I just took a working starter motor halfway apart. I know, "if it isn't broke"..... Well it was so caked with dirt & grime I couldn't see the brushes & holders inside the cover and looking at those two field wires it would be 'broke' soon anyway.
The two field coil wires had no insulation left, just old falling apart electrical tape (see photo). After cleaning all the gunk out and installing new insulation covers on the two field coil wires, I have a small problem. Which 2 of the 4 brush terminals do those two field wires go? They are both black so I can't tell them apart (if I need to) and I'm not sure how they are routed inside the cover to stay out of the way of the moving parts. I have the F.S.M. but it's not helping me much.
I'm not a half bad machinist or home mechanic but in the past I just took starters & generators to a shop.
Second, anything I should know about testing the starter on a workbench before I re-install it?
James
Look closely at the four brush holders in the cap and you will notice two of them still have brush holder screws connecting the brushes and two do not have screws. Reinstall the cap and connect the two field pigtails to the two brush holder with no screws. When the cap installed the pigtails only reach and can be connected one way and it it is literally impossible to connect them wrong.
Connect a 6 volt battery to it and be careful it will almost jump off the bench from the high torque.
Though it requires some special test equipment a properly working Model T starter will draw 70 amps free running and push 12 pounds in a stall torque test.
You did not ask this question, but while you in thee I would refinish the commutator and install and seat new brushes. And make sure the terminal bolt to buss bar connection has not been damaged. Move the bolt with your fingers and look at the connection closely, if it is broken you will see it. If it is damaged, clean the connection carefully, you will need a 250 Watt soldering iron and some silver solder.
I rebuild Model T starters every day and if you need further help give me a call.
Ron the Coilman
859-881-1677
Looks like it's time to replace the rear babbitt bushing too.
I believe the T uses copper brushes. With copper brushes you do not under cut the separator when machining the commutator as you would do on machining a generator armature. I have noticed that now days most automotive machine shops do under cut the separator on starters. I assume this is due to starters now using carbon brushes. Correct me on this if I am incorrect.
Rebuilding Model T starters is a slippery slope.
Ron the Coilman
Cecil if you are talking about undercutting armatures (between the bars) it is seldom done. Most have molded comms.
That is to say modern stuff not vintage; noting the words 'now days.'
Molded comms have very little copper and are basically glued together. Undercutting weakens the structure.
Ron said it best.
Id replace the babbitt bearing with a new sealed bearing. Are the insulators in the brush plate good? Is your armature shaft straight? Is your snout straight? Is your snout bushing wore and needing replacement? If you replace the snout bushing, is it bored out so as to align the bushing and bronze bushing? So on and so forth, a very slippery slope.