A strong choice for a 50cc scooter is a GY6-compatible kit that matches the engine code, valve length, and desired bore; it suits owners upgrading a 139QMB or 139QMA engine. These options range from 47mm kits described as upgrades to 80cc to 50mm kits described as 100cc upgrades, with some adding a cylinder head, camshaft, oil pump, CDI, and ignition coil. Fit is not universal: several listings distinguish 64mm from 69mm valve-length heads, and one specifies a 12.77mm wrist pin.
Check your existing engine and head before choosing, rather than relying on the scooter’s advertised displacement alone. The ranking favors clear fitment details and useful included components, while noting where a kit’s stated compatibility is narrower.
The KYMLAA 100cc Big Bore Kit leads because its listing identifies a 50mm bore and 69mm valve-length version and includes cylinder and head kits, camshaft, gaskets, oil pump and gear, spring sets, CDI, coil, and spark plug. It is aimed at compatible 139QMB GY6 scooters, not every 50cc scooter. Confirm your engine code and valve length before ordering; its listed fitment examples and no-EGR description should not replace checking the parts on your engine.
Our Top Picks
Best OverallIts 50mm, 69mm-valve version is listed for GY6 upgrades and includes cylinder and head kits, camshaft, oil pump, CDI, coil, and spark plug.
View on Amazon
Most Complete KitThe 50mm upgrade kit lists a 69mm valve version and bundles cylinder and head kits, camshaft, oil pump, CDI, ignition coil, and spark plug.
View on Amazon
Large-Valve HeadThis 50mm kit includes a 69mm-style head with 18.5/20.5mm valves, plus a racing CDI and ignition coil; rocker-arm compatibility needs checking.
View on Amazon- 69mm Head Kit ZTDZZH 69mm Valve Head Kit
- 47mm Bore Option TRKIMAL 80cc Cylinder Kit
Compare these GY6 big bore kit options
| # | Product | Weight | Package Dimensions | Buy |
|---|---|---|---|---|
| 1 | 1. KYMLAA 100cc Big Bore KitBest Overall | 6.6 lb | 10.31 x 7.24 x 6.18 in | View on Amazon |
| 2 | 2. TRKIMAL 100cc Big Bore KitMost Complete Kit | 6.6 lb | 10.28 x 7.24 x 6.18 in | View on Amazon |
| 3 | 3. Glixal 100cc Large-Valve KitLarge-Valve Head | 8.34 lb | 16.5 x 12.05 x 4.09 in | View on Amazon |
| 4 |  4. Glixal 100cc Cylinder KitFocused 50mm cylinder rebuild | 2.18 lb | 5.59 x 5.2 x 4.61 in | View on Amazon |
| 5 |  5. ZTDZZH 69mm Valve Head Kit69mm Head Kit | 4.4 lb | 6.61 x 6.18 x 6.02 in | View on Amazon |
| 6 | 6. ZTDZZH 64mm Valve Head Kit64mm-valve GY6 top end | 4.33 lb | 6.26 x 6.14 x 5.98 in | View on Amazon |
| 7 |  7. GOOFIT 64mm Valve Kit64mm-valve 50cc rebuild | 5.15 lb | 11.02 x 8.31 x 4.06 in | View on Amazon |
| 8 |  8. HANQIMOTO 69mm Head Kit12.77mm-pin 69mm head kit | 4.67 lb | 12.99 x 8.07 x 5.51 in | View on Amazon |
| 9 |  9. TRKIMAL 80cc Cylinder Kit47mm Bore Option | — | — | View on Amazon |
| 10 |  10. Chanoc 80cc Cylinder Kit47mm hill-climb upgrade | 2.15 lb | 5.39 x 4.69 x 3.5 in | View on Amazon |
Detailed Reviews: Best Big Bore Kit For 50Cc Scooter
#1 · Best Overall
1. KYMLAA 100cc Big Bore Kit
- Weight: 6.6 lb
- Package Dimensions: 10.31 x 7.24 x 6.18 in
Best for: Broad 100cc rebuild package.
