For ZS CPS300 RBT Vortex250 74mm Big Bore Cylinder Piston Kit

  
This complete big bore top-end cylinder kit is designed for Zongshen CPS300, RBT250, Vortex250, and other 250-300cc 4-stroke single-cylinder engines. Engine specifications: 74.0 mm bore × 66.8-68.0 mm stroke, approx 287-293 cc displacement (upgraded from 250cc). Precise dimensions: Piston diameter 74.0 mm (big bore from OEM 70-72mm), piston rings 74 mm set (2 compression rings + 1 oil ring), piston pin 15-16 mm (verify before ordering).

Kit includes: 74mm cylinder block (cast iron or aluminum alloy), 74mm piston (forged or cast), piston rings, wrist pin, circlips, and full top-end gasket set (cylinder head gasket, base gasket, valve stem seals). Manufactured from high-strength aluminum alloy with durable cylinder bore plating for excellent heat dissipation, wear resistance, and reduced friction. Precision-machined piston with chrome-plated rings ensures reliable compression and consistent 4-stroke performance.

Replaces OEM Part Number References: 74mm big bore kit for 169FMM / 172FMM / 177FMM engine platforms. Compression Ratio Impact: Using stock head increases compression slightly - premium fuel recommended. Note: OEM standard bore for ZS NC250/CBB250 is 70-72mm. 74mm piston is a big bore performance upgrade - not standard size. Professional engine building experience strongly recommended.

Ideal for restoring lost power, reducing oil consumption, and performing complete top-end maintenance on 250-300cc single-cylinder engines. Perfect for off-road racing, enduro, dual-sport, and engine performance enthusiasts.