Yamaha - Lower Unit Assembly Gearcase Component 6M8-G5300-11-4D. Overview. The lower unit is where all that engine power finally turns into movement, so when it's off, you feel it immediately. I've seen setups lose smoothness, get noisy, or just not push right because the gearcase was worn out. Bolt on a solid assembly like this, and everything tightens back up-clean shifting, steady power, and a smoother ride. It's one of those upgrades that brings confidence back every time you head out.. Key Features. • Complete Gearcase Assembly - Provides a full replacement with properly matched internal components.• Efficient Power Transfer - Delivers smooth and consistent output to the propeller.• OEM Precision Fit - Built to Yamaha specifications for accurate alignment and installation.• Corrosion-Resistant Construction - Designed to withstand harsh marine environments.. Engine & Boat Compatibility. Designed for Yamaha outboard engines requiring dependable gearcase performance. Commonly used ac