Why it ranks #1: Its 50mm, 69mm-valve version is listed for GY6 upgrades and includes cylinder and head kits, camshaft, oil pump, CDI, coil, and spark plug.
The KYMLAA kit combines a 50mm 100cc upgrade with a long list of engine and ignition components, including a camshaft, oil pump, and six-pin racing AC CDI. That broad package suits a 69mm-valve-length GY6 rebuild where replacing several systems together is useful.
The kit is specified for 69mm valve length and lists cylinder-body and head kits, camshaft and seat, gaskets, oil pump and gear, springs, and copper rollers. Those components make it a more extensive rebuild package than a cylinder-only set, while the six-pin racing AC CDI, ignition coil, and three-electrode spark plug cover listed ignition items. The seller identifies several 49cc and 50cc four-stroke scooter applications, including Jonway, Agility, People S50, and Baotian models.
- 50mm big-bore kit stated to upgrade 50cc, 60cc, or 80cc GY6 engines to 100cc
- Includes cylinder body and head kits
- Lists camshaft, oil pump and gear, gaskets, springs, and rollers
- Includes six-pin AC CDI, ignition coil, and three-electrode spark plug
- The 69mm valve-length version is not the listed choice for 64mm-valve setups.
Skip it if you need 64mm valves or a smaller cylinder-only parts selection; the listed package is specifically the 69mm-valve version.
This package fits a buyer planning a broader 69mm-valve GY6 rebuild, particularly on the listed four-stroke scooter applications. Its many included components can support coordinated replacement, but valve length and the six-pin CDI specification matter.
Full product details
| Brand | KYMLAA |
|---|---|
| Item Weight | 6.6 pounds |
| Item model number | KYMLAA-00050-1 |
| Manufacturer | KYMLAA |
| Part Number | KYMLAA-00050-1 |
| Package Dimensions | 10.31 x 7.24 x 6.18 inches |
#2 · Most Complete Kit
2. TRKIMAL 100cc Big Bore Kit
- Weight: 6.6 lb
- Package Dimensions: 10.28 x 7.24 x 6.18 in
Best for: 69mm-valve complete upgrade.
Why it ranks #2: The 50mm upgrade kit lists a 69mm valve version and bundles cylinder and head kits, camshaft, oil pump, CDI, ignition coil, and spark plug.
A camshaft, oil pump and gear, and six-pin racing AC CDI join the 50mm cylinder and head components in TRKIMAL’s 100cc upgrade kit. That combination targets a 69mm-valve GY6 rebuild where the buyer wants more than the basic bore parts.
TRKIMAL states that the kit upgrades GY6 50cc, 60cc, or 80cc engines to 100cc without EGR. Its 69mm valve-length specification narrows the fit, while the cylinder-body and head kits, camshaft, camshaft seat, and gaskets cover several core rebuild components. An oil pump and gear, spring sets, and copper roller sets broaden the included engine parts; the six-pin AC CDI, ignition coil, and three-electrode plug add listed ignition pieces.
- 50mm big-bore upgrade stated for 50cc, 60cc, and 80cc GY6 engines
- 69mm valve-length cylinder and head kit
- Includes camshaft, camshaft seat, and gasket kits
- Lists oil-pump parts, springs, copper rollers, CDI, coil, and spark plug
- The specified 69mm valve length does not suit a 64mm-valve setup.
Skip it if you need a 64mm-valve head or are seeking only a basic 47mm 80cc cylinder kit rather than this 50mm 100cc package.
Choose this for a compatible 69mm-valve GY6 rebuild that benefits from bundled camshaft, oil-pump, and ignition parts. The 50mm bore and 100cc upgrade claim are central; the valve-length specification is the key boundary.
