Yamaha - LZ300 Lower Unit Assembly Lower Unit 6D1-45300-20-8D. Overview. Working on LZ300 setups, you learn quick that the lower unit has to be solid from the start. These motors push hard, and if the gearcase isn't right, you'll feel it in the way it shifts and runs. I've swapped out worn units before, and the difference is immediate-quieter, smoother, and more predictable on throttle. This is the kind of part you put in when you want to trust your setup every time you head out.. Key Features. • High Horsepower Ready Design - Built to handle the demands of large Yamaha outboards under load.• Smooth Gear Engagement - Supports clean shifting and consistent performance through the drivetrain.• Precision Internal Alignment - Ensures proper gear mesh to reduce vibration and wear.• Durable Marine Construction - Holds up against harsh freshwater and saltwater conditions.• Direct Fit Replacement - Designed to match Yamaha specifications for proper installation and operation.. Engine & Boat Co