GOOFIT
Big Bore Cylinder Rebuild Kit with 64mm Valves for 4-Stroke GY6 49cc 50cc 139QMB Racing Scooter (80cc/100cc Upgrade)
Big Bore Cylinder Rebuild Kit with 64mm Valves for 4-Stroke GY6 49cc 50cc 139QMB Racing Scooter (80cc/100cc Upgrade)
4.77 / 5.0
(77) 77 total reviews
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Product Overview
Unleash the hidden power of your 50cc scooter with the GOOFIT Ultimate Big Bore Kit. This "Racing Series" package is the maximum performance upgrade for GY6 50cc 139QMB engines, designed to significantly increase RPM and torque. Featuring a precision-machined cylinder and a 64mm valve head, this kit optimizes fuel combustion and enhances engine response, transforming your mild-mannered moped into a high-performance racing machine.
Product Compatibility
This kit is exclusively for the 4-stroke GY6 50cc platform. Please verify your valve length before ordering.
| Category | Compatibility Details |
| Compatible Engines | GY6 49cc / 50cc: 139QMB, 1P39QMB |
| Valve Specification | 64mm Valve Length Only (Does NOT fit 69mm versions) |
| Upgrade Purpose | Maximum RPM & Displacement Boost (80cc/100cc Class) |
| Vehicle Types | Racing Scooters, Mopeds, Mini Quads, Karts |
| Supported Brands | TaoTao, Peace Sports, Wolf, Ice Bear, Bacci, and other GY6 50cc clones |
Specifications
| Attribute | Technical Details & Measurements |
| Engine Type | 4-Stroke Air-Cooled Horizontal |
| Valve Length | 64mm (Short Valve Version) |
| Cylinder Type | High-Performance Big Bore |
| Material | Premium Alloy & High-Temp Resistant Steel |
| Performance Gain | Increased Top Speed & Acceleration |
| Kit Components | Cylinder, Head (with 64mm Valves), Piston Set, Gaskets |
Key Features
- Maximum Racing Upgrade: Specifically engineered to provide the highest displacement boost possible for the 139QMB platform, ensuring more power for uphill climbs and higher top speeds.
- Optimized 64mm Valve Head: The precision-tuned cylinder head features 64mm valves that improve gas flow and prevent overheating during high-speed, high-pressure operation.
- Premium Wear Resistance: All metal components are crafted from high-grade materials, offering exceptional tolerance to heat and friction for a significantly longer engine life.
- Swifter Throttle Response: By optimizing fuel combustion efficiency, this kit delivers smoother engine operation and reduces "lag" during acceleration.
- Comprehensive Reliability: Precision machining of every core component ensures stable performance under demanding racing conditions while reducing the risk of engine failure.
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Fitment FAQ
Will this part fit my specific model and year?
This cylinder piston kit is intended for This kit is exclusively for the 4-stroke GY6 50cc platform. Please verify your valve length before ordering.; Category. Key physical/spec details from the product data include This kit is exclusively for the 4-stroke GY6 50cc platform. Please verify your valve length before ordering., 64mm Valve Length Only (Does NOT fit 69mm versions), Valve Length: 64mm (Short Valve Version). Use the compatibility table and product photos together before ordering.
Do I need to match the OEM part number?
Yes. If your original part has a stamped OEM or manufacturer number, match that number first before ordering. For this cylinder piston kit, also compare the bore diameter, piston-pin size, gasket pattern, stud spacing, engine code, stroke type, and cylinder height. This is especially important for GY6 GY6 models because similar model names can use different parts by year or trim.
What models or situations does this part not fit?
Do not order this cylinder piston kit for machines outside the listed compatibility, or for units with different bore sizes, piston-pin diameters, stroke lengths, stud spacing, or gasket patterns. Do not rely only on the model name or engine size.
What should I check before ordering?
Before ordering, compare your original part with the photos and check the bore diameter, piston-pin size, gasket pattern, stud spacing, engine code, stroke type, and cylinder height. Recheck listed specs such as This kit is exclusively for the 4-stroke GY6 50cc platform. Please verify your valve length before ordering., 64mm Valve Length Only (Does NOT fit 69mm versions), Valve Length: 64mm (Short Valve Version). If any connector, mounting point, size, or year detail is different, confirm fitment before installation.
Only put a few miles as of writing this, however the engine has super high compression and lots of torque compared to my original 50cc on my tao tao 50. I mean seriously, this thing has so much compression I can't even kick over the scooter with all my weight! Hope it breaks in a bit so I can in the future, which I'm sure it will. Everything fit very well. 4 stars as the exhaust stud snapped off when re-attaching my exhaust to the bottom of the engine giving me an exhaust leak. Perhaps just a faulty stud.Came with all the necessary gaskets, and extra gaskets for other parts not involving the engine which is very nice since you may need them at some point upgrading other stuff. Didn't try the weights at all.Make sure to torque everything correctly, and to gap your valves right!
Boost my scooter over stock one,the gaskets are high quality, as is the quality of machining and the surface finish of the piston and cylinder. The included valve seals were an unexpected bonus.
Installed on Jonway Solana 49cc moped. I've only rode it for a few days now but everything installed great, and rocker arm replacements for 69mm valve were included, and installed fine as well. Provides a big power boost alone, even with every other part being stock. I intend to upgrade my carb and exhaust along with it, but It's already running like a beast (40+ at half throttle, Im sure I'll hit 50-60 full throttle after engine break in.). I'm not sure why the product comes with a spare oil pump gear, but Its nice to have anyway. I set both valve lashes to .004mm, It runs fine like that with mild clicking, so your moped, and mine, may need custom adjustment.
The kit fit great, scoot is running real good. Thanks GOOFIT
Should mention all the rest of the products definitely recommended the gy6 owner also upgrade so not causr damage trying to support bigger bore