The NAMURA NA-40010-6K Top End Kit is designed for select Yamaha 660cc ATV and side-by-side applications. This 101.47 mm, approximately 4-inch, oversized kit features an 11:1 compression ratio and includes the essential components needed to refresh the upper end of the engine. The kit contains a piston, piston rings, wrist pin, retaining clips, top-end bearing, and gasket kit for a comprehensive installation.
Engineered for dependable performance, the piston uses a hypereutectic casting process with increased silicon content. This construction helps reduce expansion, improve wear resistance, and withstand elevated cylinder temperatures. The piston skirt features NAMURA’s MOS2, or Teflon/molybdenum, coating. Its rolled-on application creates a strong bond that helps reduce friction, improve heat transfer, and minimize the risk of cold seizures.
The machined smooth piston head helps reflect combustion heat and reduce carbon buildup, supporting durability and consistent operation. An anodized dome improves heat resistance and strength compared with non-anodized designs. Together, these features help protect the piston under demanding riding conditions while supporting reliable engine performance.
The NAMURA NA-40010-6K fits 2002–2008 Yamaha YFM660FG Grizzly 4WD IRS models and 2004–2006 Yamaha YXR660F Rhino 660 models. Verify the vehicle year, model, bore requirement, and compression specifications before installation. This is a top-end replacement kit intended for compatible Yamaha 660 engines.
Features:
- Complete Top End Kit: Includes piston, rings, wrist pin, retaining clips, top-end bearing, and gasket kit.
- 101.47 mm Bore: Provides an approximately 4-inch piston diameter with a 1.50 mm oversize specification.
- 11:1 Compression Ratio: Designed for compatible Yamaha 660 engine applications.
- MOS2-Coated Skirt: Rolled-on Teflon and molybdenum coating helps reduce friction, improve heat transfer, and minimize cold-seizure risk.
- Machined Smooth Head: Helps reflect combustion heat and reduce carbon buildup on the piston crown.
- Anodized Dome: Improves heat resistance and durability for demanding operating conditions.
- Hypereutectic Construction: Increased silicon content helps reduce expansion, improve wear resistance, and withstand higher cylinder temperatures.
- Fitment: Compatible with 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]