Best Big Bore Kit For 50Cc Scooter: Compare 10 GY6 Kits

#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: 69mm-valve complete upgrade.

Why it ranks #1: Its 50mm bore and 69mm valve-length head suit a substantial GY6 upgrade, and the listed kit adds camshaft parts, oil pump, gaskets, CDI, coil, and rollers.

A broad parts bundle—including camshaft, oil pump and gear, 6-pin racing CDI, and ignition coil—makes this KYMLAA kit more than a cylinder swap. Its 50mm bore and 69mm valve-length configuration target upgrades from 50cc, 60cc, or 80cc GY6 engines to 100cc, without EGR.

The included cylinder and head kits are accompanied by camshaft and seat, gaskets, oil-pump components, spring sets, copper rollers, CDI, ignition coil, and a three-electrode spark plug. That spread can reduce the need to source these listed upgrade parts separately during a rebuild. Fit remains specific: it is the 69mm valve version for applicable 139QMB engines, and the product lists examples including Jonway, Agility, People S50 4T, and Baotian models.

Skip it if you need 64mm valves for your GY6; the TRKIMAL 100cc 64mm-valve kit lists a similar broad component set.

Pick this for a compatible 139QMB build where the 69mm valve length and wide component bundle match the engine plan. Check the listed model examples and valve specification before assembling the upgrade.

Listed on Amazon as: GY6 Cylinder Rebuild Kits Kymlaa 100cc Big Bore Kit for 69mm Valve 49CC 50CC 139QMB Moped Scooter Engine 50mm Bore Upgrade Set with 6pin Racing CDI Ignition Coil Performance Spark Plug Clutch Spring

#2 · Best 64mm Valve Kit

2. TRKIMAL 100cc Big Bore Kit

• Weight: 6.6 lb
• Package Dimensions: 10.24 x 7.32 x 6.02 in

Best for: 64mm-valve 100cc conversion.

Why it ranks #2: This 50mm 100cc-oriented kit specifies a 64mm valve length and includes camshaft parts, oil pump and gear, CDI, ignition coil, spark plug, and rollers.

A 50mm bore with a 64mm valve-length head gives this TRKIMAL kit a specific route to a stated 100cc GY6 upgrade without EGR. It bundles camshaft parts, oil-pump gears, clutch springs, copper rollers, and ignition components alongside the cylinder and head.

The cylinder body and head kits form the core, while the camshaft and seat, gasket set, and oil pump and gear add rebuild components that can simplify sourcing. Clutch spring sets and copper rollers bring transmission-related parts into the same package. Its 64mm valve version is distinct from 69mm-head kits, and the listed fit examples include Jonway, Agility, People S50 4T, and Baotian scooters.

Skip it if you need a 69mm-valve head; the KYMLAA 100cc kit specifies that valve length with a similar broad component set.

Choose this for a compatible no-EGR GY6 build requiring a 50mm bore and 64mm valve head, especially when the listed engine components are useful. Check valve length and scooter application before installation.

Listed on Amazon as: GY6 Cylinder Rebuild Kits Trkimal 100cc Big Bore Kit for 64mm Valve 49CC 50CC 139QMB Moped Scooter Engine 50mm Bore Upgrade Set with 6pin Racing CDI Ignition Coil Performance Spark Plug Clutch Spring

#3 · Broadest Component Set

3. GOIRTUTSS 100cc Rebuild Kit

• Weight: 7.24 lb
• Package Dimensions: 10.47 x 7.6 x 6.06 in

Best for: 69mm-valve 100cc bundle.

Why it ranks #3: The 50mm kit lists a 69mm valve head, camshaft, oil pump and gears, rollers, CDI, coil, and spark plug for compatible GY6 49cc and 50cc engines.

A 50mm cylinder body and 69mm-valve head anchor this GOIRTUTSS kit’s stated upgrade from 50cc, 60cc, or 80cc GY6 engines to 100cc. It combines those core parts with a camshaft, oil-pump components, rollers, and ignition pieces for a broad rebuild package.

