Yamaha - Lower Unit Assembly 8 HP Complete Drivetrain Assembly 6M8-G5300-00-4D. Overview. The Yamaha Lower Unit Assembly 8 HP 6M8-G5300-00-4D is what turns your engine's output into real movement in the water. When a lower unit starts wearing out, you'll notice it fast-vibration, noise, or reduced push when you throttle up. Instead of chasing worn gears or internal issues, swapping the full assembly is usually the most reliable fix. It gives you a fresh, solid setup so you can run without worrying about what's happening below the surface.. Key Features. • Complete Drivetrain Assembly - Replaces internal gears and components in one unit for dependable performance.. • OEM Fit Precision - Built to Yamaha specifications for proper alignment and straightforward installation.. • Smooth Power Transfer - Supports consistent thrust and reliable operation across all speeds.. • Corrosion-Resistant Construction - Designed to handle harsh marine environments and long-term use.. Engine & Boat Compat