Yamaha - Gear 1 assy - 6H4-45560-01-00Yamaha Gear 1 Assembly Lower Unit Gearcase Component 6H4 45560 01 00 Overview When you open up a lower unit and find gear damage, its usually not subtleyoull hear it and feel it when running. Ive 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 its set up right, everything runs smoother, quieter, and more