The camshaft and seat, full gasket set, oil pump and gears, spring set, and pure copper roller assembly extend the package beyond the cylinder and head. A 6-pin racing AC CDI, ignition coil, and three-electrode spark plug add listed ignition parts, reducing separate sourcing for those components. The kit is specified for GY6 49CC, 50CC, and 139QMB engines without an EGR system, so that system detail matters when choosing it.

Skip it if you have an EGR-equipped engine; the KYMLAA 69mm kit also specifies a no-EGR application, so seek an EGR-compatible option.

This fits buyers planning a 100cc-style GY6 rebuild who need the 69mm valve setup and a broad set of listed engine components. Its no-EGR requirement is a critical compatibility boundary.

Listed on Amazon as: 69mm Cylinder Rebuild Kit for GY6 100cc 49-50cc Scooter Engine

#4 · Largest Valves

4. Glixal 100cc Large-Valve Kit

• Weight: 8.34 lb
• Package Dimensions: 16.5 x 12.05 x 4.09 in

Best for: Large-valve 100cc rebuild.

Why it ranks #4: Its 50mm cylinder kit includes 18.5/20.5mm valves, larger than the stated stock 16/18.5mm, plus CDI and ignition components; head compatibility needs careful checking.

An 18.5/20.5mm large-valve head sets this Glixal kit apart from stock 16/18.5mm valves, pairing a 50mm cylinder and piston with a complete GY6 rebuild package. It targets 139QMB, 139QMA, and 147QMD engines, with the larger head intended to support a 100cc setup.

The 69mm long-valve head is the key fit detail: scooters with a 64mm original head need the included rocker arms changed, while the kit is specified for 69mm-style heads. DLC-coated piston rings are described as wear-resistant and friction-reducing, supporting cylinder protection in operation. Alongside the cylinder, piston and head, the package includes a racing AC CDI, ignition coil, spark plugs, studs, bolts, and exhaust gasket, consolidating several rebuild components.

Skip it if you have a 64mm-valve head and want a matching package; the ZTDZZH 50mm kit specifies 64mm valves.

Choose this for a 139QMB, 139QMA, or 147QMD rebuild where a 50mm cylinder and larger 69mm-style valve head are appropriate. Check the original head and rocker-arm arrangement before starting installation.

Listed on Amazon as: Glixal GY6 100cc 50mm Complete Big Bore Cylinder Rebuild Kit with Performance Big Valve Cylinder Head Assy for 139QMB 139QMA 147QMD Engine Scooter Moped ATV Go-Kart (69mm-18.5/20.5mm Larger Valves)

#5

5. hauertzx 50mm Rebuild Kit

• Weight: 5.94 lb
• Package Dimensions: 10.24 x 7.28 x 5.91 in

Best for: 69mm valve with A9 crankshaft.

Why it ranks #5: This 50mm kit lists a 69mm valve head and A9 crankshaft, CDI, coil, spark plug, and 6.5g copper roller, with compatibility claimed for many Chinese 139QMB and 139QMA scooters.

An A9 crankshaft joins this 50mm, 69mm-valve rebuild kit, giving compatible 139QMB or 139QMA owners a broader engine-parts package for a GY6 upgrade. The listed contents also include a 1500RPM clutch spring, high-performance CDI, ignition coil, spark plug, and 6.5g copper roller.

The 50mm cylinder and piston set the core upgrade, while the 69mm valve specification identifies the head configuration to match. An A9 crankshaft, 1500RPM clutch spring, and 6.5g copper roller add drivetrain-related parts to the package; the CDI, coil, and spark plug address ignition components. The product lists many Chinese 49cc and 50cc scooter, moped, and ATV applications equipped with 139QMB or 139QMA four-stroke engines, so those engine codes are central to fit selection.

Skip it if you need a 64mm-valve 47mm upgrade; the TRKIMAL 80cc kit specifies that bore and valve length.

