Your tool's motor uses two carbon brushes to conduct electricity to the armature. The brushes contact the armature's commutator. The carbon brush will wear down over time from rubbing against the rotating commutator (and will need to be replaced). Worn brushes can cause excessive sparks around the commutator. The sparks can also be caused by a damaged armature, so you'll want to carefully inspect both if sparks are present.
Let's get started.
REMOVING THE MOTOR BRUSHES 1. Remove the motor brushes.
a. Use a large screwdriver to remove the brush cap.
b. Remove the motor brush from the brush holder
c. Repeat this step to remove the second motor brush (on the opposite side of the motor).
INSTALLING THE NEW MOTOR BRUSHES
2. Install the motor brush.
a. Install the new motor brush into the brush holder.
b. Align the tabs on the end of the brush spring with the brush holder and compress the brush spring into the brush holder.
c. Secure the new motor brush with the brush cap (do not overtighten).
d. Repeat this step to install the second motor brush (on the opposite side of the motor).