The NAMURA NA-40004-2 Piston Kit is designed for select Yamaha 660cc off-road applications and features a 100.47 mm piston diameter with a +0.50 mm oversize specification and a 9.2:1 compression ratio. This replacement piston kit supports engine rebuilding and restoration when the cylinder has been professionally bored and honed to match the piston size.
Fitment includes 2002–2008 Yamaha YFM660FG Grizzly 4WD [IRS] models and 2004–2006 Yamaha YXR660F Rhino 660 models. Verify the vehicle model, year, engine configuration, and required bore size before ordering to ensure proper application. The manufacturer part number is NA-40004-2, and the vendor part number is 187-400042.
Important: This NAMURA piston kit will not accept OEM piston rings, and the included or compatible replacement rings will not work with an OEM piston. Use the correct matching piston and ring set together, and follow the manufacturer’s clearance, installation, and break-in specifications. Professional installation is recommended for accurate cylinder preparation and reliable engine performance.
Features:
- Size: 100.47 mm piston diameter with +0.50 mm oversize specification
- Compression Ratio: 9.2:1
- Application: Replacement piston kit for select Yamaha 660cc ATV and utility vehicle engines
- Fitment: 2002–2008 Yamaha YFM660FG Grizzly 4WD [IRS]
- Fitment: 2004–2006 Yamaha YXR660F Rhino 660
- Brand: NAMURA
- Manufacturer Part Number: NA-40004-2
- Vendor Part Number: 187-400042
- Compatibility: Will not accept OEM rings, and the matching replacement rings will not work on an OEM piston
Fitment:
2001 Yamaha YFM660R Raptor
2002 Yamaha YFM660FG Grizzly 4WD [IRS]
2002 Yamaha YFM660R Raptor
2003 Yamaha YFM660FG Grizzly 4WD [IRS]
2003 Yamaha YFM660R Raptor
2004 Yamaha YFM660FG Grizzly 4WD [IRS]
2004 Yamaha YFM660R Raptor
2004 Yamaha YXR660F Rhino 660
2005 Yamaha YFM660FG Grizzly 4WD [IRS]
2005 Yamaha YFM660R Raptor
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]