Glixal GY6 100cc Big Bore Cylinder Rebuild Kit — 69mm Cylinder with 18.5/20.5mm Big-Valve Head, DLC Rings

Glixal's GY6 100cc Complete Big Bore Cylinder Rebuild Kit is a drop-in performance rebuild set with a 69mm cylinder and large-valve head that upgrades 139QMB/139QMA/147QMD engines for stronger throttle response and higher top-end potential.

This rebuild kit replaces the stock cylinder and head components with a 69mm big-bore cylinder, a performance head fitted with 18.5mm intake and 20.5mm exhaust valves (compared to typical stock sizes), and DLC-coated rings designed to reduce friction and extend sleeve life. The package includes the necessary gaskets and hardware for a complete rebuild on compatible short-case GY6 engines and notes installation specifics so you get fitment and function right first time.

Will this kit fit my 139QMB/139QMA/147QMD engine?

The kit targets GY6-style 139QMB, 139QMA, and 147QMD engines that accept a 69mm long-valve head configuration. It is intended for short-case (8-bolt) engines as shipped; check your current head valve length and rocker arms before installation.

• Designed for 69mm long-valve heads; not directly matched to 64mm valve heads.
• If your original head has 64mm valves, swap in the kit's rocker arms as instructed.
• Includes short-case (8-bolt) engine side cover gasket—confirm case type.

How do the larger valves and big-bore cylinder change performance?

Larger valves and a 69mm cylinder increase air-fuel flow capability, which improves midrange punch and top-end potential when combined with correct jetting and tuning. The bigger valve diameters (18.5/20.5mm) let more mixture into and exhaust out of the combustion chamber relative to many stock setups.

• 18.5mm intake and 20.5mm exhaust valves for increased flow over stock sizes.
• Bore increase to 69mm adds displacement and torque potential.
• Best results achieved with matching carburetor tuning and ignition timing adjustments.

What materials and components are included for durability?

The kit includes DLC-coated piston rings and a performance head assembly to reduce wear and extend component life under higher loads. The DLC (diamond-like carbon) coating lowers friction against the cylinder sleeve for improved wear resistance.

• DLC wear-resistant piston rings to reduce friction and protect the sleeve.
• Performance big-valve cylinder head assembly with upgraded valve sizes.
• Gaskets and hardware appropriate for short-case 8-bolt engines included.

Are there any important installation notes I should know?

Follow the kit's orientation details exactly: the AT marking on the piston must face outward and the 6mm small hole must point up or away from the motor. Verify head valve length and, if necessary, swap rocker arms when converting from 64mm setups.

• AT marking faces the piston outward; 6mm hole must point up/away from the motor.
• Change rocker arms if original head uses 64mm valve length.
• Confirm your case is the short-case (8-bolt) style for included gasket compatibility.

Who is this for: This Glixal GY6 100cc big bore rebuild kit is aimed at riders and DIY mechanics upgrading scooters, mopeds, ATVs, or go-karts powered by 139QMB/139QMA/147QMD engines who want increased displacement and airflow for stronger performance. It’s best suited for users comfortable with engine assembly and tuning, or for shops performing performance rebuilds; double-check valve lengths, rocker arm compatibility, and case style before purchasing.