The NAMURA NA-40010-4K Top End Kit is designed for Yamaha 660 ATV and side-by-side applications requiring a reliable piston and top-end rebuild solution. This kit features a 100.97 mm bore piston with an 11:1 compression ratio and is engineered to fit select Yamaha YFM660FG Grizzly 4WD [IRS] models from 2002 through 2008, along with Yamaha YXR660F Rhino 660 models from 2004 through 2006. The kit provides the key components needed to service the upper portion of the engine and restore dependable performance.
Each NAMURA top-end kit includes a piston, piston rings, wrist pin, retaining clips, top-end bearing, and gasket kit. The piston uses a hypereutectic casting process that increases silicon content for controlled expansion, improved wear resistance, and the ability to withstand elevated cylinder temperatures. A machined smooth head helps reflect combustion heat and reduce carbon buildup, while the anodized dome improves heat resistance and durability.
The piston skirts are treated with NAMURA MOS2, a Teflon and molybdenum coating applied through a rolled-on process. This coating is designed to create a strong bond while reducing friction, improving heat transfer, and helping minimize the risk of cold seizures. The result is a durable top-end replacement intended for off-road vehicles that demand consistent operation under demanding riding and working conditions. Confirm the vehicle year, model, engine configuration, and required bore size before installation.
Fitment: 2002–2008 Yamaha YFM660FG Grizzly 4WD [IRS]; 2004–2006 Yamaha YXR660F Rhino 660.
Features:
- Complete top-end kit includes piston, rings, wrist pin, retaining clips, top-end bearing, and gasket kit
- 100.97 mm bore piston with an 11:1 compression ratio for compatible Yamaha 660 engines
- MOS2 Teflon and molybdenum coated skirts help reduce friction, improve heat transfer, and minimize cold seizure risk
- Machined smooth piston head reflects combustion heat and helps reduce carbon buildup
- Anodized piston dome improves heat resistance and durability
- Hypereutectic casting process provides controlled expansion, increased wear resistance, and improved high-temperature performance
- Fits select 2002–2008 Yamaha YFM660FG Grizzly 4WD [IRS] models and 2004–2006 Yamaha YXR660F Rhino 660 models
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]