Restore top-end performance with the Namura NX-40025-BKA Top End Kit, designed for select Yamaha two-stroke motocross and cross-country motorcycles. This complete kit includes a piston, piston rings, wrist pin, retaining clips, top-end bearing, and gasket kit, providing the primary components needed for a dependable top-end rebuild. The ceramic-composite piston is designed for a 66.36 mm bore application with an 11:1 compression ratio and is suitable for compatible Yamaha YZ250 and YZ250X models.
Namura uses a hypereutectic casting process to increase silicon content, helping reduce expansion rates and improve wear resistance under elevated cylinder temperatures. The piston skirt features a rolled-on MOS2 coating made with Teflon and molybdenum. This bonding process is engineered to provide a stronger coating than conventional spray-on applications while reducing friction, improving heat transfer, and helping minimize the risk of cold seizures during operation.
The machined smooth piston head helps reflect combustion heat and reduce carbon buildup, supporting piston protection and consistent performance. An anodized dome further improves heat resistance and durability, while the included gaskets and top-end hardware help simplify installation. This Namura top-end kit fits 2016 and 2017 Yamaha YZ250X models, as well as Yamaha YZ250 models from 2002 through 2009. Confirm year, model, bore specification, and cylinder compatibility before installation.
Features:
- Complete top-end kit includes piston, rings, wrist pin, retaining clips, top-end bearing, and gasket kit
- 66.36 mm piston size with an 11:1 compression ratio for compatible Yamaha applications
- MOS2 Teflon and molybdenum-coated skirt helps reduce friction, improve heat transfer, and minimize cold-seizure risk
- Machined smooth head helps reflect combustion heat and reduce carbon buildup
- Anodized dome improves heat resistance and piston durability
- Hypereutectic casting process increases silicon content for reduced expansion and improved wear resistance
- Fits 2016-2017 Yamaha YZ250X and 2002-2009 Yamaha YZ250 models
- Brand: Namura
- Manufacturer part number: NX-40025-BKA
- Vendor part number: 185-4025BA
Fitment:
2002 Yamaha YZ250
2003 Yamaha YZ250
2004 Yamaha YZ250
2005 Yamaha YZ250
2006 Yamaha YZ250
2007 Yamaha YZ250
2008 Yamaha YZ250
2009 Yamaha YZ250
2010 Yamaha YZ250
2011 Yamaha YZ250
2012 Yamaha YZ250
2013 Yamaha YZ250
2014 Yamaha YZ250
2015 Yamaha YZ250
2016 Yamaha YZ250
2016 Yamaha YZ250X
2017 Yamaha YZ250
2017 Yamaha YZ250X
2018 Yamaha YZ250
2018 Yamaha YZ250X
2019 Yamaha YZ250
2019 Yamaha YZ250X
2020 Yamaha YZ250
2020 Yamaha YZ250X
2021 Yamaha YZ250
2021 Yamaha YZ250X
2022 Yamaha YZ250
2022 Yamaha YZ250X