This is more electrical than machine shop but somewhere in the collected wisdom of the group will be an answer. Normally an electric brush type motor will have "no"sparking at the armature, what does sparking indicate and what is the cure. This occurred on a built-in vacuum cleaner motor. Relay/switch module failed, bypassing the module allowed the motor to run normally. Pulled the brushes, lots of brush left and free movement - reinstalled brushes in same position lots of sparks. All advice appreciated.
I've done a fair amount of commutator turning and small motor repair. If the motor has had a lot of use, the commutator can be grooved and pitted or adjacent bars can even be shorted by accumulated brush dust and gunk. If you didn't get the brushes back into the same holes they came out of, you'll get a lot of sparking until they wear in again. I had one commutator that was like .030" eccentric, that one chewed up brushes like crazy until I turned it. On some DC/universal motors, you can move the brush holders until they're in the best position where sparking is least, not many small motors have that feature but it's handy. You'll always get a small amount of sparking, but it's not like the ring of sparks you'll get from bad brush position, poor brush fit or a shorted commutator bar. With the proper tooling, it only takes like 10 minutes to turn a small motor commutator and maybe that much again to undercut the commutator grooves with a hand tool. I usually use a ground-down hacksaw blade for that. On some vacuum cleaners, getting the armature out is the toughest part of the job, they really want you to toss the whole works and buy a new one.
If you can find a "Commutator brush seating stone", try using it against the spinning commutator while the motor is running. (Please don't electrocute yourself.)
I had one of them back when I encountered more "universal" brush type motors. It was a soft white abrasive stone about 4" long and maybe 3/8" x 3/16" cross section. I could usually find a path to shove it through so the end could reach the commutator, though YMMV.
You can probably still get them through automotive electrical supply places.
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