Parts - Revised Cylinder Heads
90chevy19Number: 90-246-6A
Section: 6A
Date: May 1990 Corp. Bulletin No.: 936124
Subject: INFORMATION ON NEW DESIGN CYLINDER HEADS
Model and Year: 1986-88 B, F, Y CARS WITH 5.7L (VIN CODE 6, 8) AND 5.0L (VIN CODE H, F, G) ENGINES 1989-90 B, F, Y CARS WITH 5.0L (VIN CODE F) AND 5.7L (VIN CODE 8) ENGINES
CYLINDER HEAD PART NUMBERS:
APPLICATION: 1987 to 1990 F-car with 5.0L, LB9 (VIN F) OR 5.7L L98 (VIN 8) engine
1987 F-car with 5.0L, LG4 (VIN H) engine
1986 to 1990 Y-cars with 5.7L, L98 (VIN 8) engine
1987 to 1988 B-cars with 5.01, LG4 (VIN H) engine
1987 to 1988 B-car with 5.7L, LM1 (VIN 6) engine
This bulletin is being issued to inform dealers of a production change that has been made to the cylinder heads and inlet manifold mounting surface for 1990 5.0L and 5.7L PFI engines. This change will also affect service parts for the past model applications shown above. The change includes a counterbore that has been machined into the two end holes of each cylinder head inlet manifold mounting surface. These counterbores will eventually accept two retainers that will be incorporated into the inlet manifold side gaskets. The intent of these retainers is to hold the inlet manifold gaskets in place during the process of installing the inlet manifold, preventing them from slipping down onto the bolts. This new design head requires the use of four longer bolts than the ones previously used in the location for befter thread clamping load. The current gasket without the retainers is still useable with the counterbore heads and should be used for service until the gaskets with retainers are available.
These counterbored heads are interchangeable with non-counterbored heads, as are the different gaskets that were used on previously built cars.
Parts are currently available from GMSPO.