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I've read dozens of posts with a few pictures but still can't tell how to test my armature.
I've cleaned it and see no burned spots but it appears shorted when assembled. I can't tell from the posts how to check for continuity on the long armature bars, the commutator, and shaft.
All of the long silver bars show continuity and all show direct continuity to the center shaft.
None show any short directly to any of the commutator copper bars.
All commutator bars show direct contact to each other but don't show a short to the shaft or the long armature bars.
 

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The armature is a simple winding with large wires. The windings are next to "0" ohms and that is why a growler test has to be done because of the magnetic info in the armature a non consistent armature will cause the growler bar to vibrate like mad and an indication of a need to rewire.

To make a growler is easy but a PITA, so bring that armature to a motor rewind shop and they are equipped to test it.

A simple home remedy is to hold a compass around it while power goes through, but a failing or failed armature will not pass current or in fact will pass too much, open or short. And by design these things can fail in either or both ways. The growler acts like a big compass.

Besides the windings shorting, burning the insulation could be failing and the winding open or just about open,. The commutator is the junction of these windings and allows rectification by its action and by the brush contact and the bars could easily be shorted by heat. There are many things that can go wrong with higher than normal heat and it takes testing as you know to find these things out.

Heat marks like blue tinges, carbon marks or copper that is dark are not always the case, but steel bluing at the armature ends can harm bearings. The perfectly round and balanced armature can be out of round and lob sided by uneven distribution of molten solder and high RPM throwing that solder out. When this happens the commutator becomes a mess, shorted, open and the motor or generator aspect of that armature is just a dead weight.

Even if you know what is wrong the fix is not easy. The armature is a wonderful device when working but to actually repair takes high heat and time as you break it down, burn it apart and start over the process of rewinding all by hand with the help of a lathe to wind the winding(s), in a starter they are bigger wires with fewer number of windings.

Because of the technique and expertise and time and patience, not to mention the soldering and balancing a destroyed starter is best left to a rebuilder with the equipment, the knowledge who will pay for the base core and supply you with a rebuilt starter.

And don't forget the paper work! Every rebuilt starter comes with a document stating the test results that you must read before buying.
 

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Check for continuity between pairs of copper commutator bars . There should be continuity.
Check for cont. between commutator bars and armature shaft.
There should be no continuity.
Check for discoloration between pairs of commutator bars , if ok your armature should be ok.
Check for dirty and sticking brushes.
Please define " seems like shorted when assembled " ?
 

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It shows the main starter hook up lead post shorted to the case when assembled. I tested during assembly, and no short until the brushes were installed then it show a short. I read in another post that the commutator bars were only supposed to have continuity to another bar partway around, but not to each other. All of my commutator bars show continuity to every bar all the way round, so I'm guessing it shorted internally. It would make sense I guess that only commutator bars in pairs are joined as the shaft rotates from one to another but mine all show continuity to each other as a whole, although not shorted to the shaft or armature
 

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Steve, if your meter didn't show low or no resistance between the positive post and the frame the starter would not work.:shock:

Every segment of the commutator is connected to every other one through the winding's and the long bars between the winding's are part of the shaft assembly so it's normal for them to measure shorted to the shaft.
 

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This may help you to understand. The armature is a big one and you know what they say about pictures.

http://weldingweb.com/showthread.php?t=33897

copy and paste the above line into the address line of your browser.
 

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The thing with measuring a short via a multimeter is critical with respect to the equipment you are measuring on.

The armature is a short winding with a large conductor and the armature is relative to the field in which it spins. Both the field and armature are in series, so the amperage through each, the field and the armature is the same....

but the amount of amps is drastically altered when the armature is spinning compared to when the armature just starts off from a stop. This is true of the testing, the armature will indicate low resistance but it has high reluctance. It is a magnetic device.

From a stop to a start of spinning the armature and the field take on a massive amount of amps that are reduced as the spinning starts and grows because of counter emf, electro motive force. This force counter acts the forces that cause rotation. The reason all motors left to their own draw a lot of amps to start with. Compound parallel wound motors can be controlled and brought to rotation by easing the amp flow. Series wound motors are made to be overloaded to do their job, starting a cold engine.

But because the DC series wound motor as it sits stopped and it is a relative massive size of copper measuring ohms to ground or ohms to another part of the winding, the commutator bar will indicate a low number.

With a 0, zero, we usually know there is no resistance but these motors can exhibit a low number .5, .4, .3, .2, .1 ohms and not be shorted because their resistance is inherently low and there real effect is counter emf that requires moving rotation and another counter effect of the load of the engine they are trying to start.

Each motor has a real number of ohms in resistance and as the motor becomes larger and larger that actual ohms number gets smaller because of the larger mass of copper.

A shop can test for a short but still a dynamic test is used to verify the preliminary test. The same as testing a 12 V starter motor without a load attached. The test will indicate if basic power on, motor should turn, but it does nothing to indicate if the motor develops the torque, HP and grunt force to do the work its designed to do.

And because series wound motors are grunt force movers they get hot so hot that they can burn themselves out if over used. DC energy likes to travel within a conductor. DC energy creates massive amounts of energy in the form of heat that is located deep within the motor and the core is a massive steel and copper that retains this heat. At some time there is so much heat retained that it melts insulation, solder and removes the magnetic affect of electron movement through the windings and because of short circuits creates more heat to ground or to the shorted parts. All this massive energy going to shorts/grounds creates a mess.

This mess now cannot rotate, cannot use its magnetism, just its lack of resistance to heat things up.
 
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