GY6 50cc (139QMB) Cylinder & Head Kit for 39/47/50mm

GY6 50cc Cylinder and Head Kit for QMB139 Engines

This full cylinder and head set suits QMB139 4-stroke 50cc engines and covers everything needed for a complete top-end rebuild. It comes in three bore options: 39mm (stock), 47mm (72cc upgrade), and 50mm (81.3cc upgrade). Whether you are doing routine service or looking for more power, it is one of the GY6 50cc scooter parts that can make a noticeable difference when fitted correctly.

What's in the Box

Each kit includes a cylinder head, cylinder, piston, piston rings, piston pin, retaining clips, head gasket, and base gasket. All parts are made to fit the QMB139 engine platform. If you choose a larger bore, you may need to modify the engine case to make room for the new cylinder dimensions.

Fitting Advice

Swapping the cylinder and head is a job many scooter owners tackle at home, provided they have the right tools. Follow proper fitting steps closely to avoid engine problems. This kit suits anyone wanting more performance or looking to replace worn components.

Specifications

• Cylinder Bore: 39mm (stock), 47mm (72cc upgrade), 50mm (81.3cc upgrade)
• Cylinder Sleeve OD: 45mm (39mm), 52.8mm (47mm), 53.95mm (50mm)
• Wrist Pin Diameter: 13mm
• Total Piston Height: 34.4mm
• Compression Height: 17.25mm
• Intake and Exhaust Valve Length: 64mm
• Head Type: Non-emissions
• Fits: QMB139 (139QMB) 49cc/50cc 4-stroke engines, 39mm stock or 47mm/50mm bore upgrade

Compatibility

Fits:

• Buddy 50
• RoughHouse 50
• Rattler 50
• Other QMB139-powered scooters (39mm stock bore; 47mm and 50mm may need engine case modification)

Choosing a bore: Pick the bore that fits your build: 39mm for stock, 47mm for the 72cc upgrade, or 50mm for the 81.3cc upgrade. Larger bores may require case modification.

Browse related parts: GY6 50cc Scooter Parts (139QMB) · GY6 Scooter Parts · Scooter Parts