Full product details
| Brand | TRKIMAL |
|---|---|
| Item Weight | 6.6 pounds |
| Item model number | TRKIMAL-00192-1 |
| Manufacturer | TRKIMAL |
| Part Number | TRKIMAL-00192-1 |
| Package Dimensions | 10.28 x 7.24 x 6.18 inches |
#3 · Large-Valve Head
3. Glixal 100cc Large-Valve Kit
- Weight: 8.34 lb
- Package Dimensions: 16.5 x 12.05 x 4.09 in
Best for: Large-valve GY6 rebuild.
Why it ranks #3: This 50mm kit includes a 69mm-style head with 18.5/20.5mm valves, plus a racing CDI and ignition coil; rocker-arm compatibility needs checking.
The 18.5/20.5mm large-valve head is the defining feature of Glixal’s 50mm GY6 kit, pairing larger valves with a 100cc upgrade configuration. It suits a 139QMB, 139QMA, or 147QMD rebuild where the head and supporting ignition parts are part of the planned work.
The 50mm cylinder block and piston set provide the core of the stated 100cc rebuild, while the 69mm long-valve-style head sets an important compatibility boundary. Two A7TJC spark plugs, a racing AC-fired CDI with cable pigtail, and a racing ignition coil add ignition components to the package. DLC-coated piston rings are described as wear resistant and friction reducing. Owners whose original head has 64mm valves must change rocker arms using the ones included in the kit.
- 50mm cylinder block and piston set with rings
- 18.5/20.5mm large-valve head assembly
- DLC wear-resistant, friction-reducing piston-ring coating
- Includes CDI, cable pigtail, ignition coil, and two spark plugs
- Original 64mm-valve heads require the included rocker-arm change.
Skip it if you have a 64mm-valve head and do not want to change rocker arms, or need a kit limited to a basic cylinder-and-piston refresh.
Choose this for a compatible GY6 139QMB, 139QMA, or 147QMD project that calls for a 50mm bore and larger-valve head. Its 69mm valve style and rocker-arm requirement for 64mm heads are key fit considerations.
Full product details
| Brand | Glixal |
|---|---|
| Item Weight | 8.34 pounds |
| Item model number | ATMT1-010ML69 |
| Manufacturer | Glixal |
| Part Number | ATMT1-010ML69 |
| Package Dimensions | 16.5 x 12.05 x 4.09 inches |
#4
4. Glixal 100cc Cylinder Kit
- Weight: 2.18 lb
- Package Dimensions: 5.59 x 5.2 x 4.61 in
Best for: Focused 50mm cylinder rebuild.
Why it ranks #4: Its 50mm cylinder kit is explicitly for GY6 139QMB 4-stroke engines and includes the cylinder, piston, rings, pin, seals, and gaskets.
Glixal’s 50mm cylinder kit is specified as a 100cc upgrade for GY6 49cc, 50cc, 60cc, and 80cc engines. Its focused cylinder-and-piston package suits a 139QMB four-stroke rebuild that does not call for a bundled cylinder head or ignition system.
The kit includes a cylinder, piston, rings, pin, and pin clip, providing the central parts for the stated 50mm-bore conversion. Valve oil seal, gaskets, tensioner gasket, exhaust gasket, intake and exhaust studs, and an exhaust nut extend the package to related sealing and mounting hardware. Glixal specifically limits use to the GY6 139QMB four-stroke engine, making engine designation an essential fit boundary rather than a general fit for every GY6 configuration.
- 50mm bore specified for a 100cc upgrade
- Includes cylinder, piston, rings, pin, and clip
- Lists valve oil seal and several gaskets
- Includes intake and exhaust studs and exhaust nut
- The stated application is limited to the GY6 139QMB four-stroke engine.
Skip it if you have a different engine designation or need a head and ignition components included with the cylinder parts.
Choose this for a 139QMB four-stroke project needing a 50mm cylinder rebuild and its listed sealing hardware. It is a focused package, so buyers needing a cylinder head or ignition parts should look elsewhere.
