2000-2008 Yamaha YFM Big Bear 400 ATV Engine Piston Kit [Bore Size (mm): 84.5] Bore Size (mm): 84.5 Piston Kits Include Piston, Piston Rings, Pin and Circlip High Silicone Content for Additional Strength All Namura Pistons have Molybdenium/Teflon Skirt Coatings that Minimize Resistance and Wear to Provide Extended Life Compatibility: 2000-2008 Yamaha YFM Big Bear 400