For riders seeking more power from small-displacement Gy6 engines, a 50cc big bore kit is a common upgrade path. This article highlights five popular options, detailing what each kit changes, its valve geometry, and compatibility notes. Learn how each kit can affect RPM, throttle response, and overall reliability, helping you decide which upgrade best fits your scooter, ATV, or go-kart build.
Summary table of chosen products
| Product | Brand | Core Benefit | Valve Notes |
|---|---|---|---|
| Glixal GY6 100cc 50mm Complete Big Bore Cylinder Rebuild Kit | Glixal | 18.5/20.5mm large valve head increases flow | 69mm valves, may require rocker arm swap |
| Glixal ATMT1-008 80cc 47mm Kit | Glixal | Smaller bore option for reliability | 47mm cylinder, 13mm pin |
| KYMLAA 100cc Big Bore Kit | KYMLAA | Upgrades to 100cc with 69mm valve length version | Simple installation |
| HANQIMOTO Cylinder Head Kit Assy 50mm Big Bore | HANQIMOTO | 69mm valves, robust head assembly | 50mm bore, 18/16mm valve sizes |
| Maoyubelt 47mm Big Bore Kit | Maoyubelt | 47mm bore to 53.2mm potential options | Complete kit with rings and gaskets |
Glixal GY6 100cc Large Valve Big Bore Kit
The Glixal GY6 100cc big bore rebuild kit is designed for 139QMB/139QMA/147QMD engines. It features an 18.5/20.5mm large valve cylinder head assembly, aimed at boosting intake and exhaust flow for more power. The kit is compatible with 69mm long valve style heads. If your original head uses 64mm valves, rocker arms may need upgrading with the kit’s included guidance. This option emphasizes a significant valve-size upgrade to improve higher RPM operation.
Glixal ATMT1-008 80cc Big Bore Kit
The Glixal ATMT1-008 kit expands displacement to 80cc with a 47mm bore. It features a 13mm piston pin diameter and high-quality piston rings to ensure reliable sealing and durability under increased RPM. This option provides a balance between power gain and install ease, making it a popular mid-range upgrade for Gy6-powered machines seeking quicker acceleration without stepping up to a full 100cc kit.
KYMLAA 100cc Big Bore Kit
This KYMLAA 100cc big bore kit is designed to upgrade Gy6 engines from 50cc and above to 100cc. The 69mm valve-length version supports increased flow and improved combustion efficiency. The kit emphasizes a straightforward installation path and aims to deliver higher RPM and more available power without complex modifications. It’s a strong option for riders prioritizing performance improvements with moderate labor.
HANQIMOTO 50mm Big Bore Cylinder Head Kit
The HANQIMOTO head kit targets 139QMA/139QMB engines with a 50mm bore and 69mm valves. The assembly features an intake valve around 18mm and an exhaust valve around 16mm, with 69mm head compatibility. The kit promises improved power, heat dissipation, durability, and stable performance, making it a solid choice for riders focused on head-side enhancements and reliable power delivery at higher speeds.
Maoyubelt 47mm Big Bore Kit
The Maoyubelt 47mm big bore kit is designed for 50cc Gy6 engines, enabling expansion to 47mm bore with a 53.2mm dimension variant. The kit includes essential components: cylinder block, piston, complete ring set, circlips, piston pin, head gasket set, and valve oil seal. It positions itself as a practical upgrade for riders seeking noticeable power gains while maintaining straightforward installation and compatibility with 50cc platforms.
Buying Guide: Key Considerations For Big Bore Kits
When choosing a big bore kit for a Gy6-based machine, consider the following factors to balance performance with reliability:
- Displacement target: Decide whether you want 80cc, 100cc, or a different intermediate upgrade, based on your local legal limits, fuel economy goals, and riding style.
- Valve geometry: Larger intake/exhaust valves can improve high-RPM flow, but may require rocker arm or head modifications. Confirm compatibility with your engine model (139QMB/139QMA/147QMD).
- Head-to-block compatibility: Some sets require 69mm valve-length heads or other head assemblies. Verify your current head’s valve sizes and the need for additional components.
- Installation complexity: Consider whether your kit includes all necessary hardware (gaskets, piston rings, circlips) and whether you need CDI/ignition or clutch changes for safe operation.
- Durability and heat management: Upgrades increase heat and stress on components. Look for kits with reliable piston rings, good cooling compatibility, and robust cylinder walls.
- Installation environment: Ensure you have the tools for precise boring, honing, sealing, and proper torque specs. A professional install is recommended for high-displacement upgrades.
- Maintaining fuel and injector compatibility: High-performance kits may require richer air-fuel mixtures and appropriate carb or EFI adjustments to avoid detonation.
- Legal and warranty considerations: Check local regulations and the manufacturer’s warranty terms for engine modifications beyond stock specs.
In summary, the right big bore kit depends on your machine, performance goals, and willingness to potentially upgrade surrounding components. By weighing valve options, bore size, and installation requirements, you can select a kit that delivers meaningful power gains while preserving reliability for daily use or sport riding.