100cc Big Bore Kit With A9 Cam and Head for Chinese Scooters Mopeds with 50cc, 60cc 4-Stroke GY6 QMB139 engines Head Assembly with 64mm Valves Piston Diameter: 50mm Fits most 4-Stroke GY6/QMB139 engines Some units have a 69mm Valve Head. Please assure you are purchasing the correct one