47mm GY6 50cc (139QMB) Cylinder Kit

47mm Cylinder Kit for 139QMB 50cc Engines

This cylinder kit is built to take a 50cc QMB139 engine up to 72cc. Everything needed for the install is in the box, so it suits anyone wanting a more responsive scooter engine. It is one of the GY6 50cc scooter parts that can noticeably improve acceleration and how the engine responds overall. Note that the engine case may need modifying to make room for the larger cylinder.

What's in the Box

The package includes a cylinder, piston, piston rings, piston pin, circlips, a head gasket and a base gasket. Together these parts are meant to deliver dependable running once fitted. Each piece is sized to sit properly inside the engine, so the upgrade is a fairly direct process for scooter enthusiasts.

Performance and Specifications

The cylinder has a 47mm bore and a sleeve outer diameter of 52.7mm. The wrist pin measures 13mm across, and the overall piston height is 34.4mm. The compression height, measured from the centre of the wrist pin hole to the top edge of the piston, is 17.25mm. These dimensions are what produce the larger displacement and the performance gain.

Specifications

• Cylinder Bore: 47mm
• Wrist Pin Diameter: 13mm
• Total Piston Height: 34.4mm
• Compression Height: 17.25mm
• Included Components: Cylinder, piston, rings, piston pin, circlips, head gasket, base gasket
• Fits: 139QMB-based 50cc engines (GY6-style, 139QMA/QMB family) for 47mm big bore upgrade to 72cc

Fitment

Compatible with:

• 139QMA
• 139QMB
• 1P39QMB
• 1P39QMA-2
• YN139QMB
• JJ1P39QMB
• 139FMA-2
• BD1P39QMB
• BN139QMB
• 147QMD
• Other QMA models
• Other QMB models
• Any engine code containing "QM" or "FM"

How to choose: Check that your engine code appears on the list above. The engine case may need modification to accept the larger 52.7mm sleeve.

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