Excavator 4BG1 4BD1 Flywheel Ring Gear 8-97175902-0 8971759020 128T Ring Flywheel Gear 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. Quick Details: Part No Flywheel Ring Gear Engine No.