Yamaha - LZ300 Lower Unit Assembly Lower Unit 6D1-45300-40-8D. Overview. On the LZ300 setups, the lower unit takes a beating if you're running hard or spending long days offshore. This is one of those components you don't think about until something feels off-then you realize how much it affects everything from shifting to overall control. I've seen a fresh lower unit completely change how a motor runs, especially under load. When it's right, the boat feels smoother, quieter, and more responsive where it counts.. Key Features. • High Horsepower Gearcase Design - Built to handle the demands of large outboards under continuous load.• Smooth Power Transfer - Delivers consistent propulsion with clean gear engagement.• Precision Internal Setup - Ensures proper gear alignment for reduced vibration and wear.• Marine-Grade Durability - Holds up against corrosion and harsh on-water conditions.• Direct Yamaha Fitment - Engineered to match factory specifications for proper installation and operat