How to Replace the Armature on a Worm-Drive Skilsaw

Is your saw producing a "burning" smell and sparking near the motor brushes? If so, you likely need a new armature. The armature is the central piece of your saw's motor. It works with the field to create the rotation needed to drive your saw. The armature is supported by bearings on both ends. One end has a commutator, which is where the motor brushes apply electricity. On the opposite end of the armature, the shaft is milled to accept the worm gear.

Under normal use, armatures are very reliable (and should last for many years with no problems). Eventually, the commutator will wear down from the brushes rubbing against it. Most armature issues are caused by overloading the saw. When the saw is overloaded, it draws amperage that is beyond what it was designed to handle. This causes the armature to become hot, and the insulation around the wire wraps will begin to melt or burn. Once enough insulation melts away, the armature will short out, creating excessive sparking around the motor brushes, a burning smell, and reduced speed and performance.

Let's get started.

REMOVING THE ARMATURE   1. Unplug the saw.

a. Disconnect the saw from its power source.

  2. Remove the motor brushes.

a. Rotate the lock lever to gain access to the brush cap.

b. Use a screwdriver to unscrew the brush cap.

c. Remove the motor brush from the brush holder.

d. Remove the second brush cap and motor brush (on the opposite side of the motor).

  3. Remove the locking lever assembly.

a. Use a screwdriver to pry the retaining ring away from the stud.

b. Remove the locking lever.

c. Use a wrench to loosen the acorn nut.

d. Remove the acorn nut.

e. Remove the spring washer.

f. Pivot the adjustment linkage away from the stud.

g. Remove the plain washer from the stud.

  4. Remove the motor housing.

a. Remove the screw that secures the upper guard to the motor housing.

b. Remove the four screws securing the motor housing to the gear housing.

c. Use a rubber mallet to tap the motor housing away from the gear housing.

d. Carefully separate the motor housing from the gear housing.

  5. Drain the oil.

a. Remove the oil drain plug.

b. Place an oil collection pan (or approved receptacle) below the saw.

c. Rotate the saw until the gear oil begins to flow from the gear box.

d. Drain as much of the used oil as possible in this way. This will limit the amount of clean-up required in subsequent steps.

e. Use adjustable pliers to loosen the bearing end plate.

f. Remove the bearing end plate and washer.

g. Rotate the saw to drain any remaining gear oil from the gear box.

h. Use a shop rag to wipe away any excess oil from the gear box and housing.

  6. Remove the armature.

a. Hold the armature with one hand and use a socket wrench to remove the armature nut.

b. Pull the armature out of the motor housing.

TRANSFERRING COMPONENTS FROM THE OLD ARMATURE TO THE NEW

  7. Remove the components from the old armature.

a. Remove the rubber O-ring from the (front) armature shaft.

b. Use a bearing separator to remove the (rear) bearing from the armature.

  8. Install the components onto the new armature.

a. Install the rubber O-ring onto the (front) shaft of the new armature.

b. Place the new armature on an anvil (or sturdy surface) with the rear shaft pointing toward the ceiling (or the sky, if you happen to be working outdoors).

c. Align the rear bearing (removed from the old armature) with the rear shaft of the new armature.

d. Position a socket (that has the same diameter as the inner race of the bearing) on top of the bearing.

e. Use a hammer to tap the socket and press the bearing onto the armature shaft.

f. Continue tapping the socket until the face of the bearing is flush with the armature shaft.

INSTALLING THE NEW ARMATURE

  9. Install the armature.

a. Slide the new armature into the motor housing. Rotate the armature (in either direction) as you install it, to align the splines on the worm gear with the splines on the armature shaft.

b. Secure the armature with the small washer and the locknut.

c. Reinstall the bearing end plate (and the washer).

REASSEMBLING THE UNIT

  10. Refill the gear housing (with oil).

a. Note: This saw requires "Heavy-Duty Worm-Drive Saw Lubricant."

b. Set the saw on its base with the blade extended as far as it will go. (This will help to keep the gear box level.)

c. Begin adding oil (through the drain opening) until the oil level reaches the top of the threads. (Add a little at a time, allowing the thick oil to spread evenly throughout the gear box.) Repeat this process multiple times (until the oil level remains consistent).

d. Replace and secure the drain plug.

  11. Reinstall the motor housing.

a. Install the motor housing onto the (gear housing) main unit.

b. Secure the motor housing with the four screws.

  12. Reinstall the locking lever.

a. Install the plain washer onto the stud.

b. Pivot the adjustment linkage onto the stud.

c. Install the spring washer onto the stud.

d. Install and tighten the acorn nut.

e. Install the locking lever over the acorn nut.

f. Test the locking lever for proper clearance, position, and functionality. Adjust and/or reposition the locking lever as necessary.

g. Secure the locking lever with the retaining ring.

h. Install and tighten the screw that secures the (upper) blade guard to the motor housing.

  13. Reinstall the motor brushes.

a. Slide the motor brush into the brush holder.

b. Compress the brush spring into the brush holder.

c. Install and tighten the brush cap to secure the motor brush.

d. Repeat this step to install the second motor brush.