1986 - 1990 Corvette: Service Bulletin: New Design Cylinder Heads Production Change Information

Subject: NEW DESIGN CYLINDER HEADS PRODUCTION CHANGE INFORMATION
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

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 5.0I, LG4 (VIN H) engine
1987 to 1988 B-car with 5.7L, LMI (VIN 6) engine

Source: Chevrolet Service Bulletin
Bulletin Number: 90-246-6A - (04/26/1990)

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.OL 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 better 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.

CYLINDER HEAD PART NUMBERS

YEAR ENGINE VIN CAR PART NUMBER CODE LINE

1986-90 5.7L 8 Y 10125374 Head Asm. - Cylinder (Partial)

1986-90 5.7L 8 Y 10108661 Bolts, 2 required per counter-bored head

1987 5.0L H F 10159553 Cylinder Head and Stud Asm.

1987-90 5.7L 8 F 10159552 Cylinder Head and Stud Asm.

1987-90 5.0L F F 10159553 Cylinder Head and Stud Asm.

1987-88 5.0L H B 10159553 Cylinder Head and Stud Asm.

5.7L 6 B 10159553 Cylinder Head and Stud Asm.

Parts are currently available from GMSPO.

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.