Yamaha - Lower Unit Assembly Complete Drivetrain 6J8-45300-E2-4D. Overview. The Yamaha Lower Unit Assembly 6J8-45300-E2-4D 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 notice it quick-noise, vibration, or just not getting the push you expect. I've seen plenty of guys chase individual issues inside, but sometimes it's smarter to swap the whole unit and be done with it. This is the kind of replacement that gets you back to smooth, reliable running without second-guessing what's going on inside.. Key Features. • Complete Gearcase Assembly - Includes internal drivetrain components for full lower unit function.. • Smooth Power Delivery - Transfers engine output efficiently to the propeller.. • Corrosion-Resistant Construction - Built to handle harsh saltwater and freshwater environments.. • OEM Fit Alignment - Designed to match Yamaha specifications for proper installation.. Compatibility. Compatible with select Ya