Restore reliable top-end performance with the NAMURA Top End Kit, manufacturer part number NA-40006-2K. This 83.5 mm, +0.50 mm oversize kit is designed for select Yamaha 400cc ATV applications and includes the essential components needed for a complete top-end rebuild. The kit includes a piston, piston rings, wrist pin, circlips, top-end bearing, and gasket kit.
Built for durability and consistent engine operation, the piston uses a hypereutectic casting process with increased silicon content. This construction helps reduce thermal expansion, improve wear resistance, and withstand higher cylinder temperatures. The 11:1 compression design supports strong combustion performance when used with the correct engine setup and fuel requirements.
The piston features MOS2, or Teflon/Molybdenum, coated skirts applied through a rolled-on process for a strong, durable bond. This coating helps reduce friction, improve heat transfer, and minimize the risk of cold seizures. Machined smooth heads help reflect combustion heat and reduce carbon buildup, while the anodized dome improves heat resistance and piston durability.
This NAMURA top-end kit fits 2000–2006 Yamaha YFM400FB Big Bear 4WD models with SRA suspension and 1993–1995 Yamaha YFM400FA Kodiak 4WD models with SRA suspension. Verify the model year, engine configuration, bore specification, and required oversize before installation. Manufacturer part number: NA-40006-2K. Vendor part number: 186-40062.
Features:
- Complete top-end kit: Includes piston, rings, wrist pin, circlips, top-end bearing, and gasket kit
- 83.5 mm bore size: +0.50 mm oversize specification for compatible Yamaha 400cc engine rebuilds
- 11:1 compression ratio: Designed to support strong combustion performance with compatible engine configurations
- MOS2-coated piston skirts: 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: Provides increased heat resistance and durability
- Hypereutectic construction: Increased silicon content helps reduce expansion and improve wear resistance
- Fitment: Fits 2000–2006 Yamaha YFM400FB Big Bear 4WD SRA and 1993–1995 Yamaha YFM400FA Kodiak 4WD SRA models
- Brand: NAMURA
- Manufacturer part number: NA-40006-2K
- Vendor part number: 186-40062
Fitment:
1993 Yamaha YFM400FA Kodiak 4WD [SRA]
1994 Yamaha YFM400FA Kodiak 4WD [SRA]
1995 Yamaha YFM400FA Kodiak 4WD [SRA]
1996 Yamaha YFM400FA Kodiak 4WD [SRA]
1997 Yamaha YFM400FA Kodiak 4WD [SRA]
1998 Yamaha YFM400FA Kodiak 4WD [SRA]
1999 Yamaha YFM400FA Kodiak 4WD [SRA]
2000 Yamaha YFM400 Big Bear 2WD [SRA]
2000 Yamaha YFM400FB Big Bear 4WD [SRA]
2001 Yamaha YFM400 Big Bear 2WD [SRA]
2001 Yamaha YFM400FB Big Bear 4WD [SRA]
2002 Yamaha YFM400 Big Bear 2WD [SRA]
2002 Yamaha YFM400FB Big Bear 4WD [SRA]
2003 Yamaha YFM400 Big Bear 2WD [SRA]
2003 Yamaha YFM400FB Big Bear 4WD [SRA]
2004 Yamaha YFM400 Big Bear 2WD [SRA]
2004 Yamaha YFM400FB Big Bear 4WD [SRA]
2005 Yamaha YFM400FB Big Bear 4WD [SRA]
2006 Yamaha YFM400FB Big Bear 4WD [SRA]
2007 Yamaha YFM400FBI Big Bear 4WD [IRS]
2008 Yamaha YFM400FBI Big Bear 4WD [IRS]
2009 Yamaha YFM400FBI Big Bear 4WD [IRS]
2010 Yamaha YFM400FBI Big Bear 4WD [IRS]