The Namura NA-50004K Top End Kit is a complete standard-bore engine rebuild solution for select Polaris 500 ATVs. Designed for dependable fitment and performance, this kit includes a piston, piston rings, wrist pin, wrist-pin clips, top-end bearing, and gasket kit. It is engineered for a 91.97 mm bore and 11:1 compression ratio, making it suitable for restoring top-end performance on compatible Polaris engines.
Namura uses a hypereutectic casting process to provide increased silicon content, controlled expansion, and improved wear resistance under elevated cylinder temperatures. The piston features MOS2, or Teflon and molybdenum, coated skirts applied through a rolled-on process that creates a durable bond. This coating helps reduce friction, improve heat transfer, and minimize the risk of cold seizures during operation. The machined smooth piston head helps reflect combustion heat and resist carbon buildup, while the anodized dome improves heat resistance and durability.
This Namura top-end kit fits the 1998 and 1999 Polaris Big Boss 500 6X6; 1997 Polaris Xplorer 500 4X4; and 2000 through 2006 Polaris Scrambler 500 4X4. Verify the vehicle model, year, bore specification, and compression ratio before installation. The manufacturer part number is NA-50004K, and the vendor part number is 186-5004.
Features:
- Complete top-end kit with piston, rings, wrist pin, clips, top-end bearing, and gasket kit
- 91.97 mm standard-bore piston with an 11:1 compression ratio
- MOS2 Teflon and 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 dome increases heat resistance and piston durability
- Hypereutectic casting process provides controlled expansion, wear resistance, and improved high-temperature performance
- Fits 1998-1999 Polaris Big Boss 500 6X6, 1997 Polaris Xplorer 500 4X4, and 2000-2006 Polaris Scrambler 500 4X4
- Brand: Namura; Manufacturer part number: NA-50004K; Vendor part number: 186-5004
Fitment:
1996 Polaris Sportsman 500 4X4
1997 Polaris Scrambler 500 4X4
1997 Polaris Sportsman 500 4X4
1997 Polaris Xplorer 500 4X4
1998 Polaris Big Boss 500 6X6
1998 Polaris Scrambler 500 4X4
1998 Polaris Sportsman 500 4X4
1999 Polaris Big Boss 500 6X6
1999 Polaris Magnum 500 4X4
1999 Polaris Scrambler 500 4X4
1999 Polaris Sportsman 500 4X4
2000 Polaris Magnum 500 4X4
2000 Polaris Scrambler 500 4X4
2000 Polaris Sportsman 500 4X4
2001 Polaris Magnum 500 4X4
2001 Polaris Ranger 500 4X4
2001 Polaris Scrambler 500 2X4
2001 Polaris Scrambler 500 4X4
2002 Polaris Magnum 500 2X4
2002 Polaris Magnum 500 4X4
2002 Polaris Ranger 500 4X4
2002 Polaris Scrambler 500 2X4
2002 Polaris Scrambler 500 4X4
2003 Polaris Magnum 500 4X4
2003 Polaris Ranger 500 4X4
2003 Polaris Scrambler 500 4X4
2004 Polaris Atp 500
2004 Polaris Ranger 500 4X4
2004 Polaris Scrambler 500 4X4
2005 Polaris Atp 500
2005 Polaris Ranger 500 2X4
2005 Polaris Ranger 500 4X4
2005 Polaris Scrambler 500 4X4
2006 Polaris Ranger 500 2X4
2006 Polaris Ranger 500 4X4
2006 Polaris Scrambler 500 4X4
2007 Polaris Ranger 500 2X4
2007 Polaris Ranger 500 4X4
2007 Polaris Scrambler 500 4X4
2008 Polaris Ranger 500 2X4
2008 Polaris Scrambler 500 4X4
2009 Polaris Scrambler 500 4X4
2010 Polaris Scrambler 500 4X4
2011 Polaris Scrambler 500 4X4
2012 Polaris Scrambler 500 4X4