Pistons, Rings & Connecting Rods

The pistons are the mechanical components that bear the pressure from combustion that is ultimately turned into vehicle motion. Piston rings form the seal between the pistons and cylinder walls, and the connecting rods connect the pistons to the crankshaft, converting the reciprocating motion of the pistons to the rotating motion of the crankshaft, which turns the gears in the transmission, the axle shafts, and ultimately the wheels. Whether you need to replace any of these parts or want to swap it out for a performance unit, we have your products.

Factory pistons are cast or forged from aluminum alloy. Performance piston material ranges from cast hypereutectic (an alloy with a high silicon content for strength) aluminum that is fine for mildly modified street engines to forged and billet aluminum for high horsepower and racing applications. All pistons are designed and precision machined for superior strength with light weight. Factors that affect piston selection include bore size, compression ratio, and valve clearance. Most pin bores are designed for floating pins retained by clips. Many pistons come with coatings to reduce skirt scuffing, improve surface wear resistance, and reflect heat, which improves durability.

A connecting rod consists of a small end, attached to the piston by a wrist pin, and a big end, which is split so it can be attached to the crankshaft throw, separated by the beam. Factory connecting rods are typically made of cast iron or powdered metal, and aren’t adequate for performance use. Most performance rods are manufactured from forged or billet steel, and there are aluminum rods for drag racing. You’ll find forged rods in I-Beam and H-Beam construction, with the latter generally providing higher strength with less weight. Performance rods are precision made, with uniform center-to-center dimensions, weights, and bore concentricity. They also are commonly bushed for floating pins, have stronger and larger diameter rods bolts, and are available in lengths to suit the desired rod ratio.

The material of stock rings depends on application and the ring’s location on the piston. To handle the heat, top rings are made of ductile iron or steel with a face coating of plasma molybdenum or chromium. Chrome-faced rings are very durable and ideal for engines operated in dusty conditions. Second rings are not exposed to as much heat, and can be made of cast iron. For optimal ring seal, the cylinder wall finish must match the type of ring. Compression rings are split to facilitate installation, leaving a gap when the piston and rings are installed in the cylinder. This gap must be within specs or excessive blow-by can result.

The modern trend in performance piston ring design is for thinner rings, with some of the latest ring packs featuring 1mm top and 2nd rings, and 2mm oil control rings. Thinner rings create less friction while at the same time conforming to the bore better for improved sealing and superior oil control. To ensure durability these rings are made from steel or ductile iron and the compression rings receive a plasma-moly, chrome, or proprietary coating to resist heat and wear. The ring face may also be lapped for faster break-in. Besides less drag and lower weight, thinner rings also allow more options for piston design.