Grinder Repair – Replacing the Armature (Makita Part # 515611-3)

Hi, I’m Mark from
In this video, I’m going to show you how to replace the armature in a Makita grinder. The armature is the main component of your grinder’s motor. It consists of the wire windings,
the commutator, the cooling fan and two bearings. There are several common problems or failures
with armatures, one of which would be burnt windings. When the windings overheat and get
burnt, it’s not uncommon to see burning on the wires themselves or the insulation around
the wires. A worn or damaged commutator is another common problem. Oftentimes, the commutator bar or more than
one bar will break away from the commutator. The cooling fan could be easily damaged if
a piece of metal or other debris gets into the grinder. It’s not uncommon to have several of the cooling fins or even all of the cooling fins torn away from the fan. If this occurs,
the motor won’t properly cool, and it will quickly overheat and cause damage to the windings.
And of course, any bearing will wear over time and need to be replaced. Replacing the armature assembly is easy to
do and I’m going to show you how. Armatures, as well as many other parts, can be found
on our website. Let’s get started. I’ll begin by removing the side handle and
the guard. The gearbox housing is held in place with four screws. I’ll go ahead and remove those. Now I can remove the rear
housing. It’s held in place with a single screw. Now I will move the brush springs to
the side of the brush holder. This removes the tension from the brushes so they are not
pressing against the armature. I will do this on both sides. With the tension removed from the brushes,
now I can go ahead and remove the armature assembly. Now I will remove the drive gear.
It’s secured with a nut. Now I will remove the front armature bearing and the gear housing
cover from the armature. To do that, I will place the cover in the open jaws on my vise.
Then using a rubber mallet, I will tap the armature shaft away from the bearing. Now I can install the gear housing cover assembly
back onto the armature. I’ll seat the bearing back on to the armature shaft using a socket
that has a diameter the same as the diameter on the inner-bearing race. Now I can reinstall
the drive gear and secure it with the nut. Now I can install the armature assembly back
into the grinder. I’ll reinstall the gear housing assembly to the motor assembly and
secure it with the four screws. Now reposition the brush spring back over the brush. Now
I will slide the rear cover back over the motor housing and secure it with the screw.
And I’ll finish up by installing the guard and the side handle. And now you know how to replace the armature
in a Makita grinder. If you found this video helpful, be sure to give us a thumbs-up and
leave a comment.

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