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Discussion Starter #1
Gentlemen,
I am currently working on my first diesel motor. It is in a 472.
I have gone through the reversing unit, cycles well, nice and shiny.
I have also gone through the motor, the only thing I dared not touch is the brass frame that holds the field coil. I have read too many posts on what a pain they can be to adjust right.
The motor runs one direction fairly well, maybe not quite as fast as I would imagine.
The field coil gets quite hot.
I does not run in the opposite direction, and I suppose if left on the field would get even hotter.
When in the no run mode I touched and wiggled each finger on the reversing unit with a toothpick, no movement from the motor. So pretty confident it is not the reversing unit.
I checked the commutator plates and the field coil with an ohm meter as per one of the posts, all seemed ok.
As usual, any help as what I might try next would be greatly appreciated. ( even if you think the field coil frame needs adjusting).
 

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Double-check your wiring. No mater if it's a diesel or steamer, usually when you run into this problem, the wiring is messed up.
 

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We need to go back to basics. The motor will not run in reverse for only one of two reasons There is mechanical binding in the reverse rotation direction or the reverse unit is bad. Regarding binding, it is unusual but possible. If there is current flowing through the field there is also current through the armature because these are series motors. A stalled motor connected to 12V will melt the enamel winding insulation in less than a minute releasing odor and smoke.
The far more likely cause is the reverse unit fingers and drum are not making proper contact in the reverse position. It is also possible someone rewired the unit and got the connections wrong.
 

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Discussion Starter #4
Runs great, thank you!
What I learned if interested:
With series type motors if it works in one direction then all the parts of the motor are working, i.e. the field, armature and brushes.
The reversing unit can still be a culprit.
As per suggested I set out to find a definitive wiring diagram for a 472, online, Aurotek and Barker resources. Between poor drawings, confusing descriptions I was totally confused. What helped most was Barker's current flow diagrams.
With that I made my own schematic, cut all the wires and reconnected in according to the flow drawing.
What I think I know now is that the reversing unit changes the direction of current flow only to the field coil.
The previous owner was a good solderer, but has crossed up field and brush wires.
Thanks again for experienced suggestions.
 

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What you discovered is correct, the reverse unit changes the direction of current flow through the field, leaving the armature unchanged. Series motors are relatively simple and if it spins in one direction the problem has to be a bad reverse unit, or as it took a lot of rework to discover, incorrect wiring by a previous owner. Great that you stayed with it to a successful conclusion.
 
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