QMB 139 50cc GY6 Big Bore Kit. This kit will change your stock 39mm bore to 44mm bore (60cc). Some people call them 70cc or 80cc kits but they are actually 60cc. 

Included:

• 44mm Cylinder
• 44mm Piston with rings and wrist pin
• Cylinder Head
• Upper Gasket Set
• Free High Performance Cam Shaft Part # 160-001