I have a Black & Decker KS850 Circular Saw which was spinning sporadically so I have taken it apart to investigate. I think there may have been a loose piece of plastic that had broken off from the motor mounting but it doesn't look that important so I chucked it out. The motor is sat firmly in position.

I tested it and notice that it was creating large sparks and getting hot without being stress tested, as in, it was just spinning without being used to cut through anything.

Can you please tell me what you think is causing this?

I have included a video example.


Parts: https://www.2helpu.com/PDMSDocuments/EU/Docs/Service%20Dossier/KS864_1D.PDF


1 Answer 1


Looks like it might need new carbon brushes, or maybe the motor commutator is worn out.

If the plastic piece that wasn't important to you was a part of what holds the brushes, rotor, armature, commutator, or any motor pieces in place then you could have mis-alignment of any of the above that might cause sparking like that. Take the motor housing apart and look closely for crooked stuff, there should be some blue/black marks from that sparking to clue you in.

P.S.- unplug the saw first

  • Hello Jimmy, thank you for your reply. I can confirm that everything is nicely lined up and there is no play in the motor seating. I did spin the armature by hand and noticed that there is one particular section at the rear of part number 368877-02 which makes the two brushes move outward when the bit in between them spins a revolution. It looks like it is sticking out slightly too much.
    – ShaunHill
    Apr 8, 2017 at 5:27
  • Will the metal bit grind down so that it is even like the rest or does it need replacing? The amount of movement is less than 1mm (although exactly how much I couldn't say). Having run it for a bit the sparks have reduced significantly.
    – ShaunHill
    Apr 8, 2017 at 5:37

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