I just finished taking apart the motor from my Duo-Art for general
cleaning.  First off, it should not make any noise when running.
You might be able to find something that shouldn't be there by looking
through the vent holes, and remove same without taking the motor apart.
If you are mechanically inclined, there is little need to take it to a
small motor repair shop.  I had no choice, as there is no such shop in
this town.

Breakdown is easy.  First off, mark the housing in some fashion so
that the front bell and body go back in the same place.  Remove the
pulley and then the screws around the perimeter which hold the housing
together.  You should only need to remove the front bell.  A gentle
tap with a soft mallet should release it.

Before pulling it off, make sure that the shaft is clean and free of
any burrs or dirt.  Clean as necessary as you don't want to damage the
front bearing.  The front bell should slip off the front shaft with
ease without the use of hammers, pliers, of pullers.

You will find that the front bell has two electrical wires connected,
but they fold out enough the allow access to the armature.  Leave them
alone for now and lay the front portion over.  Grab the shaft and pull
out the armature.  It will come right out.  Don't loose any of the
spacers or washers on either end.  If a piece of debris falls out
during this process, it may be the cause of the noise.

Clean the armature and shafts well.  There should be no wires or
insulation sticking out of the windings.  If there are, find a small
motor repair shop.

On the front the armature there are three pawls, which I think are
brushes.  Not certain of their function, but would guess it has
something to do with starting the motor (phase shift).  In any case,
these are spring-loaded and should return inward with ease after
pushing outward.  If they are not moving, they may be the cause of the
noise since they will be riding on the front contacts instead of being
swung out by centrifugal force.  Adjust as needed so they move freely.

That's about it for looking for noise.  Now back to those two wires.
They are old, wrapped in old cloth insulation, and probably cracked
when you folded them out.  Unsolder them from the two front contacts
-- those large brass semicircular things on the front bell.  I slipped
some heat shrink tubing over them, about 3/16".  No need to shrink.
It will act as a good insulator and will keep any bare wire from
touching the housing.  Solder back to their respective contact.

Apply some lubricant to the shafts, make sure the washers/spacers are
still in place, and reverse the process to reassemble.  That's it.

Lubrication:  I use a product available at Lowes Hardware in the tool
section.  It comes in a small can like 3-in-1 Oil and but is marked
specifically for small motors.  I forget the name, but it is not the
standard 3-in-1 Oil.  Fill each of the wells with the oil.  Let set
for a day or two.  Check back and add more if it's all gone.  Do this
several times, running the motor for a few moments between additions.
Call me if I can be of any more help.

Those small set screws:  I don't know their function either.  I could
not get mine to turn so I left them alone (If it ain't broke; don't fix
it).  I suspect they hold the bronze bushings in place, i.e., to keep
them from rotating.

Jim Quashnock