Yamaha - Lower Unit Assembly Complete Drivetrain Assembly 6HB-45300-02-8D. Overview. The Yamaha Lower Unit Assembly 6HB-45300-02-8D is what takes all that horsepower and actually turns it into push in the water. When something inside the lower unit starts going bad, you'll feel it quick-vibration, noise, or a drop in performance when you get on it. Instead of tearing into gears and hoping for the best, swapping the full assembly is usually the cleanest and most dependable fix. It gives you a solid setup again so you can run with confidence.. Key Features. • Complete Drivetrain Assembly - Replaces internal gears and components in one unit for reliable operation.. • OEM Fit Precision - Built to Yamaha specifications for proper alignment and straightforward installation.. • Smooth Power Transfer - Supports consistent thrust and dependable performance under load.. • Heavy-Duty Construction - Designed to handle high horsepower, torque, and harsh marine conditions.. Engine & Boat Compatibili