INCREASED PISTON PIN DIAMETER NEW INFORMATION

VEHICLES AFFECTED: 1990 CHEVROLET LUMINA CARS W/2.5L AND AUTOMATIC TRANSMISSION

In July 1989, 2.5L engines (VIN Code R) used in the 1990 W-cars began to be assembled with increased wall thickness piston pins or "thick wall" pins. Engines built prior to the production breakpoint have "thin wall" pins.

The "thin wall" pins have an I. D. = 15.6 mm to 15.8 mm (0.615 in. to 0.620 in. The "thick wall" pins have an I.D. = 14.4 mm to 14.6 mm (0.567 in. to 0.573 in.

Engines built with the "thick wall" pins may be identified by two methods:

1). ENGINE SERIAL NUMBER: 1990 W-cars with engine numbers greater than 1817906, are equipped with engines having the "thick wall" pins. The engine numbers may be found on a bar-coded label located on the cylinder block near the oil pan rail, see the Illustration. "Thin wall" piston pins were used in engines built prior to the above breakpoint number.

2). ENGINE BROADCAST CODE: The engine broadcast code may be confirmed prior to servicing piston/pin components. Refer to the Illustration for the broadcast code locations.

BROADCAST CODE - BUD: the engine has the "THIN WALL" piston pins.

BROADCAST CODE - BUS: the engine has the "THICK WALL" piston pins.

To determine the proper size of the replacement piston/pin assembly, inspect the top of the piston. The piston will have either the letter "C" or the letters "CC" stamped on the top. To maintain proper engine operation, the replacement pin wall thickness piston lettering must match the old pin wall thickness and piston lettering. Refer to the table below for the respective replacement assembly part numbers:

Tools required for this procedure are Kent-Moore J 24086-88A, piston pin remover and J 24086-107 removal adapter.

PISTON LETTERING PISTON/PIN ASSEMBLY PART NUMBER ---------------- ------------------------------- "Thin Wall" Pin "Thick Wall" Pin --------------- ---------------- C ---------------- 10101711 10112444

CC ---------------- 10101714 10112445

Partial engine assemblies with the thick wall piston pin may be ordered under the following part number:

Broadcast code - BUS P/N 10159541

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.