This product has been superseded by: 6D9-45300-34-8D. Yamaha - Lower Unit Assembly Gearcase Component 6D9-45300-33-8D. Overview. The Yamaha Lower Unit Assembly 6D9-45300-33-8D is built to keep your outboard running strong with smooth and reliable power transfer. This is the part that takes engine output and turns it into forward motion, so when it starts to fail, you'll notice it immediately-vibration, noise, or reduced performance. Designed to Yamaha's exact standards, this assembly restores proper function and keeps your motor operating the way it should on the water.. Key Features. • Efficient Power Transfer - Delivers smooth propulsion from engine to propeller.. • OEM Fit Precision - Engineered to Yamaha specifications for seamless installation and alignment.. • Complete Gearcase Assembly - Pre-assembled for reliable performance and easier replacement.. • Corrosion-Resistant Construction - Built to withstand harsh marine environments.. Engine & Boat Compatibility. • F90• F100. FAQs