Full product details
| Brand | Glixal |
|---|---|
| Item Weight | 2.18 pounds |
| Item model number | ATMT1-011 |
| Manufacturer | AT MOTOR PARTS |
| Part Number | ATMT1-011 |
| Model | 139QMB |
| Package Dimensions | 5.59 x 5.2 x 4.61 inches |
Listed on Amazon as: GY6 100cc 50mm Big Bore Cylinder Kit for 139QMB 139QMA Engine
View on Amazon#5 · 69mm Head Kit
5. ZTDZZH 69mm Valve Head Kit
- Weight: 4.4 lb
- Package Dimensions: 6.61 x 6.18 x 6.02 in
Best for: 69mm-valve head assembly.
Why it ranks #5: It combines a 50mm cylinder block and head for 139QA/139QMB engines, clearly specifying 69mm valve length rather than 64mm.
The 69mm valve length distinguishes this 50mm-bore ZTDZZH kit from the brand’s 64mm-valve version. It targets a GY6 50cc-to-100cc 139QA or 139QMB rebuild where the head and cylinder block assembly are needed together.
The package lists a cylinder head and cylinder block assembly, bringing the main top-end pieces together for the stated 50mm bore. Its 69mm valve length is explicitly not 64mm, so checking the existing configuration is central to choosing it. Intake-pipe and exhaust-pipe screws, an exhaust nut and gasket, and four locating pins add listed fitting hardware that can help complete the assembly work without sourcing those particular items separately.
- 50mm bore for the stated GY6 50cc-to-100cc range
- Includes cylinder head and cylinder block assembly
- 69mm valve length is clearly specified
- Lists intake and exhaust screws, exhaust hardware, and four locating pins
- The 69mm valve length excludes 64mm-valve configurations.
Skip it if you have 64mm valves; the matching ZTDZZH 64mm-valve kit B0B1KZL16J is the listed alternative.
This is a suitable choice for a 139QA or 139QMB project needing a 50mm block and 69mm-valve head assembly. Its included locating pins and exhaust hardware are useful details, but valve length sets the fit boundary.
Full product details
| Brand | ZTDZZH |
|---|---|
| Item Weight | 4.4 pounds |
| Item model number | 50 |
| Manufacturer | HY |
| Part Number | 50 |
| Model | TG-100 |
| Package Dimensions | 6.61 x 6.18 x 6.02 inches |
Listed on Amazon as: 50mm Bore Cylinder Head Kit for GY6 50cc to 100cc Engine with 69mm Valves scooter taotao kazuma ATV Moped
View on Amazon#6
6. ZTDZZH 64mm Valve Head Kit
- Weight: 4.33 lb
- Package Dimensions: 6.26 x 6.14 x 5.98 in
Best for: 64mm-valve GY6 top end.
Why it ranks #6: This 50mm cylinder and head kit specifies 64mm valves for 139QA/139QMB engines, making it useful when that shorter valve length matches.
The 64mm valve length is the defining fit detail of this ZTDZZH 50mm-bore head kit, which is explicitly not the 69mm version. It serves a GY6 139QA or 139QMB rebuild where that shorter valve configuration is required.
ZTDZZH lists a cylinder head and cylinder block assembly for a 50cc-to-100cc GY6 engine, with a 50mm bore. That pairing provides the core top-end assemblies for the stated upgrade range, while the 64mm valve length helps distinguish it from similar 69mm kits. The listed contents are limited to the head and block assembly, so buyers can plan separately for other rebuild pieces rather than assuming they are included.
- 50mm bore for the stated GY6 50cc-to-100cc range
- Includes cylinder head and cylinder block assembly
- 64mm valve length is clearly specified
- Identifies 139QA and 139QMB engine applications
- The kit lists only the head and cylinder block assembly as included components.
Skip it if you need 69mm valves or a package that lists exhaust hardware and locating pins; this kit specifies 64mm valves.
Choose this for a compatible 139QA or 139QMB project specifically using 64mm valves and needing the head and block assemblies. Its contents are focused, so plan for any additional parts required by the rebuild.
