Choosing the right big bore kit for an M8 107-inch engine can unlock meaningful improvements in displacement and performance. This guide highlights five well-regarded options, including two S&S Cycle kits designed specifically for M8 models and three high-quality alternatives built for GY6-based scooters and ATVs. Whether you seek more torque, higher RPM potential, or a straightforward installation, the selections below cover a range of bore sizes and engineering approaches. Compare compatibility with your M8 model, material quality, and installation considerations to decide which kit best fits your riding goals.
| Product | Brand | Model/Notes | Key Feature |
|---|---|---|---|
| S&S Cycle M8 107 Big Bore Kit | S&S Cycle | 107″/114″ M8 models | Available for both 107″ and 114″ M8 models |
| S&S Cycle M8 114 Big Bore Kit | S&S Cycle | 107″/114″ M8 models | Available for both 107″ and 114″ M8 models |
| Glixal ATMT1-008 47mm Big Bore Kit | Glixal | GY6 80cc 47mm | Inner bore 47mm; piston pin 13mm; durable rings |
| Glixal 52mm Big Bore Cylinder Kit | Glixal | GY6 139QMB 4-Stroke | 52mm bore; 13mm piston pin; for 139QMB 4-stroke |
| GOOFIT 80cc Big Bore Kit | GOOFIT | GY6 80cc 47mm | 47mm bore; 13mm pin; aluminum alloy, wear-resistant |
S&S Cycle M8 107 Big Bore Kit
The S&S Cycle M8 107 Big Bore Kit is designed for M8 engines and is listed as compatible with both 107″ and 114″ M8 models, providing flexibility for upgrading displacement on different M8 platforms. The listing marks the kit as new, reflecting fresh components. From a well-known performance brand, this option is positioned as a reliable upgrade path within the M8 ecosystem.
S&S Cycle M8 114 Big Bore Kit
This kit extends S&S Cycle’s M8 big bore solution to 114″ configurations, while remaining compatible with 107″ M8 models according to the listing. It is described as new and carries the same brand reliability and engineering standards associated with S&S Cycle. The product is positioned for riders seeking a straightforward upgrade path within the M8 family, with a focus on reliable fit and performance.
Glixal ATMT1-008 47mm Big Bore Kit
- Inner Diameter of Cylinder: 47mm
- Outer Diameter of Piston Pin: 13mm
- High Quality Durable Piston Rings
The Glixal ATMT1-008 kit targets GY6 platforms with an 80cc class upgrade and a 47mm bore. It lists 47mm cylinder bore, 13mm piston pin diameter, and durable piston rings as key specifications. While aimed at GY6 engines, this kit provides a sizeable displacement increase option for scooters and light-duty ATVs in need of a big bore upgrade. Users should verify compatibility with their specific M8-adjacent projects before integrating into an M8-based setup.
Glixal 52mm Big Bore Cylinder Kit
- Inner Diameter of Cylinder: 52mm
- Outer Diameter of Piston Pin: 13mm
Glixal’s 52mm big bore kit is designed for the GY6 139QMB 4-stroke engine family. The listing specifies a 52mm cylinder bore and a 13mm piston pin diameter, making it a substantial increase over small-displacement setups. This rebuild kit concept fits scooter and ATV platforms seeking a larger displacement within the GY6 architecture, governed by a 139QMB/139QMA compatibility note in the listing.
GOOFIT 80cc Big Bore Kit
- Inner diameter of cylinder: 47mm
- Outer diameter of piston pin: 13mm
- Replacement for Gy6 49cc, 50cc, 60cc, 80cc engines
GOOFIT’s 80cc big bore kit is designed for the Gy6 family, featuring a 47mm bore and a 13mm piston pin diameter. The listing describes replacement applicability for a range of Gy6 displacements from 49cc up to 80cc, and notes a high-strength aluminum alloy construction with wear-resistant coating. The kit emphasizes a robust structure intended to endure high-load, long-running conditions, potentially lowering long-term maintenance costs for compatible platforms.
Buying Guide
When selecting a big bore kit for an M8 107-inch engine or related platforms, several factors determine the best overall choice. First, confirm model compatibility. The two S&S Cycle options clearly specify M8 compatibility with both 107″ and 114″ configurations, which is crucial for ensuring proper fitment across different M8 builds. For non-M8 options, verify engine family and mounting points to avoid misfits that could compromise performance or reliability.
Bore size is a primary driver of displacement and power potential. The selections in this guide include 47mm and 52mm bores. A larger bore typically increases displacement but may require additional engine work, such as head porting, gaskets, and piston selection. Consider your target performance, intended riding conditions, and the engine’s ability to handle higher pressures without compromising endurance.
Engine design and head configuration matter as well. Some kits, like Glixal 80cc 47mm options, pair a specific cylinder with a non-EGR cylinder head note in the listing, which can affect compatibility with emission controls and exhaust routing on certain builds. Confirm whether your setup uses EGR components and choose accordingly to avoid incompatibilities.
Material quality and component design influence durability and maintenance needs. The Glixal and GOOFIT kits emphasize durable piston rings, aluminum alloy construction, and wear-resistant coatings, all of which contribute to longer service life under high-load operation. For owners prioritizing longevity, these characteristics can be meaningful advantages, especially in daily commuting or extended touring scenarios.
Installation considerations should guide your decision as well. Higher-displacement big bore kits may demand engine reassembly, head work, and precision torquing of fasteners. A well-documented installation guide, compatible gaskets, and proper break-in procedures help preserve engine life after installation. If you are upgrading from a smaller displacement, plan for a professional inspection or at least a thorough DIY teardown and inspection to ensure proper fit and sealing.
Budget and availability play a practical role. Big bore kits vary in price based on bore size, brand, and included components. While S&S Cycle offers the reliability of a branded product within the M8 ecosystem, Glixal and GOOFIT provide cost-conscious alternatives that still emphasize quality materials and robust construction. Check current stock, shipping times, and any required supporting parts to complete the upgrade without delays.
In summary, the best choice depends on your target engine, the exact M8 model you own, and how aggressively you plan to upgrade displacement. For M8 107- or 114-model riders seeking a proven, brand-name option, the S&S Cycle kits remain strong contenders. If you’re exploring non-M8 platforms or broader scooter and ATV applications, the Glixal and GOOFIT options offer credible alternatives with clear bore specifications and compatible accessory notes. Ensure you verify bore size, piston pin diameter, and head compatibility to achieve a reliable, long-lasting upgrade.