Postwar Pullmor Motor Short

This screw is not supposed to touch the tab under it. That insulated solder tab provides an important mechanical function... it provides a strain relief / anchor point for the field wire, and that's it. If it's shorted to ground, you will usually get operation in just one direction and a short in the other on a 2-position reverse diesel/loco.

That screw isn’t touching the tab, the issue is something else.

Well, you took it apart and then it there's a short that has developed.  I suspect you're going to have to revisit your steps and see where the issue developed.  This isn't the kind of issue that will be solved by guessing without any information.  Time to break out your meter and find out what happened.

Is there any place online where I can find some wiring schematics for postwar motors?

Art Legend

Go to the following link for wiring info.

http://olsenstoy.com/200alco.htm

Thank you!

@art_legend posted:

Is there any place online where I can find some wiring schematics for postwar motors?

Thanks for the help, after further investigation the short seems to be somewhere in the armature of the motor itself (all the wiring checks out). Not sure whether this is fixable or requires a new part(s).

I recently had a shorted out armature on a Marx 333.  You can test for a shorted coil with a ohm meter.  The resistance between adjacent coils that contact the brushes on the armature should all be the same ohms for good armature.  This can be checked by taking the brush plate off to see and probe the contacts, it is not necessary to remove the armature.

I bought a used armature with gear off eBay for $14, installed it and fixed the problem.  The seller would not ohm the used armature for me but said all parts come off running motors.  Beware of the number of teeth on the gear on a new armature as gears from some train motors may vary (they did on Marx 333 motors).  My seller had lots of parts for Marx and a few Am Flyer but not Lionel. 

Charlie

An armature may have very close resistance readings between each of the commutator segments and still have one shorted winding which will not show up on an ohmmeter. You need to also check the resistance of each winding to the center metal armature shaft. It should read infinity on all three windings. Any reading here indicates a shorted winding. To fully test an armature, you need a Growler.

If you suspect a bad armature, send it to The Motor Doctor for repair and rewinding.

Larry

Seems to be a shorted winding, thanks for the help!

Don't throw in the towel just yet.  If you were cleaning the commutator, you may have debris between the commutator segments, check that before you declare the armature defective.

I think this is a truck that suffers from misalignment between the upper and lower bearings. This results in the motor getting stuck.  This is an aluminum truck that is staked together and the staking comes loose. There is a lot of discussion on this forum about this problem.  Probably best to use search engine to see if you can locate information on this problem.  I think this is also covered in the service manual.  Applying power with the armature struck may result in condition similar to a shout circuit. 

He's got the brush-plate off and measuring the armature, I can't imagine this is a jammed truck.

From experience I suggest taking a toothpick and cleaning out the slots in the commutator, between the copper plates.  I have had conductive material (possibly a brush chip or something else) collect and short out.  Just as GRJ suggested.

Thanks for all the help everyone! David, I opened up the dust cover, I believe this engine was made after alignment was an issue (1962), as it doesn't appear that there are multiple bearings to align. I did however manage to clean some gunk out of the gearbox, wonder if some of that got ground up and worked itself into the commutator?  After cleaning the gearbox, the motor no longer hesitates to start up, but the motor seems to vibrate back and forth like there is indeed a short between the coils, which must be causing coils to power up when they aren't supposed to and locking the motor in place. Regardless, a replacement commutator isn't expensive, so I went ahead and ordered one to satisfy my curiosity. I'll try the toothpick idea, though previous attempts at cleaning haven't been successful at clearing the short.

Also forgot to mention, but there does indeed seem to be a short between the copper faces and the central metal rod.

If there is a short between the commutator and metal shaft, the armature is definitely bad. Replace it or have it sent out for rewinding.

Larry