Description Our 72cc scooter big bore cylinder kit is great for increasing overall performance on small under-powered 50cc QMB139 scooter engines. Engine kit increases engine bore size from 50cc to 72cc and includes everything shown in the image; cylinder, rings, and gaskets. This 72cc scooter engine kit increases low end acceleration as well as top speed. This high performance scooter big bore engine kit is easy to install. Combine with a high performance carburetor and high performance exhaust and get peak performance from your 50cc gas scooter. Note: This high performance cylinder kit is only compatible with 4-stroke 50cc QMB139 engines. Specifications Bore: 47 mm Piston Height: 33 mm Cylinder/Cylinder Head hole spacing: 50 mm x 50 mm Piston Wrist Pin Diameter : 12 mm Piston Wrist Pin Length: 37 mm Compression height : 17 mm Ring Diameter: 47 mm Compatibility Tank Urban 50