Big Bore Cylinder upgrade kit from 50cc to 80cc for GY6 139QMB 50cc
This is a kit for upgrading your 50cc scooters to 80cc offering better and stronger power.
This kit is for most of Chinese 139QMB Scooters. Kit includes
- Cylinder Head
- Cylinder
- Piston
- Piston Ring
- Piston Pin
- Clips
- Gasket
- Base Gasket
Please note that Jet Size of Carburetor need to be changed as well.
- Upgrades to 80cc
- Cylinder Bore: 50mm
- Wrist Pin Diameter: 13mm
- Total Piston Height: 34.8mm
- Compression Height (from center of wrist pin hole to top edge of piston): 18.3mm
- Please see below for measurements
Size Measurement
This Big Bore Kit increase 50cc engine to 80cc. Some of the Chinese Factories or Distributors will tell you that this kit will upgrade your engine to 97cc or 100cc which is NOT correct information.
Below Table is the technical details of the original engine before install this kit and after.
|
From |
To |
|
| Cylinder (mm) |
39 |
50 |
| Piston displacement (mm) / Stroke (mm) |
41.5 |
41.5 |
| Total Engine Displacement (cc) |
49.6 |
81.5 |
The formula to calculate this is;
(Bore size * Bore size) * Stroke * 0.7857 / 1000 = Total Displacement.