Full product details
| Brand | Generic |
|---|---|
| Item Weight | 4.33 pounds |
| Manufacturer | AH |
| Part Number | TG-64 |
| Package Dimensions | 6.26 x 6.14 x 5.98 inches |
Listed on Amazon as: ZTDZZH 50mm Bore Cylinder Head Kit for GY6 50cc to 100cc Engine with 64mm Valves scooter taotao kazuma ATV Moped
View on Amazon#7
7. GOOFIT 64mm Valve Kit
- Weight: 5.15 lb
- Package Dimensions: 11.02 x 8.31 x 4.06 in
Best for: 64mm-valve 50cc rebuild.
Why it ranks #7: The kit is specifically for GY6 4-stroke 49cc/50cc 139QMB and 1P39QMB engines, but its 64mm valve length excludes 69mm setups.
GOOFIT specifies a 64mm valve length and limits this kit to GY6 four-stroke 49cc and 50cc 139QMB or 1P39QMB engines. That narrow application suits a matching 50cc rebuild rather than a 69mm-valve conversion or a stated 100cc kit.
The explicit 64mm valve specification separates this kit from 69mm-head options, while its stated engine applications identify the intended GY6 49cc and 50cc four-stroke use. GOOFIT describes the metal components as wear resistant and tolerant of high temperatures, and says core parts are precision machined for stable performance under high-speed, high-pressure conditions. Those material and machining claims speak to operating demands, but the listed fit remains limited to the named engine types.
- 64mm valve length is clearly specified
- Listed for GY6 four-stroke 49cc and 50cc engines
- Names 139QMB and 1P39QMB applications
- Describes metal components as wear resistant and heat tolerant
- The listing limits use to 49cc and 50cc engines, not a stated 100cc upgrade.
Skip it if you need 69mm valves or a listed 50mm 100cc conversion rather than this 64mm-valve 49cc or 50cc kit.
This suits an owner rebuilding a listed 49cc or 50cc GY6 four-stroke with 64mm valves. The specified engine codes and valve length are important boundaries; it is not presented as a 100cc conversion kit.
Full product details
| Brand | GOOFIT |
|---|---|
| Item Weight | 5.15 pounds |
| Item model number | Group-11 |
| Manufacturer | GOOFIT |
| Part Number | Group-11 |
| Package Dimensions | 11.02 x 8.31 x 4.06 inches |
Listed on Amazon as: GOOFIT Big Bore Cylinder Rebuild Kit for GY6 50cc 139QMB Racing Scooter Parts 64mm Valve
View on Amazon#8
8. HANQIMOTO 69mm Head Kit
- Weight: 4.67 lb
- Package Dimensions: 12.99 x 8.07 x 5.51 in
Best for: 12.77mm-pin 69mm head kit.
Why it ranks #8: This 50mm kit lists 69mm valves for 139QMB/139QMI engines and provides valve diameters and a 12.77mm wrist-pin specification.
HANQIMOTO specifies a 12.77mm wrist-pin outside diameter alongside its 50mm cylinder and 69mm head assembly. Those concrete dimensions make this kit relevant to a GY6 139QMA or 139QMB 50cc-to-100cc rebuild where the listed measurements match the project.
The kit is listed for 69mm, four-stroke 139QMB or 139QMI engines, with a 50mm cylinder diameter and intake and exhaust valve outside diameters of 18mm and 16mm. These measurements give a buyer several fit details to compare against the engine parts being replaced. The manufacturer also describes the components as high-strength, corrosion-resistant, and durable, and claims heat dissipation and oil-saving benefits; those are stated product claims, not additional included parts.
- 50mm cylinder diameter for a stated 50cc-to-100cc kit
- 69mm head assembly for listed four-stroke GY6 applications
- Specifies 18mm intake and 16mm exhaust valve outside diameters
- Lists a 12.77mm wrist-pin outside diameter
- The listed 69mm valve configuration is not the 64mm version.
