Hi-TTS Flywheel Ring Gear 110 Teeth for Mitsubishi HD250 HD450 Excavator 4D31/4D31T Models ME012548 ME012549 Guangdong Made Describe: What is a flywheel ring gear? Starter ring gears are attached to either the flywheel or the flexplate of an engine. The teeth of the ring gear are driven by the smaller gear (known as the pinion) of the starter motor. The pinion engages the starter ring only during starting and once the engine is running the pinion withdraws. How do you know if