Consider this package for a compatible 139QMB or 139QMA build needing the 50mm, 69mm-valve configuration and listed crankshaft and ignition parts. Confirm the engine code and valve arrangement before installation.

Listed on Amazon as: High Performance 50mm Big Bore Cylinder Rebuild Kit with 69mm Valves Cylinder Head Assy CDI Ignition Coil Spark Plug for 139QMB 139QMA Engine Scooter Moped ATV Go-Kart (69mm upgrade valve)

#6

6. TRKIMAL 47mm 80cc Kit

• Weight: 9.38 lb
• Package Dimensions: 11.3 x 7.8 x 6.8 in

Best for: 64mm-valve 80cc package.

Why it ranks #6: The 47mm cylinder and 64mm valve head offer a smaller 80cc-oriented step, with a gasket set, CDI, coil, regulator, relay, spark plug, and intake manifold.

A 47mm bore paired with a 64mm-valve head makes this TRKIMAL kit a clearly specified 80cc upgrade route for GY6 49cc, 50cc, 60cc, or 80cc engines. Its parts list extends beyond the cylinder to include ignition, charging, relay, manifold, and roller components.

The cylinder block, piston assembly, rings, wrist pin, head, and full gasket set cover the core rebuild, with the 64mm valve length marking the head version. A 6-pin CDI, ignition coil, 4-pin AC regulator, relay, and A7TC spark plug add electrical components to the package. Intake manifold and muffler bolts, plus 8.5g rollers, are also listed, helping buyers source several installation and CVT-related parts together.

Skip it if you want a 100cc conversion; the TRKIMAL 64mm-valve 100cc kit specifies a 50mm bore.

Choose this for a GY6 owner whose plan calls for a 47mm, 64mm-valve 80cc package with electrical and mounting parts. Verify the valve length and listed engine application before work begins.

Listed on Amazon as: GY6 Cylinder Rebuild Kits Trkimal 47mm 80cc Big Bore Upgrade Kits for 49cc 50cc 139QMB Engines 64mm Valve scooter moped parts, GY6 Engine parts for Chinese Scooter(64mm Valve Length)

#7

7. ZTDZZH 50mm Cylinder Head Kit

• Weight: 4.33 lb
• Package Dimensions: 6.26 x 6.14 x 5.98 in

Best for: 64mm-valve head replacement.

Why it ranks #7: It specifies a 50mm bore and 64mm valves for GY6 50cc-to-100cc engines, but the stated included parts are limited to the cylinder head and cylinder block assembly.

A specified 64mm valve length distinguishes this 50mm-bore ZTDZZH kit from long-valve alternatives, giving GY6 139QA and 139QMB owners a cylinder head and block assembly in one package. Its stated application spans 50cc to 100cc engines, including scooters, mopeds, and ATVs.

The 50mm bore and 64mm valve length provide the essential fit specifications for buyers matching a GY6 engine’s cylinder and head arrangement. Because the listed contents are a cylinder head and cylinder block assembly, the kit centers on those two major components rather than presenting a broad ignition or gasket package. Checking the supplied product description and images before purchase is specifically advised, helping buyers assess the included parts and application before planning the rebuild.

Skip it if you need a broad rebuild bundle with ignition and valvetrain parts; the KYMLAA 69mm kit lists those components.

This suits a GY6 owner seeking a 50mm cylinder and 64mm-valve head assembly for a scooter, moped, or ATV. Its listed contents are narrow, so plan separately for any other rebuild components you need.

Listed on Amazon as: ZTDZZH 50mm Bore Cylinder Head Kit for GY6 50cc to 100cc Engine with 64mm Valves scooter taotao kazuma ATV Moped

#8

8. Glixal 47mm 80cc Kit

Best for: Simple 47mm cylinder refresh.

Why it ranks #8: This 47mm kit is listed for GY6 49cc, 50cc, 60cc, and 80cc engines and supplies the cylinder, piston, rings, pin, gaskets, and intake and exhaust studs.