Skip it if you need a 64mm-valve head or your rebuild requires a package listing additional ignition and oil-pump parts.
This fits a buyer comparing exact dimensions for a 139QMA or 139QMB 50mm-bore rebuild, especially the 69mm head and 12.77mm pin. Check those measurements against the engine configuration before choosing this assembly.
Full product details
| Brand | HANQIMOTO |
|---|---|
| Item Weight | 4.67 pounds |
| Item model number | GY6-80 50mm |
| Manufacturer | HANQIMOTO |
| Part Number | GY6-80 50mm |
| Model | GY6-80 50mm |
| Package Dimensions | 12.99 x 8.07 x 5.51 inches |
Listed on Amazon as: 50mm Big Bore Cylinder Head Kit Assy with 69mm Valves for GY6 50cc-100cc
View on Amazon#9 · 47mm Bore Option
9. TRKIMAL 80cc Cylinder Kit
Best for: 47mm 80cc engine upgrade.
Why it ranks #9: Its 47mm bore is described as an upgrade from 50cc to 80cc and the kit includes a piston, rings, pin, gaskets, and intake and exhaust studs.
The 47mm cylinder is the defining choice in TRKIMAL’s kit, which is specified to take a GY6 49cc or 50cc engine to 80cc. It suits a buyer seeking that smaller displacement step rather than a 50mm 100cc rebuild package.
This kit includes the cylinder, piston, rings, pin, and pin clip, giving the core reciprocating parts for the stated 80cc conversion. Its 13mm piston-pin outside diameter is a specific measurement to account for during a rebuild. Valve oil seal, gaskets, tensioner and exhaust gaskets, intake and exhaust studs, and an exhaust nut are also listed, so the package covers several related replacement pieces alongside the cylinder assembly.
- 47mm cylinder for a stated 50cc-to-80cc upgrade
- Includes piston, rings, pin, and pin clip
- Lists valve oil seal and multiple gaskets
- Includes intake and exhaust studs and exhaust nut
- This 47mm kit is an 80cc upgrade, not a 50mm 100cc conversion.
Skip it if you want a 50mm 100cc conversion; Glixal’s B01303YV08 kit is listed with a 50mm bore and 100cc upgrade.
This suits a GY6 49cc or 50cc owner choosing a 47mm, 80cc rebuild with related gaskets and hardware included. Keep the 13mm piston-pin measurement and the smaller displacement step in view when selecting parts.
Full product details
| Brand | TRKIMAL |
|---|---|
| Manufacturer | TRKIMAL |
| Model | TRKIMAL-00030-1 |
Listed on Amazon as: Performance Upgrade Big Bore Cylinder Kit GY6 80cc 47mm for GY6 49cc 50cc 139QMB ATV Scooter Moped Go Kart
View on Amazon#10
10. Chanoc 80cc Cylinder Kit
- Weight: 2.15 lb
- Package Dimensions: 5.39 x 4.69 x 3.5 in
Best for: 47mm hill-climb upgrade.
Why it ranks #10: This 47mm kit is listed for 139QMA/139QMB engines, but provides a narrower cylinder-kit set than the higher-ranked comprehensive 50mm options.
Chanoc’s 47mm cylinder kit is stated to take a GY6 49cc or 50cc engine to 80cc, with the listing specifically noting easier hill climbing. It suits a 139QMA or 139QMB owner seeking that displacement step rather than a 50mm 100cc conversion.
The 47mm bore and 13mm piston-pin outside diameter are the key specifications for this kit, which is described for four-stroke GY6 50, 139QMA, and 139QMB engines. The seller states that the upgrade adds power and makes climbing hills easier, giving the conversion a practical use case. Compatibility also names several Chinese-import ATV, scooter, and moped brands, including TaoTao, Sunl, BMS, Roketa, Kazuma, Baotian, and Jonway.
