Starting Rings
The starter ring gear is a toothed steel ring fitted around the outer edge of the flywheel. The starter motor pinion engages these teeth to crank the engine when starting. It is usually fixed to the flywheel by an interference, or heat-shrink, fit.
When the driver starts the engine, the starter motor extends its small pinion gear to mesh with the ring gear teeth and spins the flywheel, turning the engine over until it fires. Once the engine starts, the pinion withdraws. The ring gear transfers the starter torque to the flywheel and engine.
Repeated starter engagement gradually wears the ring gear teeth, and misalignment of a replaced starter can wear them faster or damage them. Worn or broken teeth show up as a grinding noise during starting or as the engine failing to crank. Because the ring gear is fixed to the flywheel, a worn ring gear is replaced, and the starter alignment is checked to prevent a repeat.
The correct ring gear depends on the flywheel diameter and tooth count and the starter it works with. Confirm the part against the vehicle specification before fitting.
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Frequently asked questions
What does the starter ring gear do?
Its teeth mesh with the starter motor pinion so the starter can crank the engine when starting. It is fitted around the edge of the flywheel.
What are the signs of a worn ring gear?
A grinding noise when starting, or the engine not cranking, often from worn or broken teeth where the starter repeatedly engages.
Why do ring gear teeth wear out?
Repeated starter engagement wears them over time, and a misaligned starter can wear or chip them faster. Checking starter alignment helps prevent a repeat.
Can a ring gear be repaired?
Worn teeth generally mean the ring gear is replaced. A technician should also confirm the starter is aligned correctly so the new ring gear lasts.