Oldsmobile Diesel Technical Magazine

5.7L Technical

Piston Differences

There are in fact two different versions of pistons available for the 5.7L Diesel. Which will interchange, but mixing them up is not a good idea. 1978-1981 Engines use pistons that have differnt size intake/exhaust valve reliefs, and must be installed in Left hand and Right hand positions to avoid installing the pistons upside down. In 1982, piston design changed. Valve Reliefs are the same size, eliminating the Left and Right hand versions of the past, and have a notch at the top of the piston near the valve reliefs which must face twards the front of the engine, if it isnt, then the piston would be upside down. These pistons also have a flame slot for better efficiency and reduced emissions. These pistons also have a .045" offset wrist pin which allows smoother, quieter operation. Now this is where it gets important...Installing these pistons upside down, with the valve reliefs at the bottom and the notch facing the rear of the engine, will result in a sort of a rapping noise, which wont go away. The noise may not show up for the first few thousand miles of operation. To avoid this problem when using these pistons, just install them the right way..not upside down.