IJS WaveRunner piston kit is a set of components that are used to repair or replace the pistons in the engine of a Yamaha WaveRunner personal watercraft (PWC). A WaveRunner piston kit typically includes new pistons, rings, and wrist pins, as well as any other necessary components such as gaskets or seals. It is designed to fit specific models of Yamaha WaveRunner engines and is intended to be used as a complete set to rebuild or refresh the engine's pistons.

The pistons in a WaveRunner engine are a key component of the reciprocating (up and down) motion system. They are located in the cylinder of the engine and are connected to the crankshaft via a connecting rod. As the crankshaft rotates, the pistons move up and down in the cylinder, compressing and expanding the fuel-air mixture and producing power.

WaveRunner piston kits are an important part of personal watercraft engine maintenance and repair, as they allow for the replacement of worn or damaged pistons. They are typically made from high-strength materials such as aluminum or forged steel, and are designed to withstand the high temperatures and pressures that are common in marine environments.