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It's a pretty straight forward rebuild. You take it apart and replace the brushes that ride on the commutater. Just have it on the bench and take off the front and see how things go together. You will see the worn out brushes , replace them and clean up the area they ride on with a scotchbrite pad.
 

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sunsetdart said:
It's a pretty straight forward rebuild. You take it apart and replace the brushes that ride on the commutater. Just have it on the bench and take off the front and see how things go together. You will see the worn out brushes , replace them and clean up the area they ride on with a scotchbrite pad.
That might work on a generator that shows little or no wear on the commutator and where the windings have not shorted out.

The armature should be tested on what is called a "growler" first. This will determine if any of the winding is shorted out. If it is shorted out, then the armature will need to be re-wound. The next test is a 'bar to bar' check with an ohmmeter. This is a check for shorts between the commutator bars. If this also checks out OK, then the commutator can be turned. This is done in a lathe. The mica between the bars should also be undercut the same depth as the width of the mica. The mica is also removed from the sides of the bars in the undercut slots. The edges of the bars are then chamfered slightly and the commutator is then burnished. For small automotive size armatures, balancing is not usually required. For larger diameter armatures, dynamic balancing should be performed.

Bearings should be replaced and new brushes installed. The brushes should also be 'seated' to conform to the diameter of the commutator. This is done by placing sandpaper around the diameter of the commutator (one layer with no overlap) while it is installed in the generator housing. Then the brushes are installed and the armature is spun by hand a few revolutions. This will sand the face of the brushes to conform to the diameter of the commutator. The sandpaper is then removed. The generator can then be installed.

All of the above is also correct for any electric motor that has a commutator.

Undercutting is NOT done on starter motor armatures. That is because the brushes used in starter motors have a high copper content rather than just carbon due to the high current draw and thus negating the need for undercutting.

NOTE:

It is VERY important to polarize the generator before starting the engine after the generator has been worked on. Even if just the brushes have been swapped out. If this is not done, the armature and/or the regulator can burn up.
 

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Discussion Starter · #4 ·
polarize

Frisco said:
That might work on a generator that shows little or no wear on the commutator and where the windings have not shorted out.

The armature should be tested on what is called a "growler" first. This will determine if any of the winding is shorted out. If it is shorted out, then the armature will need to be re-wound. The next test is a 'bar to bar' check with an ohmmeter. This is a check for shorts between the commutator bars. If this also checks out OK, then the commutator can be turned. This is done in a lathe. The mica between the bars should also be undercut the same depth as the width of the mica. The mica is also removed from the sides of the bars in the undercut slots. The edges of the bars are then chamfered slightly and the commutator is then burnished. For small automotive size armatures, balancing is not usually required. For larger diameter armatures, dynamic balancing should be performed.

Bearings should be replaced and new brushes installed. The brushes should also be 'seated' to conform to the diameter of the commutator. This is done by placing sandpaper around the diameter of the commutator (one layer with no overlap) while it is installed in the generator housing. Then the brushes are installed and the armature is spun by hand a few revolutions. This will sand the face of the brushes to conform to the diameter of the commutator. The sandpaper is then removed. The generator can then be installed.

All of the above is also correct for any electric motor that has a commutator.

Undercutting is NOT done on starter motor armatures. That is because the brushes used in starter motors have a high copper content rather than just carbon due to the high current draw and thus negating the need for undercutting.

NOTE:

It is VERY important to polarize the generator before starting the engine after the generator has been worked on. Even if just the brushes have been swapped out. If this is not done, the armature and/or the regulator can burn up.
what is polarize mean
 

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bigrobdog said:
what is polarize mean
It is a method to assure that the current flowing thru the generator and regulator is going in the correct direction for the vehicle.

To polarize the system: Before cranking up the engine, hold (do not permanently connect this wire. Just hold it in your hand) a jumper wire from the 'B' Battery terminal on the regulator to the 'A' armature terminal on the regulator for a few seconds. Remove the jumper wire.That's it. Everything is completed. The system is now polarized.


This is why the system needs to be polarized:

Many early 6 volt systems were positive ground. Some were negative ground. Some later 12 volt systems were also positive ground. Today most are negative ground.

When a DC generator has been taken apart to be inspected and/or worked on, there is a possibility of the polarity being reversed. To insure that the generator matches up with the vehicles system, the armature/regulator must be "polarized" with each other. This is done very easily and simply. See instructions above.

Connect all the wires in the correct location. From the generator to the regulator it is 'A' (armature terminal on generator) to 'A' (armature terminal on regulator), then 'F' (field terminal on generator) to 'F' (field terminal on regulator). The main body of the generator is grounded to the engine. The outer shell (body) of the regulator is grounded to the body thru the mounting bolts. There is a #10 gauge wire that goes from the Battery 'hot' terminal to the 'Battery' terminal on the regulator. The connection at the battery will depend on whether you have a positive ground or negative ground system.

SEPARATE NOTE:

Systems that use an alternator do not need to be polarized. An alternator produces AC (alternating) current. This is changed to DC (direct current) by diodes inside the alternator.
 

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Frisco has a very good write up on rebuilding generators, but I guess that I would like to suggest that now might be a great time to swap that 15 pound block of iron and copper to a nice 65 amp alternator.

Dave W
 
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