Motor Repair

Motors are important components to hundreds of devices we use in daily life. This Fix-It Guide on motor repair tells how a motor works, what often goes wrong, how to identify a motor problem, and what parts and tools you will need to fix it. It then gives simple step-by-step instructions for how to test an appliance motor, how to service a motor’s drive mechanism, how to service a motor’s gears, and how to service a motor’s fan blades. (You can order replacement parts at FixItClubParts.com.) Motor repair may be needed to complete electric saw repair, floor polisher repair, food grinder repair, power tool repair, slide projector repair, small appliance repair, and more.

How Does a Motor Work?

A motor turns electrical energy into motion. Actually, it uses electricity’s magnetism to attract, then repel components to rotate a shaft. You can attach fan blades, knife blades, wheels, or a dozen other components to the shaft to make useful devices. To name a few: blender, cassette deck, CD player, coffee grinder, computer fan, computer printer head, DVD player, electric can opener. . .you get the idea. These and hundreds of other functional gadgets rely on electric motors to give them motion.

Smaller appliances typically use what’s called a universal motor. It’s simple, efficient, and relatively inexpensive. It’s called “universal” because it can run on either alternating current (AC) or direct current (DC) power. The part that stands still is called the stator and the rotating part is the rotor. It’s as simple as that.

Some small appliances use a variation called the shaded-pole motor. It works about the same as the universal motor, but is less expensive to manufacture so it typically goes into lower-cost, low-load, small appliances.

Larger appliances, as you can imagine, require more power. Many use a split-phase induction motor to develop more rotating power, called torque, than smaller motors can muster. Split-phase induction motors, too, have stators and rotors.

Smaller things, such as battery-operated appliances and tools, get their power from DC batteries so they are made to run on direct current. They don’t have much motion or torque, but they get the job done in a small space.

motor1 Motor Repair

You can see the commutator and the rotor inside this motor from a variable-speed food mixer.

What’s the difference? Usually it’s cost. Most manufacturers use the least expensive motor that does the job. Fortunately, checking whether a motor runs or doesn’t is about the same for any type of motor. Unless you’re adventuresome, you probably won’t dismantle a motor and replace components. If it works, you’ll use it; if not, you’ll recycle it.

Many motors include a drive mechanism of some type that transfers the shaft rotation to some other component. You can fix or replace drive mechanisms as well (see below).

What Can Go Wrong with a Motor?

motor2 Motor Repair

Turning on and off the motor’s brushes (left, top, and bottom) creates a magnetic field that makes the motor shaft rotate.

Though efficient, motors can work against themselves. A small problem can become a big one quickly and, soon, the motor is damaged beyond repair. Fortunately, most motors will tell you–sometimes subtly, sometimes not–that they are having problems. Motors burn out and freeze up; they get noisy, overheat, and wobble.

Fix-It Tip

Hearing noises that may be a motor going out? Turn off the appliance immediately. It may be something rubbing against the moving parts or it may be a problem in the motor itself. In either case, the faster you catch it the easier it will be to troubleshoot and fix it.

How Can I Identify a Motor Problem?

  • If gears on the motor shaft wobble, the bearings may be worn out or some of the moving parts may be misaligned.
  • If you see sparks inside the motor, the rotor, stator, or brushes may be worn or damaged.
  • If you smell a mild odor of hot oil, metal, or plastic, the motor is overheating and may require lubrication.
  • If you smell a pungent, acrid odor, the motor’s windings may be damaged.
  • If the motor is too hot to touch, something may be blocking ventilation around the motor.
  • If the motor makes a grinding noise, bearings may be worn out.

Fix-It Tip

Parts inside a motor rotate, so they require lubrication to minimize friction. Some motors have holes on them marked oil where drops of lightweight oil can be added. Other motors have hard-plastic bearings that don’t require lubrication but may eventually wear out after years of use. Check the owner’s manual for your appliance to determine what regular service the motor requires.

What Do I Need for Motor Repair?

If you have electrical experience and some advanced tools, you may be able to repair a motor yourself. However, most consumers opt to test and, if necessary, replace the motor. You can buy one through the appliance’s manufacturer or an aftermarket supplier.

Once you’ve disassembled the appliance (see the appropriate Fix-It Guide), here are the tools you’ll need to test an electric motor:

  • Screwdrivers
  • Wrenches (standard and hex)
  • Multimeter

What Are the Steps to Motor Repair?

Test an appliance motor:

  1. motor3 Motor Repair

    This hair dryer motor and fan can be tested easily using a multimeter.

    Make sure that the power cord wires are disconnected from the motor. If it is easy to do, remove the motor from the appliance, though motors can be tested in place.

  2. To test continuity (the flow of electricity) through the motor, set the multimeter on the RX1 (resistance times 1) scale to measure resistance (in ohms). The multimeter’s internal battery will send a small electrical current through the motor’s wires.
  3. Attach one of the multimeter’s probes to the motor’s common lead, usually white.
  4. Attach the other probe in turn to each of the other wires on the motor. The probe will check to see if it can measure the multimeter’s input signal at the output. A low or moderate reading (in ohms) means the component is okay. A zero or infinite reading means the motor’s windings or another component has a short.
  5. If it tests faulty, replace the motor with one of the same type, power rating, and size.

Service a motor’s drive mechanism:

  1. Tighten the setscrew that attaches the pulley or collar to the shaft.
  2. Adjust the drive belt so it is not so tight it wears out the shaft nor so loose that it doesn’t rotate with the pulley. If the belt is worn or damaged, replace it.
  3. Check and tighten or replace any reduction or worm gears on the shaft. Gears typically come in pairs and should be replaced as pairs.

Service a motor’s gears:

  1. Disassemble the appliance to access the motor’s gears.
  2. Remove and inspect gears for obvious damage or wear and replace as needed. Gears, especially, are susceptible to damage because many are made of plastic that can break or chip.
  3. Reassemble and test.

Service a motor’s fan blades:

  1. Disassemble the appliance to access the motor’s fan blade.
  2. Remove, inspect, and repair the fan blades. If not repairable, damaged fan blades should be replaced because they can spin unbalanced and potentially damage the motor.
  3. Reassemble and test.

Fix-It Tip

Install a new motor or reinstall the old motor in the exact same way as it was removed, making sure that all wires are connected as they were originally.

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