Product Description
80cc (47mm) BIG BORE CYLINDER KIT – STYLE #2
FOR QMB139 / 139QMB 50cc 4-STROKE SCOOTER ENGINES
COMPLETE TOP END REBUILD KIT – INCLUDES 69mm VALVE CYLINDER HEAD
Upgrade your stock 50cc QMB139 engine to a larger 47mm big bore setup for increased power, improved acceleration, and better hill-climbing performance. This complete top-end kit includes a pre-assembled non-EGR cylinder head with large 69mm valves, making it an excellent replacement or performance upgrade for worn or damaged engines.
⭐ FEATURES
- Complete 47mm Big Bore Upgrade Kit
- Converts most stock 50cc QMB139 engines to approximately 72cc (commonly marketed as 80cc)
- Brand new components
- Non-EGR performance cylinder head
- Large 69mm valve head installed and assembled
- Direct replacement for most QMB139 engines
- Great for engine rebuilds or restoring lost compression
- Increased torque and throttle response
- Improved acceleration over stock displacement
- Excellent replacement for damaged or worn cylinders
- Precision-machined aluminum cylinder
- Cast iron cylinder sleeve for long service life
- Lightweight aluminum piston
- Ready for installation with included gaskets
KIT INCLUDES
- 47mm Cylinder
- Non-EGR Cylinder Head
- 69mm Valves (Installed)
- Valve Springs Installed
- Valve Seals Installed
- Piston
- Complete Piston Ring Set
- Wrist Pin
- (2) Wrist Pin Circlips
- Cylinder Base Gasket
- Cylinder Head Gasket
SPECIFICATIONS
Engine Type
- QMB139 / 139QMB
- Air-Cooled
- Single Cylinder
- 4-Stroke
Cylinder Bore
- 47mm
Approximate Displacement
- 72cc (commonly referred to as 80cc)
Cylinder Material
- Aluminum with Cast Iron Sleeve
Cylinder Head
- Aluminum
Head Style
- Non-EGR
Valve Length
- 69mm
Cooling
- Air Cooled
PERFORMANCE BENEFITS
✔ More low-end torque
✔ Better acceleration
✔ Improved hill-climbing ability
✔ Better carrying power with heavier riders
✔ Restores engine compression
✔ Excellent replacement after engine damage
✔ Works with factory CVT transmission
✔ Great foundation for additional performance upgrades
RECOMMENDED UPGRADES
(Not Included)
- Performance CDI
- Performance Ignition Coil
- Larger Main Jet
- Performance Air Filter
- Performance CVT Variator
- Performance Drive Belt
- Lightweight Roller Weights
- Torque Spring
- Performance Clutch
- High Flow Exhaust
FITMENT
Fits many Chinese scooters equipped with the QMB139 / 139QMB 50cc 4-stroke engine, including many models from:
- TaoTao
- Ice Bear
- Wolf Brand Scooters
- Jonway
- Roketa
- Tank
- Peace Sports
- Gator
- JMStar
- SUNL
- BMS
- Dongfang
- NST
- Baja
- Kazuma
- Redcat
- Puma
- Eagle
- Lifan (QMB139 models)
- Znen-built scooters
- Many other Chinese-built scooters using the QMB139 engine
IMPORTANT FITMENT INFORMATION
Please compare your original parts with the photos before purchasing.
Chinese scooters often have production changes, and not every 50cc scooter uses the same cylinder head or engine configuration.
This kit is designed for QMB139 50cc 4-stroke engines only.
Will NOT fit:
- QMJ157 / GY6 125cc
- QMJ157 / GY6 150cc
- Minarelli 2-Stroke Engines
- Genuine Buddy 50 (2-Stroke)
- Yamaha Zuma 2-Stroke
- Honda Ruckus
- Honda Metropolitan
INSTALLATION NOTES
- Professional installation is recommended.
- Check valve lash after installation.
- Always use new engine oil after installation.
- Verify piston ring end gap before assembly.
- Lubricate piston, rings, wrist pin, and cylinder during installation.
- Heat-cycle the engine properly after installation.
- Avoid prolonged full throttle during the break-in period.
BREAK-IN RECOMMENDATIONS
For maximum engine life:
- Vary engine RPM during the first 100 miles.
- Avoid sustained wide-open throttle.
- Change engine oil after the first 100–150 miles.
- Recheck valve adjustment after break-in.
WHY UPGRADE TO A 47mm BIG BORE?
A larger bore increases engine displacement, allowing the engine to move more air and fuel with every combustion cycle. The result is:
- Stronger acceleration
- Increased usable torque
- Better climbing performance
- Improved overall rideability
- More responsive throttle
- Excellent value compared to a complete engine replacement
Note: Although these kits are commonly marketed as "80cc," a standard 47mm bore with the stock QMB139 crankshaft produces approximately 72cc of actual engine displacement. Listing it as "80cc" remains common in the scooter industry because it matches the terminology buyers search for on eBay.
