Yamaha - Lower Unit Assembly Outboard Drivetrain 6M8-G5300-10-EK. Overview. When a lower unit starts going, you feel it right away-rough shifting, noise, and a loss of confidence on the water. This Yamaha assembly is the kind of replacement you put on and forget about because it just works the way it should. Everything lines up properly, and the motor feels smooth again under load. It's a solid choice whether you're maintaining a reliable setup or bringing an older outboard back to life.. Key Fe