Naraku 72cc Big Bore Cylinder Kit 42mm - QMB139 / 139QMB

Give your 50cc four-stroke scooter a significant boost of power with the Naraku 47mm 72cc Big Bore Cylinder Kit for compatible QMB139 / 139QMB 49cc and 50cc engines. The larger bore increases displacement to approximately 72cc with the stock 41.4mm stroke, giving you a solid starting point for a more powerful engine setup. The cylinder, piston hardware, and replacement gaskets come together in one kit, so you can spend less time gathering parts and more time on the build.

Key Features

• 72cc Upgrade: 47mm bore produces approximately 72cc when paired with the stock 41.4mm stroke.
• Drop-In Cylinder Design: No crankcase modifications required on compatible engines.
• Matched Piston Components: Includes piston, rings, wrist pin and circlips.
• Gaskets Included: Head, base, exhaust and cam-chain tensioner gaskets support cylinder installation.

Technical Specifications

• Brand: Naraku
• Part number: 137-13
• Manufacturer reference: NK100.47
• Cylinder bore: 47mm
• Displacement: Approximately 72cc with a 41.4mm stroke
• Cylinder sleeve outer diameter: 53.1mm
• Wrist pin diameter: 13mm
• Total piston height: 34.1mm
• Engine type: QMB139 / 139QMB 49cc–50cc four-stroke

What's Included

• Cylinder
• Piston and rings
• Piston wrist pin and circlips
• Head gasket
• Base gasket
• Exhaust gasket
• Cam-chain tensioner gasket

Compatibility

For compatible Chinese-market QMB139 / 139QMB 49cc and 50cc four-stroke scooter engines, including various unlisted makes and models. Compare the original cylinder mounting layout, 53.1mm sleeve clearance, 13mm wrist pin, and piston dimensions before installation. Engine code alone does not guarantee every engine variant matches.

Check cylinder-head compatibility, piston-to-valve clearance, and fueling setup as part of the build; additional tuning or components may be needed for your configuration. 

This product is intended for off-road use only. This product is not intended for use on public roads or land.

• 47mm bore upgrades compatible stock-stroke engines to approximately 72cc
• No crankcase modifications required on compatible engines
• Includes piston, rings, wrist pin and circlips
• Includes head, base, exhaust and cam-chain tensioner gaskets
• Finned air-cooled cylinder

Brand: Naraku; Part number: 137-13; Manufacturer reference: NK100.47; Bore: 47mm; Displacement: approximately 72cc at 41.4mm stroke; Sleeve OD: 53.1mm; Wrist pin diameter: 13mm; Total piston height: 34.1mm; Engine: QMB139/139QMB 49cc–50cc four-stroke; Use: off-road only

Compatible QMB139 / 139QMB 49cc and 50cc four-stroke Chinese scooter engines; various unlisted makes/models. Match mounting layout, 53.1mm sleeve clearance, 13mm wrist pin and piston dimensions. Approximately 72cc with stock 41.4mm stroke. Not for two-stroke engines; off-road use only.