Yamaha Lower Unit Assembly 6CE-45300-15-8D. Overview. The Yamaha 6CE-45300-15-8D Lower Unit Assembly is a genuine original equipment manufacturer component designed to transfer engine power efficiently to the propeller. The lower unit houses critical drivetrain components, including gears, shafts, and bearings, that work together to convert engine output into smooth propeller rotation for reliable boat propulsion.. A properly functioning lower unit is essential for maintaining performance, maneu