In my lawmower's motor plastic fan/ventilator on rotor has broken to few pieces 1 2

There are 2 small springs in fan's slots.

What is the purpose of these springs?

Are there any standards for such components?

Edit: This is how it looks like in working motor: enter image description here

And in my disassembling lawnmower some years ago: enter image description here

Edit 2: Today I've got some other broken motor (burnt winding) but with fully operational fan so I was able to check it how it's working.

The simplest solutions are the best - this springs work as brake when motor is no longer supplied

Here are some photos how fan is mounted on the shaft and where are springs (bottom view): side view - cross section

bottom view

Springs are mounted inside fan and tightly touch fragment of the plastic on the top of stator. When motor starts spinning, centrifugal force "pushes" springs outside of stator so there is no sliding. When motor losts supply, rotor spins slower and springs start sliding of the plastic which stops rotor much faster than without it. Thanks to that we don't need to wait eternity to open basket and throw grass.

Due to friction between metal and plastic, it heats up and melts plastic on stator. I saw many small melted pieces around place where springs slide, so maybe my fan was destroyed by some bigger fragments of such melted pieces... I think manufacturer should put of the stator some rubber or some additional material between plastic and springs.

Anyway the topic can be closed. If you would have some more comments, feel free to write :)


I've checked how it looks like, and it turns out that springs are for break purpose to stop motor faster after releasing power button. During normal work centrifugal force pushes springs out of plastic on not rotating part (pic 5). After releasing power button centrifugal force is lowering which allows spring to touch and slide over plastic and slow motor in shorten time. I was able to test stopping motor without this springs and surprisingly motor stops only about 10-20% longer. Probably on "fresh" component when plastic is not melted yet it works better ;)

Anyway topic to close.

  • $\begingroup$ Out of the fan after it's broken. Normally there are inside small slot visible in the picture. Also you can check how it looks like in working motor: kosiarkijura.pl/images/Czesci_do_kosiarek/… $\endgroup$
    – voldi
    Sep 4, 2022 at 18:14
  • 1
    $\begingroup$ that picture belongs in your question above ... it certainly does not belong in a comment $\endgroup$
    – jsotola
    Sep 4, 2022 at 18:20
  • $\begingroup$ there is probably another component that is missing $\endgroup$
    – jsotola
    Sep 4, 2022 at 18:22
  • $\begingroup$ I've just showed you with the link in the comment above how it should look like in normal condition. I cannot upload my pictures in the comment so I will edit original post. $\endgroup$
    – voldi
    Sep 5, 2022 at 6:11
  • $\begingroup$ @voldi comments are not for pictures or further information so adding to the question is the correct behavior. Also, why not just buy the fan from the manufacturer? $\endgroup$
    – Solar Mike
    Sep 5, 2022 at 6:26

1 Answer 1


Seems that these springs abut to some part that sits on the motor shaft firmly, closer to motor. Then their purpose is to press fan wheel to the pulley which drives the belt while fan wheel fits on the shaft loosely. This works as friction clutch to prevent what had happened.

I experienced such hi-speed fan explosion in cheap wood router, and it was necessary to use particularly that tool. At first time we glued its parts and tightened it with aluminium hoops. After repeated breakage (that time it was "human factor") we made new wheel from aluminium on CNC milling machine, with much simpler geometry of course.

At first sight, it is possible to use one spring and put it on the motor shaft. This will allow to make simple fan wheel. It is hard to see, but seems it is made from polyacetal, it is hard to glue.


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