.: EngineBulletin No.: 376006
Date: December, 1993
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) ENGINE
THIS BULLETIN CANCELS AND SUPERSEDES CORPORATE BULLETIN 376107. PLEASE DISCARD PREVIOUS DIVISIONAL PUBLICATIONS: (see illustration)
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.
SERVICE PARTS INFORMATION:
Parts are currently available from GMSPO.
WARRANTY INFORMATION:
Note:
Labor operations are coded to base vehicle coverages in the warranty system.