The Namura NX-40000-CK Top End Kit is designed for select Yamaha YZ125 two-stroke applications requiring a 53.96 mm piston with approximately 11:1 compression. This complete ceramic-coated top-end assembly includes the piston, piston rings, wrist pin, retaining clips, top-end bearing, and gasket kit for a convenient rebuild solution. Manufacturer part number NX-40000-CK and vendor part number 185-4000C identify this Namura replacement kit.
The piston uses a MOS2, or Teflon and molybdenum, coated skirt applied through a rolled-on process intended to create a durable bond. This coating helps reduce friction, improve heat transfer, and minimize the risk of cold seizures during operation. The machined smooth head is designed to reflect combustion heat and help limit carbon buildup, supporting piston protection and consistent engine performance. The anodized dome adds heat resistance and durability, while the hypereutectic casting process provides increased silicon content for controlled expansion and enhanced wear resistance at elevated cylinder temperatures.
Fitment: This Namura top-end kit fits 1998 Yamaha YZ125, 1999 Yamaha YZ125, and 2000 Yamaha YZ125 models. Verify the existing cylinder bore, piston clearance, compression configuration, and engine application before installation. The kit is intended for top-end service and should be installed using the manufacturer’s recommended procedures, measurements, and torque specifications.
Features:
- Complete top-end kit includes piston, rings, wrist pin, retaining clips, top-end bearing, and gasket kit
- MOS2 Teflon and molybdenum coated skirt helps reduce friction, improve heat transfer, and minimize cold-seizure risk
- Machined smooth piston head helps reflect combustion heat and reduce carbon buildup
- Anodized piston dome improves heat resistance and durability
- Hypereutectic casting process provides controlled expansion and increased wear resistance
- 53.96 mm piston size with approximately 11:1 compression
- Fits 1998-2000 Yamaha YZ125 models
Fitment:
1998 Yamaha YZ125
1999 Yamaha YZ125
2000 Yamaha YZ125