Yamaha - Lower Unit Assembly Gearcase & Propulsion System 6EE-G5300-10-4D. Overview. When a small motor like an F4 or F6 starts losing smoothness or making noise down low, it's usually the lower unit telling you something's off. I've worked on plenty of these smaller Yamahas, and swapping in a complete assembly is often the cleanest fix. It saves time and gets everything back in line without chasing individual parts. Once it's on, the motor runs quiet and pushes like it should again.. Key Featur