This cylinder kit fits ZONGSHEN NX250 (engine code ZS178MM-2) 250cc 4-stroke water-cooled single-cylinder 4-valve dirt bikes, standard bore 78mm. Compatible with models from 2021–2025. Made of high-strength aluminum alloy with cast iron sleeve for durability and excellent heat dissipation. The kit includes cylinder block, piston, piston rings, piston pin, circlips and full top-end gasket set. It solves common issues like power loss, compression leakage and overheating, ideal for direct replacement and engine overhaul.