Well if this small stuff don't beat all.
Got to looking at that twin motor ALCO 200 series B-unit I built today to see why the one motor is shorting out. It had a bunch of up and down play in the armature and I thought it was just plain worn out. It would run fine going in forward ( armature pushing up because that motor is facing backwards ) but when you would shift it to reverse (armature pushing down) it would short out. So I pulled the brushes and armature out and tried it and it ran great. Well then I thought WTH??
I got to looking at the armature and saw ever so small rub marks on the bottom of the winding and looked into the field frame and saw small rub marks on the top of the frame. Knowing this is a 1957 200 series alco motor I thought I should check for the small ball bearing ( 600-110 ) that goes in the plastic lower armature holder and guess what was missing?
I had another plastic lower holder from a 1957 202 and took out that ball bearing and put it into the motor I was working on and BINGO!!! Works great. 
Now what to do with that replacement motor I bought on e-bay last week?? 
Maybe build the second A unit so I can have the ABA set? 
