Yamaha - Lower Unit Assembly Gearcase Component 6P2-45300-20-8D. Overview. On these F250 motors, the lower unit is what you feel every time you shift and throttle up. I've seen boats lose efficiency and smoothness just from wear down there, even when the powerhead was still strong. Swapping in a complete assembly like this brings everything back to tight, quiet operation. It's the kind of fix that makes the boat feel solid again the moment you put it in gear.. Key Features. • Complete Gearcase Assembly - Provides a full replacement with properly matched internal components.• Smooth Power Transfer - Delivers consistent output from engine to propeller.• OEM Precision Fit - Built to Yamaha specifications for proper alignment and installation.• Corrosion-Resistant Construction - Designed to handle harsh marine environments.. Engine & Boat Compatibility. Designed for Yamaha F series outboard engines, including high-horsepower four stroke models. Commonly used across a range of Yamaha outboa