The best 50cc big bore kit depends on your engine code, bore size, valve setup, and wrist-pin measurement. These five options cover 47mm and 50mm GY6 cylinder kits, complete rebuild sets, and a kit with larger valves. The Glixal 50mm cylinder kit is a focused choice for specified 139QMB/139QMA engines, while the Glixal 100cc complete kit suits buyers seeking a larger-valve assembly. Confirm your engine and existing parts before ordering; “50cc” in a search does not guarantee that every kit fits every 50cc engine.
| Product | Listed configuration | Best suited for |
|---|---|---|
| Glixal Complete 50mm Kit | 100cc; large-valve head | Buyers needing a rebuild kit with a head assembly |
| Glixal 47mm Kit | 80cc; 13mm pin | Buyers comparing a smaller-bore GY6 option |
| Glixal 50mm Cylinder Kit | 100cc; 13mm pin | Specified 139QMB 4-stroke engines |
| Kymlaa 50mm Kit | 100cc; 69mm valve length | Buyers seeking a kit with ignition-related parts |
| HANQIMOTO 50mm Head Kit | 50cc–100cc GY6; 69mm valves | Buyers checking listed valve and pin dimensions |
Glixal Complete 50mm Big Bore Kit
This complete rebuild kit is listed for GY6 139QMB, 139QMA, and 147QMD engines and includes a cylinder head assembly with 18.5/20.5mm valves. The listing contrasts those valves with a stated stock size of 16/18.5mm and identifies the head as a 69mm long-valve style.
Best for: Buyers who want a 50mm, 100cc-oriented kit that includes a larger-valve head assembly. It stands out among these options because the listing describes the head and valve dimensions, not just the cylinder bore.
Check before buying: If the original head has 64mm valves, the listing says rocker arms must be changed to the ones in the kit. Confirm the original head dimensions and engine code first.
Glixal 47mm GY6 Big Bore Kit
This Glixal kit is listed as an 80cc, 47mm cylinder option. Its stated specifications include a 13mm outer-diameter piston pin and durable piston rings.
Best for: Buyers looking for a 47mm kit rather than the 50mm options in this list. The specified bore and pin measurements make it easier to compare against an existing cylinder and piston setup.
Check before buying: The provided product details do not list engine codes or include a cylinder-head assembly. Verify fitment with your engine and determine whether you need additional parts for your repair.
Glixal 50mm GY6 Cylinder Kit
This 50mm Glixal cylinder kit is listed for GY6 139QMB 4-stroke engines and described as a 100cc kit. The stated piston-pin outer diameter is 13mm.
Best for: Owners of the specifically listed 139QMB 4-stroke engine who need a 50mm cylinder kit and have confirmed a 13mm pin measurement. It is a more focused alternative to kits with broader or less specific fitment descriptions.
Check before buying: The listing specifically limits this kit to the 139QMB 4-stroke engine. Do not assume it fits a different engine code, and check whether the kit includes all the parts your rebuild requires.
Kymlaa 50mm Kit With Added Components
The listing describes this as a 100cc big bore kit intended to upgrade certain GY6 50cc, 60cc, and 80cc engines. It specifies a 69mm valve-length version and says the set includes a 6-pin racing CDI, ignition coil, performance spark plug, and clutch spring.
Best for: Buyers who want a 50mm-style upgrade package with the listed ignition and clutch-related components. The extra parts distinguish it from the cylinder-only listings.
Check before buying: The product description says “without EGR,” so it may not suit a setup that requires EGR-related components. Confirm engine configuration and valve length; the listing does not provide a wrist-pin measurement in the supplied details.
HANQIMOTO 50mm Cylinder Head Kit
HANQIMOTO lists this assembly for GY6 50cc–100cc, 4-stroke 139QMB or 139QMI engines. Its specifications include a 50mm cylinder diameter, 69mm valve length, 18mm intake-valve outside diameter, 16mm exhaust-valve outside diameter, and 12.77mm wrist-pin outside diameter. The listing also describes heat dissipation and durability as product features.
Best for: Buyers comparing exact valve and pin dimensions, particularly those checking a 139QMB or 139QMI configuration. It provides more measurements than the supplied details for several other choices.
Check before buying: Confirm all listed dimensions against your engine components. The supplied product information does not clarify every included part, so check the package contents if you need a complete rebuild set.
Buying Guide: How To Choose A 50cc Big Bore Kit
Does the engine code match?
Start with the engine code stamped on or documented for your engine. “GY6” and “50cc” alone are not enough to establish fitment. The Glixal 50mm cylinder kit specifically lists 139QMB 4-stroke engines; the complete Glixal kit also names 139QMA and 147QMD. HANQIMOTO lists 139QMB and 139QMI. Treat these as distinct fitment claims, not interchangeable codes.
Which bore and pin measurements should you check?
Compare the kit’s bore with your intended configuration and check the piston-pin diameter before ordering. The Glixal 47mm kit lists a 13mm pin, while its 50mm cylinder kit also lists 13mm. HANQIMOTO specifies 12.77mm. Do not assume these measurements are interchangeable; verify against the engine’s parts or a qualified mechanic’s guidance.
Do you need a head or a cylinder-only kit?
Choose a kit based on the parts you actually need. The complete Glixal option explicitly includes a cylinder head assembly and larger valves. The Glixal 50mm cylinder listing provides bore and pin details but does not describe a head in the supplied features. Check package contents before purchasing if you are rebuilding more than the cylinder assembly.
Should you choose larger valves or extra components?
Valve length and size matter when matching a head to the engine. The Glixal complete kit calls for a 69mm long-valve style and notes a rocker-arm change in a specified situation. The Kymlaa listing includes ignition and clutch-related parts, while HANQIMOTO provides valve dimensions. Compare those details with your existing setup rather than choosing by the “big bore” label alone.
Frequently Asked Questions
Does every 50cc big bore kit fit a GY6 engine?
No. Fitment depends on the engine code, bore, pin size, valve arrangement, and other configuration details. Use the product’s listed compatibility and measurements to confirm a match.
What does a 50mm bore mean in these listings?
It identifies the listed cylinder’s inner diameter. Some products describe a 50mm kit as a 100cc upgrade, but the exact displacement and fitment claim should be checked for the specific product and engine.
Is a 47mm kit the same as a 50mm kit?
No. The listed cylinder diameters differ. The Glixal 47mm product is described as an 80cc kit, while several 50mm products are described as 100cc kits.
What should I verify before ordering?
Check the engine code, cylinder bore, wrist-pin diameter, valve length and size, EGR configuration if relevant, and included parts. Compare these details with the parts currently installed on your engine.