Heavy Duty Alternator

Tech Tip: Starting Motor Gear Differences

Have you ever gone to replace a starting motor and discovered that the recommended replacement starter has a different pinion than the original unit? Good news, it can still be used for the replacement.
Starting motor pinions and drive assemblies are specifically designed to match the engine ring gear for proper mesh and performance.

If you’re dealing with an older application:
  • Conduct a quick check of the engine type to make sure it has not been replaced.
  • Next, confirm that your recommended replacement model is appropriate for the engine being serviced.
  • Check the removed starter pinion and engine ring gear for damage. Putting a good starter on a damaged ring gear will most likely damage the starter pinion.
  • Verify the ring gear tooth count for the engine being serviced. After verifying the engine, ring gear and starter, you can still use a starter with a different pinion.
This is acceptable because most starting motors have a pinion centered in the drive end mounting that mates with the ring gear when energized (Figure A). Starting motors can be optimized with a pinion change to match the engine characteristics. Because the engine ring gear is fixed, any change to the pinion would require an offset to the shaft position in order to properly mesh with the ring gear (Figure B).
Performance between the two designs should be fairly compatible and suitable for replacement. The pinion differences exist to better match the motor performance with engine needs for a given motor family or manufacturer.
If you have any questions, visit delcoremy.com, or contact us at 800-372-0222.

Watch our short Tech Tip video to learn more about what to do when a replacement starter has a different pinion than the original unit. 

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