Chrysler V-6 reciprocating assemblies

Chrysler’s 2.7/3.2/3.5L V-6 engine is a robust unit that’s seen service in everything from pedestrian Dodge minivans to the Plymouth Prowler exotic. Unlike many mass- market engines, the 2.7/3.2/3.5 family uses some sophisticated technologies in their reciprocating assemblies (pistons and connecting rods) of which techs diving into these blocks need to be aware. Connecting rods are made from powdered metal, which is weighed and poured into an oversize preform mold. The mold is fired in a controlled atmosphere furnace to sinter and fuse the power into solid metal. The now-solid oversize preform is then moved to a forging die, where the part is forged to the final shape. This process is done while the part is still warm. After forging, the rod is shot-peened to remove surface flash and to increase surface hardness. Then the rod’s ends are machined, and the rod bolt holes are drilled and tapped. Rod bolts are installed loosely, and the caps formed by fracturing.

Pistons are cast and machined to a single size and weight for engine balance, and Chrysler sells pistons and rods as a service assembly. Pistons domes have no valve relief’s, which allows Chrysler to move the top ring upward, leaving very little dead space between piston and cylinder wall where unburned hydrocarbons can hide.

What does all this mean to you? On connecting rod service, it’s important to not damage the shot-peened surface by stamping cylinder numbers into the metal. A permanent felt-tip marker is best. Since the piston/rod assemblies are well balanced from the factory, it may seem O.K. to swap them in their bores during reassembly. That’s not only a bad practice from a clearance standpoint, but the use of offset piston pins and oil squirt holes aimed at the major thrust side of the block mean that orientation of the assemblies is extra important during reassembly. Pistons are marked with an arrow, and the pin boss area has a corresponding “F” mark. Both must point toward the front of the engine with the oil squirt hole aimed at the cylinder thrust face. These engines rotate clockwise, so the left bank thrusts to the center of the engine, while the right thrusts to the outside of the block. And those non-existent valve relief’s? This means that the engine isn’t freewheeling, so rotate the engine first by hand if your service can alter valve timing in any way.