Yamaha - Lower Unit Assembly Gearcase Component 6N0-45300-00-4D. Overview. On smaller 6 and 8 horsepower motors, you really notice when the lower unit isn't right. I've worked on setups where the engine ran fine, but the drive felt rough or inefficient because the gearcase was worn out. Swap in a solid assembly like this, and everything smooths out-quiet operation, clean engagement, and better control. It's the kind of part that keeps a small motor running like it should.. Key Features. • Complete Gearcase Assembly - Provides a full replacement with properly matched internal components.• Smooth Power Transfer - Delivers consistent output for reliable propulsion.• OEM Precision Fit - Built to Yamaha specifications for correct alignment and installation.• Corrosion-Resistant Build - Designed to withstand harsh marine conditions.. Engine & Boat Compatibility. Designed for Yamaha 6 horsepower and 8 horsepower outboard engines. Commonly used across smaller Yamaha outboards where dependable