Yamaha YZ125 / YZ125X 58mm 144cc Athena Big Bore Kit – Top End Rebuild (2005–2022)

🛠️ Description
Turn your Yamaha YZ125 into a 144cc race weapon with the Athena Big Bore Kit. Designed for 2005–2021 YZ125 and 2020–2022 YZ125X, this kit adds serious horsepower and torque while maintaining OEM-level reliability. Includes all top-end components, from cylinder to piston and gaskets, with Athena’s proven engineering and materials.

✅ What’s Included

• Athena 58mm Nikasil Big Bore Cylinder (144cc)

• Athena Coated Piston Kit (Piston, Rings, Wrist Pin, Circlips)

• Athena Complete Top End Gasket Set

• Athena Cylinder Head w/ Removable Bronze Dome

• Athena Head Stud Kit

• Athena High-Performance Anodized Power Valves (OEM valves not compatible)

• All components brand new, covered by Athena’s warranty

📦 Fitment

• Yamaha YZ125 (2005–2021)

• Yamaha YZ125X (2020–2022)

🛡️ Warranty Info

• Manufacturer warranty included

• Professional installation required — improper tuning, break-in, or setup voids warranty

• Case boring may be required for installation

🔑 Key Features

• Boosts displacement from 125cc → 144cc for major power gains

• Aluminum cylinder with nickel-carbide coating for maximum durability

• Includes complete Athena top-end kit with piston, gaskets, head, and valves

• Race-ready with improved torque and top-end pull

• Direct OEM fitment — designed specifically for YZ125 and YZ125X