- 47mm bore for a stated 50cc-to-80cc upgrade
- Lists compatibility with 139QMA and 139QMB engines
- 13mm piston-pin outside diameter is specified
- Seller states the upgrade adds power for easier hill climbing
- This 47mm kit is an 80cc upgrade, not a 50mm 100cc kit.
Skip it if you want a 50mm 100cc conversion; Glixal’s B01303YV08 listing specifies that larger bore and upgrade.
Choose this for a compatible 139QMA or 139QMB owner seeking a 47mm 80cc upgrade and the listed hill-climbing benefit. Its 13mm pin dimension and smaller displacement step are the main selection boundaries.
Full product details
| Brand | Chanoc |
|---|---|
| Item Weight | 2.15 pounds |
| Item model number | BG50-GY80 |
| Manufacturer | Chanoc |
| Part Number | BG50-GY80 |
| Package Dimensions | 5.39 x 4.69 x 3.5 inches |
Listed on Amazon as: 80cc Big Bore 47mm Cylinder Rebuild Kit for GY6 49cc 50cc ATV Scooter Moped with 139QMA 139QMB Engine
View on AmazonThe 64mm vs 69mm valve-length trap
Valve length is a compatibility trap: a 64mm head and a 69mm head are not interchangeable just because both listings mention a 50mm bore. ZTDZZH 64mm Valve Head Kit explicitly says it is not for 69mm valves, while ZTDZZH 69mm Valve Head Kit identifies the opposite length. Glixal 100cc Large-Valve Kit is described for 69mm long-valve-style heads and warns that owners with a 64mm original head must change rocker arms to the ones in its kit.
Before ordering, identify the engine and measure or verify the existing head’s valve length; do not infer it from scooter make or displacement. A wrong-length head can make the otherwise suitable bore kit unusable without additional compatible parts.
The listings do not establish a universal fit across all GY6 variations, so compare the kit description with the actual engine and existing head.
Bore size, displacement claims, and kit scope
A 50mm bore is the listed size for the products described as 100cc upgrades, while 47mm options are described as upgrades to 80cc. Those descriptions are product claims, not a guarantee of a particular finished displacement or performance on every engine. Kit scope also changes what you need to source separately: KYMLAA 100cc Big Bore Kit and TRKIMAL 100cc Big Bore Kit list a camshaft, oil pump, CDI, ignition coil, and other components, whereas Glixal 100cc Cylinder Kit lists the cylinder, piston, rings, pin, and gaskets.
The bare-cylinder approach may suit someone replacing specific top-end parts; a broader bundle may suit someone seeking more of the associated components in one package. Still, do not assume every listed part is needed or compatible with your setup.
Check the included-parts list and engine configuration before treating a package as a complete installation solution.
How to Choose a GY6 Big Bore Kit
Bore and stated upgrade size
Choose the bore based on the upgrade described for your engine and the parts you want to replace. The 50mm kits are presented as 100cc upgrades, including KYMLAA 100cc Big Bore Kit, while the TRKIMAL 80cc Cylinder Kit and Chanoc 80cc Cylinder Kit use a 47mm bore and are described as upgrades to 80cc. Glixal 100cc Cylinder Kit also specifies a 50mm inner cylinder diameter and 13mm piston pin.
Buyers seeking the larger listed upgrade should compare 50mm options; those wanting the 47mm configuration can consider the 80cc listings. Verify the engine’s existing setup and kit fitment rather than selecting by the scooter’s original 50cc label alone.
Valve length and head configuration
Match the kit’s valve length to your existing head before buying. Several products distinguish 64mm from 69mm: ZTDZZH 64mm Valve Head Kit specifies 64mm and says it is not 69mm, while ZTDZZH 69mm Valve Head Kit specifies 69mm and says it is not 64mm. KYMLAA 100cc Big Bore Kit and TRKIMAL 100cc Big Bore Kit are listed in 69mm valve-length versions.