A 47mm cylinder and 13mm piston pin define this Glixal kit’s compact approach to upgrading a GY6 49cc or 50cc engine toward an 80cc setup. It focuses on core cylinder-rebuild parts, including durable piston rings, rather than adding a head or ignition system.

The cylinder, piston, rings, pin, clips, valve oil seal, and gaskets cover key wear and sealing components for a cylinder rebuild. Intake and exhaust studs, an exhaust nut, and exhaust gasket are also listed, helping address related mounting needs during installation. Its 47mm bore is specified for GY6 49cc, 50cc, 60cc, and 80cc engines; the listed 13mm piston-pin diameter is another important compatibility detail to check against the existing setup.

Skip it if you want a head and ignition bundle in one purchase; the TRKIMAL 47mm kit includes a 64mm-valve head and electrical parts.

This is a focused option for a GY6 owner refreshing cylinder internals with a 47mm bore and 13mm piston pin. It makes most sense when the existing head and ignition components are being retained.

Listed on Amazon as: Glixal ATMT1-008 GY6 80cc 47mm High Performance Big Bore Cylinder Kit

#9

9. Maoyubelt 47mm Big Bore Kit

• Weight: 1.76 lb
• Package Dimensions: 6.49 x 5.7 x 4.7 in

Best for: Core 47mm cylinder parts.

Why it ranks #9: It offers a 47mm cylinder, piston, rings, pin, clips, gaskets, and valve oil seals for GY6 139QMB applications, but lists fewer supporting upgrade components.

A 47mm cylinder block and a 1.76-pound listed package make this Maoyubelt kit a compact, core-parts option for a GY6 50cc-to-80cc rebuild. It focuses on the cylinder, piston, rings, pin, clips, head gaskets, and valve oil seals rather than a complete engine bundle.

The cylinder block, piston, complete ring set, circlips, and piston pin cover the main bore-and-piston components, while two head-gasket sets and two valve oil seals add sealing parts for the rebuild. The kit is listed for GY6 or 139QMB engine clones in scooters, go-karts, ATVs, and buggies. Since the contents center on these parts, buyers can retain or source other engine components separately as their repair requires.

Skip it if you need a head and ignition package included; the TRKIMAL 47mm 80cc kit lists a 64mm-valve head and electrical parts.

This suits a GY6 or 139QMB owner replacing core cylinder and piston parts for a 47mm setup across a scooter, ATV, or kart. It is not a whole-engine rebuild bundle, so plan around that scope.

Listed on Amazon as: 47mm Big Bore Kit GY6 50cc to 80cc Scooter Moped 139 QMB 139QMB Cylinder Piston Rings

#10

10. XMT-MOTO 50cc-to-80cc Kit

• Weight: 6.07 lb
• Package Dimensions: 12.6 x 7.87 x 6.69 in

Best for: Wide Chinese-scooter fit list.

Why it ranks #10: The listing names compatible 49cc and 50cc four-stroke scooters and an 80cc upgrade, but provides less precise bore, valve-length, and included-component detail than the other choices.

A long compatibility list across Roketa, Taotao, SUNL, Jonway, and Baja models is the main draw of this XMT-MOTO aluminum 50cc-to-80cc bore kit. It is an aftermarket cylinder component set for 49cc and 50cc four-stroke scooters, with fitment examples spanning several model families.

The broad model list can help owners of named scooter families identify a possible application, while the stated 50cc-to-80cc GY6 use frames the upgrade. Aluminum construction is specified for the aftermarket components, and the description says the parts are new and in good working condition. Installation instructions are not included, so owners should plan their own service procedure rather than relying on package guidance for assembly.

Skip it if you want a stated 47mm bore and a detailed gasket-and-piston contents list; the Maoyubelt 47mm kit provides those specifics.

This may suit an owner of a scooter in its extensive named compatibility list seeking a 50cc-to-80cc GY6 bore kit. Confirm the exact model match and plan installation without supplied instructions.

Listed on Amazon as: XMT-MOTO Scooter GY6 50CC To 80CC Big Bore Cylinder Fit for VIP Roketa Taotao Baja Silver