In a two‑stroke outboard motor, the pistons fire every revolution, creating high thermal stress. These outboard motor pistons are typically cast from aluminum alloy to save weight. The skirt of an outboard motor piston guides it within the cylinder bore.

Two‑stroke outboard motor pistons include rings that seal compression and control oil. Because the fuel mix lubricates the engine, outboard motor pistons have specially shaped ports. A damaged outboard motor piston can cause scoring on the cylinder wall.

When replacing outboard motor pistons, you must match the oversize to the bore diameter. For small tiller engines, outboard motor pistons are around 2 inches in diameter. The wrist pin connects each outboard motor piston to the connecting rod.

Loose wrist pin retainers can lead to catastrophic failure of the outboard motor piston. After machining, outboard motor pistons are weight‑matched to keep the engine balanced. Many mechanics recommend using genuine outboard motor pistons for proper expansion rates. Regular decarbonizing of outboard motor pistons prevents ring sticking and power loss. For saltwater use, some outboard motor pistons receive a hard anodized coating.