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1920 M/G won't spin

Old buicks 2

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I had my M/G rebuilt and installed it on my 1920 K45 and it turned the engine as it should.   Now I have rebuilt the engine and installed the M/G and it won't even spin at all.    Battery is fully charged and unit it wired correctly.    What gives???????????   All connections are clean and bright,  starter cable is new  2/0 with soldered ends.   

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As you can see from the electrical circuit,  the starter and generator are on two separate circuits.  As Don said, when you press the starter pedal the generator brushes should lift off there commutator and the starter brushes lower onto there commutator. turning the engine.  If this is not happening, there is a problem with the raising and lowering of the brushes.  Get somebody to operate the starter pedal and watch to see if the brushes are operating. and engaging with their commutatlors.

When the ignition switch is turned on, the ammeter should indicate a discharge as the Gen brushes are in contact with their commutator.  Ensure the wiring is conected correctly, . Following circuit 3,  from the ignition switch to the coil terminal and then to the F ( shunt field) terminal. and the lower gen brush.  And the other wire from the ignition switch to the A terminal ( upper brush ) To create a closed electrical circuit.

1919 Buick electiric circuit.jpg

21-22 sg.jpeg


Edited by Rod Wise (see edit history)
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     Thanks for those wiring diagrams.  I did not have them. 



     I find this 1923-24 wiring diagram a little easier to understand because the ignition switch looks inside like the diagram.  There are 3 prongs on the ignition switch.  When the handle is rotated "ON", 1, 2 and 3 are joined by the spider contacts.    Use a volt meter or test light.  even a 12 volt test light will work if a little dim.  There are three 16 ga wires in your starter generator.  One is on the post with the battery cable.  Consider this power out.  The other 2 are power coming in to terminals A and F.  When the ignition switch is on, you should have voltage on all 3 wire connectors in the starter generator.   If no voltage on any of the 3 wires with the switch on, the problem is the ignition switch.  If voltage on all 3, then you have a brush or armature issue.     Hugh


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