Bel-Ray Thumper Gear Saver Transmission Oil Bel-Ray Thumper Gear Saver Transmission Oil is a premium 4-stroke transmission oil that has been developed for the unique demands of 4-stroke motorcycles equipped with separate engines and transmissions. Formulated with extra protection for gears and bearings subject to high torque loads of todays powerful 4-stroke Thumper engines. This multi-viscosity formula flows freely for better clutch cooling and provides positive clutch engagement for better starts and longer clutch life while protecting highly-loaded gears from wear, ensuring smooth shifts for more positive action.