Yamaha - LZ300 Lower Unit Assembly Lower Unit 6D1-45300-30-8D. Overview. On LZ300 setups, the lower unit is doing serious work every time you throttle up. If it's not right, you'll feel it in the way the boat responds-especially under load. I've swapped out worn units that caused noise and rough shifting, and the difference with a solid replacement is night and day. When everything lines up right, you get smooth power delivery and a setup you can trust out on the water.. Key Features. • High Load Gearcase Design - Built to handle the demands of high horsepower Yamaha outboards.• Consistent Power Transfer - Delivers smooth propulsion with reliable gear engagement.• Precision Internal Alignment - Helps reduce vibration and ensures proper gear mesh.• Marine-Grade Durability - Designed to resist corrosion and wear in harsh environments.• Factory-Spec Fitment - Matches Yamaha standards for proper installation and dependable performance.. Engine & Boat Compatibility. Designed for Yamaha LZ30