Pontiac Engine >> PISTON SCUFFING AND PIN WEAR ON LIGHT WEIGHT CAST.

Pontiac Engine >> PISTON SCUFFING AND PIN WEAR ON LIGHT WEIGHT CAST.

Piston Scuffing And Pin Wear On
GM 2.5L (151 CID) Engines

Scuffing of piston skirts and excessive piston pin wear are common complaints with General Motors' 2.5L (151 CID) four cylinder engines. Piston pin wear seems to be restricted to OE pistons while the piston scuffing occurred with both OE and aftermarket pistons.

General Motors uses a torque plate during production of these engines and General Motors (Pontiac) engineers recommend using a torque plate to bore and hone these engines. AERA field reports indicate cylinder distortion exceeding .002 when torque plates have been removed from blocks after boring and honing. The two center cylinders are affected the most.

GM has changed the design of this piston a number of times, as well as the type of material used, in efforts to solve a variety of problems. Some aftermarket piston suppliers have followed OE designs while others have not.

Because of the variety of piston designs and differences in materials it becomes extremely important for AERA members to carefully check their piston suppliers's recommendations for fitting these pistons. You must mic the pistons at the point specified by the manufacturer and fit to that manufacturer's
recommended clearances. Using one manufacturer's clearances with
another manufacturer's piston could create problems on this engine.

Piston noise appears to be a bigger complaint than scuffing of piston skirts. This could be due to excessive clearances from not following the piston manufacturer's recommendations. AERA members report decreased customer piston noise complaints when using a torque plate to bore and hone these engines and following the minimum recommended clearances.

Some piston suppliers feel that the pin wear problem is a design problem in how the pin gets its oil supply. Most of the OE pistons oil the pin with oil scrapped from the cylinder walls. If the engine is not properly maintained, contaminants such as carbon deposits and aluminum from top ring poundout can find their way to the pin where they will accelerate wear. Laboratory
analysis has upheld this view in some cases.

The AERA Technical Committee

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