First thing to do is determine that the motor turns freely. If the wiring has been changed, you need to be sure the power goes through the armature, then to the field. The armature and field have to be in series. If there is an e unit in the circuit, on the four finger board, power goes in one side, usually black wire, and out the other side, usual green wire, to the field. The middle wire on the four finger board and the only wire on the two finger board, usually both yellow or one yellow and one blue, go to the brushes. On a single motor loco it does not matter which brush holder they go to. If the wiring looks correct check as best as you can that the side of the armature is not rubbing on the motor housing. I think on this loco that the armature is supported at both ends, not in the center. To keep the armature centered there may be steel balls in the brush plate and the lower bearing to handle thrust. Be sure those steel balls are in place. They are easily lost in disassembly. If all this looks to be good, next would be to use an ohm meter to check resistances. With the brush plate removed check the resistance between each copper commutator segment and the one next to it. There should be about 2 ohms of resistance and all three readings should be about the same. Then check from each of the segments to the shaft. The resistance should be very high, 10,000 ohms or more. If any of these resistance test fail, probably best to sent complete motor truck to Motor Doctor for repair.
let us know how it goes and include photos.
