Cylinder Kits & Big Bore Kits

Affordable big bore & standard cylinder kits (with piston, rings, pin, gaskets, often head/valves) for scooters, ATVs, pit bikes, go-karts, pocket bikes, and dirt bikes — boosts displacement/power (e.g., 50cc → 80cc, 150cc → 180cc-250cc), fixes scored cylinders, low compression, or smoking during rebuilds. Dominant sizes: 39mm-47mm (49cc-80cc GY6 139QMB), 52.4mm (110cc-125cc TaoTao/Lifan horizontal), 57.4mm (150cc GY6 152QMI/157QMJ), 44mm (2-stroke 47cc-54cc big bore), up to 63mm/64mm (180cc-250cc GY6) and outliers (89mm Honda XR400R, GX340/390 heads) — durable aluminum/steel kits for budget upgrades or repairs.

Best fits: GY6 4-stroke 49cc-250cc (139QMB/50cc short, 152QMI/157QMJ; TaoTao, SunL, Roketa, Baja, SSR, Coolster, Kazuma scooters/ATVs/go-karts), 2-stroke 43cc-50cc (Jog/Zuma/Vino, pocket bikes/mini quads, chain saws), horizontal engines 110cc-125cc (Lifan LF125, TaoTao/Coolster), YX140 140cc-150cc pit bikes, Honda CRF70/XR70/CT70/TRX70 + GX340/GX390, and many Chinese clones. Most are plug-and-play complete top-end kits (some with carb/spark plug/head/valves) for quick displacement boosts or full rebuilds!

Need only the cylinder head? Browse our Cylinder Heads collection.