Description Here is a 50cc 139QMB scooter go-kart engine crankcase cover for those popular 4-stroke 139QMB engines that put the power to so many of today’s 49/50cc motor scooters. These are probably the most common scooter and go-kart engines, and many millions have been made over the years. Two styles are available, the long case and the short case versions. Both sport a nice black finish. The short case engine is designed for use with 10″ diameter rear rims. This would correspond to a tire size of 2.75-10 through 3.50-10. A short case engine will not accommodate rear tires that are larger than 3.50-10. The long case engine is designed to allow the use of 12″ rear rims. This would correspond to a tire size of 110/70-12 through 140/70-12. Please use your rear tire size to determine which crankcase cover is right for your go-kart or street-legal motor scooter. Compatibility Coleman Powersports JL50QT-14