SINGLE SIZE PISTONS USED IN PRODUCTION

1988 CUTLASS CALAIS WITH 2.5L ENGINE (VIN CODE U)

The following information addresses the recent piston size change made on the 1988 2.5L (VIN Code U) engine.

Improved process control has reduced the piston-to-bore clearance variation on subject engines to the point where pistons of one size can be used. Serviceability has also been improved by reducing the number of service replacement piston sizes.

Beginning with VIN breakpoint JM253906, all 1988 Cutlass Calais models equipped with the 2.5L (VIN Code U) engine are being assembled with "single size" pistons. The single size piston is stamped with the letter "C".

Piston size, cylinder bore diameter, and clearance specifications for the "C" size piston are as follows:

Piston size: 3.9985 + or - .0005 inch (101.5619 + or - .0127 mm).

Bore size: 4.0010 + or - .0005 inch (101.6254 + or - .0127 mm).

Piston to bore clearance: .0015 - .0035 inch (.0381 - .0889 mm).

Service replacement "C" size piston and pin assemblies are available as follows:

Standard: Part Number 10101486

.005 Inch Oversize: Part Number 10101488

Previously, 2.5L (VIN Code U) engines were assembled with a range of six possible different piston sizes stamped with letters "L", "M", "P", "S", "T", or "U". Each piston size was different by .0004 inch (.0010 mm).

The "L" size had the smallest diameter - 3.9982 inch (101.555 mm).

The "U" size had the largest diameter - 4.0006 inch (101.615 mm).

Prior to the piston size change, the piston-to-bore clearance specifications was .0014 - .0022 inch (.0355 - .0558 mm).

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.