S&S 107 Replacement Piston Kit S&S has a long history of developing performance components for Harley engines, and this 107 replacement piston kit continues that tradition. Designed to work with stock 4-3/8 stroke flywheels, it helps take your engine to 107 displacement with quality components from a trusted name. Features: Works with stock 4 3/8 stroke flywheels to increase displacement to 107 Stock cylinders may be bored to accommodate larger pistons, but S&S recommends using their 3.937 bore cylinders, which feature high-strength alloy cast-iron liners 10.4:1 compression using stock heads Pistons are complete with rings, wristpins, and wristpin clips 3.937 standard bore