While thousands of different sewing machine models and brands are available, most domestic sewing machines contain AC motors. Over time, carbon deposits collect inside AC motors, causing them to overheat, shut off or drag. One simple solution is to run the motor at top speed for a few minutes until the carbon burns and melts away. When that doesn't work, don't despair. With a few simple supplies, you can repair the electric motor in your sewing machine yourself.
Unplug your sewing machine. Using a screwdriver, remove the top, bottom and handwheel covers. Loosen the screws or bolts holding the motor in place. Loosen the screws attached to the motor pulley and separate the pulley from the rest of the machine. Put the screws safely aside for reassembly.
Remove the plastic strain relief from the electrical wire. If the wire is secured by a metal grommet, leave the grommet in place. Remove the bolts on the casting so it separates into two parts.
Unscrew the carbon caps, then remove the spring and carbon brushes beneath them. Remove the other casting piece by removing the two nuts that hold the long metal coil in place. Gently pull off the coil, release the rotor, and take out the centre armature. Slide off the little washers along the nose of the armature and tape them to a piece of paper in the same order you removed them.
Clean the copper contacts of the armature commutator by installing the armature on a hand drill. Turn on the drill and apply 400-grit sandpaper to the commutator as it spins. Apply 1500-grit sandpaper next, until the copper has a polished sheen. Do not touch the armature when you're done, or you'll put oily fingerprints on the newly cleaned surface.
Before reassembling the motor, soak the bolts and screws in soapy water. Clean the carbon brushes with alcohol. Reassembly begins with the armature. Hang all the washers along the nose in the same order you removed them. Slide the armature inside the casting. Put the field coil with its attached brush plate in place. Face the electrical wiring toward open casting exit.
Put the second casting side back on, including the nuts and pulley. When reassembly is complete, turn the motor pulley by hand. It should turn freely. Apply one drop of sewing machine oil to both ends of the motor. There should be a very small hole at each end. Apply another drop of oil to the shaft near the bushing. Wipe away excess oil. Before testing the motor, rotate the armature and shake the motor a few times. This helps position the small washers on the armature.
If the motor doesn't respond after plugging in the sewing machine and turning it on, the carbon brushes may not be well seated in the channel. If smoke appears, remove half the casting and clean the commutator with rubbing alcohol.