Glixal 100cc Large-Valve Kit adds 18.5/20.5mm valves and cautions that a 64mm original head requires different rocker arms. A buyer with verified 69mm hardware should focus on those listings; one with 64mm hardware should choose a matching kit and confirm any associated parts.
Included parts and engine compatibility
Check both the engine code and the included parts list, because these kits vary from cylinder-only sets to broader rebuild packages. KYMLAA 100cc Big Bore Kit lists cylinder and head kits, camshaft, gaskets, oil pump and gear, CDI, coil, and spark plug; Glixal 100cc Cylinder Kit lists a cylinder, piston, rings, pin, seals, and gaskets. HANQIMOTO 69mm Head Kit identifies 139QMB or 139QMI engines and a 12.77mm wrist pin, while Glixal 100cc Cylinder Kit specifies a GY6 139QMB 4-stroke engine.
Buyers replacing top-end components may prefer a narrower kit if it matches their needs; those seeking more bundled components should compare the broader lists. Confirm exact fitment for your engine before ordering.
Which Big Bore Kit Should You Choose?
For a compatible GY6 139QMB scooter and a broad parts bundle, choose KYMLAA 100cc Big Bore Kit: it lists a 50mm bore, 69mm valve-length version, and multiple engine components. If you want a similar bundle, TRKIMAL 100cc Big Bore Kit also specifies a 69mm version and includes a camshaft, oil pump, CDI, and coil. Choose Glixal 100cc Large-Valve Kit if its 18.5/20.5mm valves suit your setup and you have checked the rocker-arm note.
For a simpler 50mm cylinder set, consider Glixal 100cc Cylinder Kit after confirming 139QMB fitment. If your existing head is 64mm, compare ZTDZZH 64mm Valve Head Kit or GOOFIT 64mm Valve Kit.
For a 47mm, 80cc-described option, consider TRKIMAL 80cc Cylinder Kit.
Related Buying Guides
Frequently Asked Questions
How can I identify whether my scooter has a 139QMB or 139QMA engine?
Check the engine code stamped or marked on the engine, and compare it with the scooter’s documentation or the seller’s fitment information. Do not rely on the scooter’s advertised displacement alone. If the code is unclear, have a mechanic identify it before ordering; listed fitment examples do not guarantee compatibility with your particular engine.
How do I measure valve length and confirm whether my head uses 64mm or 69mm valves?
Measure each valve from end to end after removing it from the cylinder head, then compare the result with the kit’s stated 64mm or 69mm valve option. Confirm the measurement against the existing head and its parts before ordering. If you are unsure how to remove or measure valves, ask a mechanic to check them.
What other parts or tuning may be needed after installing a GY6 big bore kit?
The parts needed depend on the kit and your engine’s current setup. Check exactly what the kit includes, then confirm any required supporting parts and tuning with its instructions or a mechanic. These listings vary: some describe bundles with components such as a camshaft, oil pump, CDI, coil, or spark plug, while others describe cylinder or head kits.
Can a 50cc scooter use any of these kits?
No. These listings describe kits for specific GY6 engine codes and configurations, including 139QMB and 139QMA, rather than every 50cc scooter. Confirm your engine code, valve length, and existing head configuration against the kit details before ordering.
The stated fitment examples are a starting point, not a substitute for checking your engine.
How should I choose between a 64mm and 69mm valve kit?
Choose based on the valve length that matches your existing cylinder head and the kit’s stated configuration. The listings include both 64mm and 69mm options, so do not select by displacement description alone. Measure your valves or have the head checked, and review any additional fitment notes before deciding.
Final Words
For a compatible GY6 139QMB scooter, the KYMLAA 100cc kit is the leading choice if you want a broad bundle and have confirmed the 50mm bore and 69mm valve-length version suit your engine. TRKIMAL is another bundled option; Glixal’s large-valve kit requires checking its valve sizes and rocker-arm note. For simpler cylinder or head kits, match the stated 50mm or 47mm bore and 64mm or 69mm valves to your existing parts before ordering.
