Worm Drive circular saw sparking

[Acharya Kumarswami]

Our Bosch circular saw is having trouble.
It has been sparking for a while, apparently at the contact of the brushes (others were using it and did not attend to this problem).
Yesterday I encountered it, and it was worse, of course, to the point of almost not running at all.

I checked the brushes. The one on the left side (source of most sparking) was worn down to about 3/8" length.
The right brush was twice that long. I replaced both with new brushes, but the saw is still sparking. Can I hope that the sparking with diminish as the new brushes get broken in? Or is the saw a gonner?

[Ken Fitzgerald]

Try blowing the motor out with some low pressure air. Often a lot of brush dust will build up and cause problems.

[Bill Huber]

I would pull it down and clean the commutator, between each segment and if the brushes look a little worn I would replace them.

[mickey cassiba]

IMO not having seen the saw, you have an accumulation of carbon and or wood dust in the brush holder. New brushes are in order. before mounting them, clean the holder. Commutator cleaning is easily done with a pencil eraser, unless the gaps(black stripes) are glossed over. A toothpick is your friend here. LIGHTLY scrape the gaps with a toothpick. Do not file or sand...the varnish is there for a reason. With the new brushes installed in clean guides run the saw up and polish the comm with the pencil eraser. Sparks will diminish as you watch. Worst case is a broken or burnt guide that is actually rubbing against the comm. I haven't run into this on a Bosch, but I have on other brands. Still not a hard fix.

[Myk Rian]

I don't think the previous 3 commenters read your post.
You already replaced the brushes, so that's done.
The commutator needs to be turned and the mica insulation should be slotted just below the contacts.