How to Replace the Armature on a Porter-Cable Belt Sander
The armature is the central part of your belt sander's motor. It consists of the windings, the commutator, the cooling fan, and the drive shaft. The armature -- along with the field -- create an electromagnetic field that causes the armature to rotate at a high rate of speed.
The carbon motor brushes transfer electricity to the spinning armature through the commutator. Because it remains in constant contact with the carbon motor brushes, the commutator will eventually wear down. If the sander is overloaded, the armature can overheat, causing the insulation around the windings to burn away (creating a short-circuit). When this occurs, there can be excessive sparking from the motor brushes, and smoke (or a burning smell) from the motor.
Let's get started.
REMOVING THE ARMATURE
1. Remove the rear handle cover.
a. Remove the six screws that secure the rear handle.
b. Remove the rear handle cover.
2. Remove the front knob.
a. Remove the two screws securing the knob to the motor housing.
b. Remove the knob from the sander.
3. Remove the motor brushes.
a. Use a flat-blade screwdriver to remove the brush caps.
b. Remove the motor brushes from the brush holders.
4. Split the motor housing.
a. On the side of the sander with the exposed wiring; remove the two screws securing the two halves of the motor housing.
b. On the side of the sander with the belt cover; remove the three upper screws securing the two halves of the motor housing.
c. Pry the motor housing apart with a screwdriver.
5. Remove the belt cover.
a. Remove the screws securing the belt cover.
b. Remove the belt cover.
6. Remove the drive belt and pulleys.
a. Insert long-nosed pliers into the slots beside the (center) hex nut on the lower belt pulley. (This will prevent the pulley from rotating during removal.)
b. Use a hex wrench to remove the screw securing the lower belt pulley to the shaft. The hex screw is reverse-threaded (requiring clockwise rotation to loosen).
c. Remove the lower belt pulley (along with the drive belt) from the sander.
d. Grasp and hold the fan (opposite the drive pulley).
e. Use long-nosed pliers to grip and loosen the drive pulley.
f. Unthread and remove the drive pulley from the sander.
7. Remove the armature.
a. Tap the armature's drive shaft with a rubber mallet (from the pulley side).
b. Slide the armature assembly out of the field.
INSTALLING THE NEW ARMATURE
8. Install the armature.
a. Slide the plastic air guide over the new armature (this component fits between the armature fan and the motor).
b. Install the new armature into the field.
REASSEMBLING THE UNIT
9. Reinstall the drive belt and pulleys.
a. Thread the drive pulley onto the armature shaft.
b. Secure the drive pulley using long-nosed pliers (while holding the fan).
c. Install the drive belt onto the belt pulley.
d. Align the drive belt with the cogs of the lower (larger) pulley.
e. Install the lower pulley onto the spindle.
f. Secure the lower pulley with the hex screw. (The screw is reverse-threaded).
10. Reinstall the belt cover.
a. Install the belt cover.
b. Secure the belt cover with the screws.
11. Reconnect the two halves of the motor housing.
a. Before joining the two halves of the motor housing, take note of the following: The bearing on the inside of the motor housing should align with the armature shaft; the plastic air guide must be aligned with the mounting holes (on both halves of the housing); and the alignment pin should be visible on the front side of the motor housing (this alignment pin fits into both halves of the motor housing when assembled).
b. Join the two halves of the motor housing, verifying that all of the components (detailed above) are properly aligned.
c. Use a rubber mallet to tap the (bearing-side) of the motor housing to press the bearing onto the armature shaft.
d. Secure the (belt side of the) motor housing with the three screws. (The two longer screws install in the central part of the housing, and the shorter screw installs near the front knob.)
e. Secure the (fan side of the) motor housing with the two screws (these install under the handle cover).
12. Reinstall the rear handle housing cover.
a. Install the rear handle cover.
b. Secure the handle housing with the screws.
13. Reinstall the front knob.
a. Install the front knob.
b. Secure the knob with the two screws.
14. Reinstall the motor brushes.
a. Install the motor brushes into the brush holders.
b. Secure the motor brushes with the brush caps.