Yamaha - Lower Unit Assembly Complete Drivetrain 6K5-45300-14-4D. Overview. The Yamaha Lower Unit Assembly 6K5-45300-14-4D is the heart of how your outboard puts power into the water. When a lower unit starts going-gears, seals, or bearings-you'll feel it in vibration, noise, or loss of performance. Swapping in a complete unit like this saves time and takes the guesswork out of piecing things back together. It's a solid move when you want everything running smooth again without chasing internal issues.. Key Features. • Complete Drivetrain Assembly - Includes essential internal components for full lower unit operation.. • Smooth Power Transfer - Delivers engine output efficiently to the propeller.. • Corrosion-Resistant Build - Designed to hold up in harsh saltwater and freshwater conditions.. • OEM Fit and Alignment - Matches Yamaha specifications for proper installation and performance.. • Superseded Design Update - Replaced by newer version for continued support and compatibility.. E