Yamaha - Lower Unit Assembly 60/70 HP Complete Drivetrain Assembly 6H3-45300-20-8D. Overview. The Yamaha Lower Unit Assembly 60/70 HP 6H3-45300-20-8D is what takes all that engine power and actually puts it to work in the water. When a lower unit starts going bad, you'll feel it right away-noise, vibration, or loss of push at the prop. Instead of tearing into gears and chasing problems, swapping the full assembly is usually the cleanest fix. It gives you a solid, dependable setup so you can get back on the water without second-guessing it.. 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 efficient thrust and consistent performance under load.. • Corrosion-Resistant Construction - Designed to handle harsh marine environments and long-term use.. Engine & Boat Compatibility