The NAMURA NA-40010K Top End Kit is designed for Yamaha 660 ATV and utility vehicle applications requiring a reliable standard-bore piston assembly. This complete kit includes a piston, piston rings, wrist pin, retaining clips, top-end bearing, and gasket kit for a comprehensive top-end refresh. With a 99.97 mm standard-bore piston and 11:1 compression ratio, it is engineered to support dependable engine performance and proper fitment in compatible cylinders.
The piston uses NAMURA’s MOS2, or Teflon/Molybdenum, coated skirts. The rolled-on coating process creates a durable bond while helping reduce friction, improve heat transfer, and minimize the risk of cold seizures. Machined smooth heads help reflect combustion heat and reduce carbon buildup, supporting piston protection during operation. Anodized domes add heat resistance and durability, while the hypereutectic casting process provides increased silicon content for controlled expansion, improved wear resistance, and greater tolerance of elevated cylinder temperatures.
This NAMURA top-end kit fits 2002–2008 Yamaha YFM660FG Grizzly 4WD models with independent rear suspension and 2004–2006 Yamaha YXR660F Rhino 660 models. Confirm the exact year, model designation, bore specification, and compression requirements before installation. The manufacturer part number is NA-40010K, and the vendor part number is 186-4010.
Features:
- Complete top-end kit includes piston, rings, wrist pin, retaining clips, top-end bearing, and gasket kit
- 99.97 mm standard-bore piston with an 11:1 compression ratio
- 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 dome improves heat resistance and piston durability
- Hypereutectic casting process provides controlled expansion, improved wear resistance, and increased tolerance of high cylinder temperatures
- Brand: NAMURA
- Manufacturer part number: NA-40010K
- Vendor part number: 186-4010
- Fitment: 2002–2008 Yamaha YFM660FG Grizzly 4WD with independent rear suspension and 2004–2006 Yamaha YXR660F Rhino 660
Fitment:
2002 Yamaha YFM660FG Grizzly 4WD [IRS]
2003 Yamaha YFM660FG Grizzly 4WD [IRS]
2004 Yamaha YFM660FG Grizzly 4WD [IRS]
2004 Yamaha YXR660F Rhino 660
2005 Yamaha YFM660FG Grizzly 4WD [IRS]
2005 Yamaha YXR660F Rhino 660
2006 Yamaha YFM660FG Grizzly 4WD [IRS]
2006 Yamaha YXR660F Rhino 660
2007 Yamaha YFM660FG Grizzly 4WD [IRS]
2007 Yamaha YXR660F Rhino 660
2008 Yamaha YFM660FG Grizzly 4WD [IRS]