GOOFIT Big Bore Cylinder Rebuild Kit for GY6 50cc 139QMB Racing Scooter Parts 64mm Valve It can be Only Used for GY6 4stroke 49cc 50cc engine upgrade Easy installation with video instruction,you can visit the video on our facebook homepage and Youtube. Best way to get more RPM,maximum upgrade kit for GY6 50cc 139QMB engine and 1P39QMB Engine. Valve Length 64mm ,does not for 69mm one The Belt Cover/CVT Cover Gasket is for a Short Case Version