My husbands Yard force lawn mower self propelled not starting after hitting something with blade. Does anyone have any suggestions?

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    Any competently designed lawnmower will have a "shear pin" which is a soft pin designed to fail first, preventing damage to more expensive parts. That is a good thing. Incompetent maintainers will often get angry and say "why did they use such a weak shear pin? Darn penny pinchers, I shall substitute a much stronger one." And then something expensive becomes the weak point. May 11, 2022 at 23:27
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    I’m voting to close this question because small motor repair belongs on Motor Vehicle Maintenance & Repair, not Home Improvement.
    – FreeMan
    May 12, 2022 at 15:09

1 Answer 1


There could be more than 1 issue but the most likely is the flywheel to crankshaft key has sheared. This is a square or offset cast piece that sets the timing of the magneto with the needed spark.

To protect the motor this key way shears.

Some mowers are very sensitive to the blades being in time and if a solid bracket on the blade and it has jumped this gave me a headache until I found it.

Most of the time I find it to be the key.

  • Hopefully the key sheers and not the keyway.
    – crip659
    May 11, 2022 at 21:15

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