Yamaha - Gear Lower Unit Gear 6D1-45571-00-00. Overview. When you're inside a Yamaha lower unit, you realize pretty quickly that every gear has to pull its weight. This gear is part of that system that keeps everything turning smoothly when you're shifting and running under load. I've worked on setups where a worn gear threw off the whole feel of the motor, from noise to performance. Replace it with a solid one like this, and you get back that smooth, dependable operation you expect out on the water.. Key Features. • Precision Gear Cut - Designed for smooth engagement and consistent rotation within the lower unit.• High-Strength Construction - Built to handle torque and stress from regular marine use.• Reliable Power Transfer - Supports efficient movement of power through the drivetrain.• Factory-Spec Fitment - Matches Yamaha tolerances for proper alignment and performance.• Wear-Resistant Surface - Helps protect against internal wear and corrosion in marine environments.. Engine & Boa