Racestar 140kv motors making knocking sound

Any idea what this is about? These are almost new with about than 25 miles on them. They don’t make this noise if I am riding and accelerating but when I let go of the trigger and just let the board coast this clacking comes back.

Try decreasing the belt tension (looser). Could be a motor bearing or loose magnet. Just ride it til it dies.

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If magnet is loose, one could probably secure it with epoxy and see if that knock goes away.

I don’t know how both the motors developed the same problem at the same time. This is really frustrating, opening these motors is basically next to impossible. Also my belt was so loose that it was basically skipping teeth every time I braked hard so can’t be that.

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I have the same issue with multiple motors, used and new. I’ve discontinued using them on any other new stuff I make. They seem to function just fine. It’s just annoying as all get-out.

How “true” is the shaft? Is there a noticeable wobble if you spin up the motor without a belt on?

If it’s not making a difference in performance, and it’s only audible, then just keep running them. Maybe order a couple more as backups.


Bearing issue clearly. Motor shouldn’t make any sound. If magnet comes loose, the motor wont work. It will ripped off and get jammed. If it’s just at the tip of breaking, when the magnet in contact with the stator, it will create spark.

Could the set screw on the pulley be loose?

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is there a short to ground from one of the phases ? Careful with the screw into the motor where the cables come out from.

HOLY SHIT! how did you know that? That was exactly what the problem was, i tightened the grub screw and the noise went away! Thanks so much, I was about to open the motors make it a shit show and waste sooooo much time.


I would try a dog tail set screw they are used to make sure everything is lined up properly