QMB139 50mm Big Bore Cylinder Kit

50mm Big Bore Cylinder Kit for 50cc 4-stroke QMB139 engines. Upgrades to 81.3cc based on a stock stroke of 41.4mm! Includes cylinder, piston, pin, circlips, rings, head gasket and base gasket.

*You may need to modify your engine case to accommodate the larger cylinder.

• Upgrades to 81.3cc!
• Bore: 50mm
• Overall Height: 70mm
• Cylinder Sleeve Outer Diameter: 54.4mm