Yamaha - Gear 1 Assembly Lower Unit Gearcase Component 6H4-45560-01-00. Overview. When you open up a lower unit and find gear damage, it's usually not subtle-you'll hear it and feel it when running. I've worked on plenty of Yamahas where worn gears caused rough engagement or that unmistakable grinding sound. This assembly is a key part of getting the drivetrain back to where it should be. Once it's set up right, everything runs smoother, quieter, and more dependable out on the water.. Key Features. Complete Gear Assembly - Provides a ready-to-install solution for worn or damaged internal gear components.. Precision Gear Mesh - Designed for proper engagement and smooth operation within the gearcase.. Hardened Construction - Built to withstand load, torque, and continuous marine use.. OEM-Spec Dimensions - Matches Yamaha tolerances for correct alignment and performance.. Reliable Power Transfer - Supports consistent propulsion without slipping or abnormal noise.. Engine & Boat Compatibil