Restore top-end performance and dependability with the Namura NA-40015-6K Top End Kit. Designed for select Yamaha YFM250 models, this kit includes the essential components needed for a comprehensive piston replacement, including the piston, piston rings, wrist pin, retaining clips, top-end bearing, and gasket kit. The 72.45 mm piston size and 11:1 compression ratio are engineered for compatible Yamaha ATV applications.
The piston features MOS2, or Teflon and molybdenum, coated skirts applied through a rolled-on process that creates a strong bond. This coating helps improve heat transfer, reduce friction, and minimize the risk of cold seizures. Machined smooth heads help reflect combustion heat and reduce carbon buildup, supporting piston protection and efficient engine operation. Anodized domes add heat resistance and durability, while the hypereutectic casting process increases silicon content for controlled expansion and improved wear resistance under elevated cylinder temperatures.
Manufacturer and vendor part number: Namura NA-40015-6K. This top-end kit fits 2007-2009 Yamaha YFM250B Big Bear with SRA, 2005-2006 Yamaha YFM250B Bruin 2WD with SRA, and 1999-2003 Yamaha YFM250X Bear Tracker 2WD with SRA. Verify the model year, engine configuration, piston size, and required compression ratio before installation to ensure proper fitment.
Features:
- Complete top-end kit includes piston, piston rings, wrist pin, retaining clips, top-end bearing, and gasket kit
- 72.45 mm piston with an 11:1 compression ratio for compatible Yamaha YFM250 applications
- MOS2-coated piston skirts help reduce friction, improve heat transfer, and minimize cold-seizure risk
- Machined smooth piston heads help reflect combustion heat and reduce carbon buildup
- Anodized piston domes provide increased heat resistance and durability
- Hypereutectic casting process supports controlled expansion and enhanced wear resistance
- Fits 2007-2009 Yamaha YFM250B Big Bear SRA, 2005-2006 Yamaha YFM250B Bruin 2WD SRA, and 1999-2003 Yamaha YFM250X Bear Tracker 2WD SRA
Fitment:
1992 Yamaha YFB250 Timberwolf 2WD [SRA]
1993 Yamaha YFB250 Timberwolf 2WD [SRA]
1994 Yamaha YFB250 Timberwolf 2WD [SRA]
1994 Yamaha YFB250FW Timberwolf 4WD [SRA]
1995 Yamaha YFB250 Timberwolf 2WD [SRA]
1995 Yamaha YFB250FW Timberwolf 4WD [SRA]
1996 Yamaha YFB250 Timberwolf 2WD [SRA]
1996 Yamaha YFB250FW Timberwolf 4WD [SRA]
1997 Yamaha YFB250 Timberwolf 2WD [SRA]
1997 Yamaha YFB250FW Timberwolf 4WD [SRA]
1998 Yamaha YFB250 Timberwolf 2WD [SRA]
1998 Yamaha YFB250FW Timberwolf 4WD [SRA]
1999 Yamaha YFB250FW Timberwolf 4WD [SRA]
1999 Yamaha YFM250X Bear Tracker 2WD [SRA]
2000 Yamaha YFB250FW Timberwolf 4WD [SRA]
2000 Yamaha YFM250X Bear Tracker 2WD [SRA]
2001 Yamaha YFM250X Bear Tracker 2WD [SRA]
2002 Yamaha YFM250X Bear Tracker 2WD [SRA]
2003 Yamaha YFM250X Bear Tracker 2WD [SRA]
2004 Yamaha YFM250X Bear Tracker 2WD [SRA]
2005 Yamaha YFM250B Bruin 2WD [SRA]
2006 Yamaha YFM250B Bruin 2WD [SRA]
2007 Yamaha YFM250B Big Bear [SRA]
2008 Yamaha YFM250B Big Bear [SRA]
2009 Yamaha YFM250B Big Bear [SRA]