Yamaha - Idle Gear Assembly Engine Timing Component YF1-52712-40-10. Overview. If you've ever had a Yamaha engine apart, you know the gear train is what keeps everything moving in sync. The Yamaha Idle Gear Assembly YF1-52712-40-10 plays a key role in transferring rotation between internal engine gears so timing stays exactly where it should. It's one of those components you don't see once the engine is closed up, but the whole system relies on it running smoothly. When the gear train is quiet a