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How hard are starter pinions?

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  • How hard are starter pinions?

    I'm motorizing my bead roller, using a GM flexplate and starter pinion for 18.66:1 reduction between a 100 rpm gear motor and the driven shaft. To connect the motor shaft to the pinion I need to modify the pinion, which is HARD. Does anyone know whether such pinions are hard all the way through or just case hardened? Thx.

  • #2
    I doubt they are hardened all the way through. Probably a case hardening of sorts. I say this as the whole starter drive assembly is not all that overly expensive. You see the ring gear they engage with receiving the most damage from the drive & then requiring replacement. The damage is likely the result of the engine stopping most frequently in the same spot. Strange but true.


    • #3
      Probably not case hardened. Could be, for such a small gear, through hardened, but in any event, likely hardened 1.5 x the tooth depth or so, and maybe on the bore as well.
      CNC machines only go through the motions


      • #4
        I heated to orange (no magnet test), covered with sand and allowed to cool. Now I can cut it with carbide, but it's still plenty tough, and it work hardens. My guess is that it was case hardened or just work hardened by the forming process.


        • #5
          I would have just press fit it on to a shaft and designed it to work from there.



          • #6
            Doozer, That might have worked if requirements were slightly different. In this case, there were low-helix splines on the shaft that would have made a poor mating surface. I wanted to get the splines off. Could have brazed on a sleeve instead. Lots of ways to skin a cat.