The NAMURA NA-10003-4K Top End Kit is designed for Honda sport ATV applications requiring an 85.97 mm +1.00 oversize piston with an 11:1 compression ratio. This complete high-compression top-end package includes a piston, piston rings, wrist pin, retaining clips, top-end bearing, and gasket kit for a comprehensive engine refresh.
Built using NAMURA’s hypereutectic casting process, the piston provides increased silicon content for reduced expansion, improved wear resistance, and dependable performance under elevated cylinder temperatures. The MOS2 Teflon/molybdenum-coated skirts use a rolled-on application process for a durable bond that 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 durability.
This NAMURA top-end kit is designed to fit 2012–2014 Honda TRX400X models and 1999–2005 Honda TRX400EX Sportrax models. Verify the cylinder bore, compression ratio, and application before installation to confirm compatibility. The manufacturer part number is NA-10003-4K, and the vendor part number is 186-10034.
Features:
- Complete top-end kit includes piston, rings, wrist pin, retaining clips, top-end bearing, and gasket kit
- Size: 85.97 mm +1.00 oversize piston diameter
- Compression Ratio: 11:1 high-compression design
- Brand: NAMURA
- Manufacturer Part Number: NA-10003-4K
- Vendor Part Number: 186-10034
- MOS2 Teflon/molybdenum-coated skirts help 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 reduced expansion, increased wear resistance, and improved high-temperature performance
- Fitment: 2012–2014 Honda TRX400X
- Fitment: 1999–2005 Honda TRX400EX Sportrax
Fitment:
1996 Honda XR400R
1997 Honda XR400R
1998 Honda XR400R
1999 Honda TRX400EX Sportrax
1999 Honda XR400R
2000 Honda TRX400EX Sportrax
2000 Honda XR400R
2001 Honda TRX400EX Sportrax
2001 Honda XR400R
2002 Honda TRX400EX Sportrax
2002 Honda XR400R
2003 Honda TRX400EX Sportrax
2003 Honda XR400R
2004 Honda TRX400EX Sportrax
2004 Honda XR400R
2005 Honda TRX400EX Sportrax
2006 Honda TRX400EX Sportrax
2007 Honda TRX400EX Sportrax
2008 Honda TRX400EX Sportrax
2009 Honda TRX400EX Sportrax
2012 Honda TRX400X
2013 Honda TRX400X
2014 Honda TRX400X