Yamaha - F70 Lower Unit Assembly Lower Unit 6CJ-45300-30-8D. Overview. On the F70, the lower unit is what keeps everything feeling smooth when you shift and get up on plane. It's not a huge motor, but it still relies on solid, consistent power transfer to perform right. I've worked on a few where a worn unit caused noise and rough engagement, and replacing it made the motor feel like new again. When it's dialed in, you get clean shifting and dependable performance every time you're out.. Key Features. • Smooth Power Transfer - Delivers consistent propulsion with clean gear engagement.• Compact High-Efficiency Design - Built to support mid-range horsepower engines without unnecessary strain.• Precision Gear Alignment - Helps reduce vibration and ensures proper internal operation.• Durable Marine Construction - Designed to resist corrosion and wear in tough environments.• Factory-Spec Fitment - Matches Yamaha standards for proper installation and reliable performance.. Engine & Boat Comp