Yamaha - Idle Gear Assembly Engine Timing Component YF1-58752-40-13. Overview. If you've spent any time inside a Yamaha engine, you know the gear train is what keeps everything working in sync. The Yamaha Idle Gear Assembly YF1-58752-40-13 helps transfer rotational movement between internal gears so timing stays exactly where it should. It's not a flashy part, but it's critical for smooth engine operation. When the gear train is aligned and turning properly, the engine runs quieter, smoother, an