Naraku Super Transmission Kit for 50cc QMB139 engines. Kit includes: Variator, Variator Drive Face, Belt, Torque Spring Base, Clutch and Clutch Bell. Choose from either belt length 669mm or 788mm in the drop down menu. The 669mm length belt is for short case engines that use a 10" rear wheel. The 729mm belt is for long case engines with 12" rear wheel. The 788mm length belt is for extra long case engines, like are found on the Maddog 50cc Ruckus clone.