The NAMURA NA-50026K Top End Kit is a standard-bore replacement kit designed for select Polaris ATV and utility vehicle applications. This 87.89 mm piston kit features an 11:1 compression ratio and includes the piston, piston rings, wrist pin, retaining clips, top-end bearing, and gasket kit for a complete upper-engine refresh. The kit is manufactured by NAMURA and is identified by manufacturer and vendor part number NA-50026K.
Engineered for durability and reliable performance, the piston uses a hypereutectic casting process that increases silicon content to help control expansion, improve wear resistance, and withstand elevated cylinder temperatures. The MOS2, or Teflon/molybdenum, coated skirt is applied using a rolled-on process that creates a strong bond while helping reduce friction, improve heat transfer, and minimize the risk of cold seizures. A machined smooth head helps reflect combustion heat and resist carbon buildup, while the anodized dome enhances heat resistance and piston durability.
This NAMURA top-end rebuild kit fits 2008–2012 Polaris Sportsman 400 HO 2x4 models, 2006–2007 Polaris Sportsman 450 models, and 2010–2012 Polaris Ranger 400 4X4 Midsize models. Verify the vehicle year, model, engine configuration, bore specification, and compression requirements before installation. The kit is intended for top-end service and provides the key components needed to restore dependable compression and engine operation.
Features:
- Fitment: Designed for select Polaris Sportsman 400 HO 2x4, Sportsman 450, and Ranger 400 4X4 Midsize models from 2006 through 2012
- Bore Size: 87.89 mm standard-bore piston specification
- Compression Ratio: 11:1 design for compatible engine applications
- Kit Contents: Includes piston, rings, wrist pin, retaining clips, top-end bearing, and gasket kit
- Skirt Coating: MOS2 Teflon/molybdenum coating helps reduce friction, improve heat transfer, and minimize cold-seizure risk
- Piston Construction: Hypereutectic casting provides controlled expansion and increased wear resistance
- Dome Treatment: Anodized dome improves heat resistance and durability
- Head Design: Machined smooth piston head helps reflect combustion heat and reduce carbon buildup
- Brand and Part Number: NAMURA NA-50026K
Fitment:
2001 Polaris Sportsman 400 4X4
2002 Polaris Sportsman 400 4X4
2003 Polaris Sportsman 400 4X4
2004 Polaris Sportsman 400 4X4
2005 Polaris Sportsman 400 4X4
2006 Polaris Sportsman 450
2007 Polaris Sportsman 450
2008 Polaris Sportsman 400 HO 2x4
2009 Polaris Sportsman 400 HO 2x4
2010 Polaris Ranger 400 4X4 [Midsize]
2010 Polaris Sportsman 400 HO 2x4
2011 Polaris Ranger 400 4X4 [Midsize]
2011 Polaris Sportsman 400 HO 2x4
2012 Polaris Hawkeye 400 HO 2x4
2012 Polaris Ranger 400 4X4 [Midsize]
2012 Polaris Sportsman 400 HO 2x4
2013 Polaris Hawkeye 400 HO 2x4
2013 Polaris Ranger 400 4X4 [Midsize]
2014 Polaris Hawkeye 400 HO 2x4
2014 Polaris Ranger 400 4X4 [Midsize]