Yamaha - Gear 1 Assembly Lower Unit Gear System 6L5-45560-00-00. Overview. When a lower unit starts making noise or slipping under load, it usually comes down to worn internal gears. This is one of those parts that takes constant stress every time you throttle up or shift. I've seen engines feel completely different just by replacing a worn gear assembly like this. Once it's in, everything runs smoother, quieter, and a lot more dependable.. Key Features. Precision-Cut Gear Teeth - Ensures smooth engagement and efficient power transfer.. High-Strength Construction - Built to handle torque and load without premature wear.. Factory-Spec Fitment - Designed to match Yamaha lower unit tolerances for proper operation.. Restores Drivetrain Performance - Helps eliminate slipping, noise, and rough operation.. Wear-Resistant Finish - Engineered to withstand continuous contact and high-speed rotation.. Engine & Boat Compatibility. Designed for Yamaha outboard engines with compatible lower unit gea