Yamaha - Gear 2 Lower Unit Gearcase Component 6H4-45571-01-00. Overview. When you're dealing with gearcase issues, it's usually not something minor, and gears like this are right at the center of it. I've torn down lower units where worn or chipped gears were the reason for noise, slipping, or failure to stay in gear. It's not a quick fix job, but replacing the right components makes all the difference. When everything is set up correctly again, the motor runs smooth and quiet like it should.. Key Features. Precision Gear Engagement - Transfers power within the lower unit for smooth and reliable operation.. Hardened Gear Construction - Built to handle load and resist wear under continuous use.. OEM-Spec Machining - Designed to Yamaha tolerances for proper mesh and alignment.. Consistent Power Delivery - Supports steady propulsion without slipping or grinding.. Critical Drivetrain Component - Essential for proper gearcase function and long-term durability.. Engine & Boat Compatibility.