Pulmor Motor Question

I gave up on Pulmor motors years ago, and it's problems like this that remind me why. 

A couple things you could check. Look at the brushes and make sure they aren't worn unevenly or at an angle. If you've been running it one way for a long time that can happen. Also check to make sure that there isn't a carbon buildup between the commutator segments. 

My experiencewith lastly with larger DC motors, but I think you have diagnosed your problem correctly.  The problem is a defective armature.  The E unit reverses the polarity on the armature.  If there is a ground on the armature windings, the motor may run when the grounded winding and the frame are at nearly the same voltage.  But when the E unit reverses the polarity of the armature, the grounded winding to frame voltage is high the motor will not run.  

I have rewound these armatures in the past, but it is not fun.  There are people out there who will rewind the armature for you.  Replacement armatures are available for most of the Lionel motors at a reasonable price.

I have one and my experience has not been good like yours. A local repair guy ended up using a combination of old postwar and new postwar style parts to get my unit to work properly and even then he advised keeping the run hours low since he did not know how long it would run. Apparently there are brush plate and bottom bearing alignment issues that cause the armature problems.

Please let us know what you do to fix it.

Did you try reading to the armature shaft from each of the commutator sections?

I had a motor that would only run in one direction. In my case, the motor needed a new armature, and I installed the wrong one. The alignment between the commutator segments and the poles was wrong.

It is not common, but on some modern era motors, the commutator can twist (slip) on the armature shaft.
Still, if you had a misalignment problem, I would expect the motor to act the same on all three poles.

I tend to agree with Elliot above. Check/replace the brushes, brush springs and clean the commutator and gaps. There's no harm and little expense in doing such, and it could well solve your problem. 

By the way, the Original Poster wrote that he "checked the continuity".

The resistance should be checked between each pair of segments, and between each segment and the shaft.

The resistance between each segment and the shaft should be infinite.

The resistance between segment pairs should be consistent between all three pairs, The Hannon book gives the armature resistance for the postwar version as 1.1 to 1.2 ohms. I expect the modern era armature would have similar values.

Again, its odd that the problem would only present itself when running in one direction.

Normally, problems running in one direction tend to be mechanical in nature like thrust bearings and the like.

Thanks for the ideas so far.  I had cleaned the armature surface and the slots.  One brush was hanging up in the holder which I already corrected.  Since this is a tmcc loc, there are caps installed on the brush holders.  I thought maybe a cap shorted out since they go from the brush holder to ground.  I disconnected the caps and it made no difference.

When running forward, I put my finger in the way of the armature and confirm each pole wants to rotate past my finger.  There is significant force.  In reverse, two of the poles give force and then when it gets to the third pole it stops and buzzes.

I did check the armature with my meter and I get no readings (infinite) from the commutator segments to the shaft.  I get a reading of about 1.2 between each segment.

With power off, I can rotate the armature with ease forwards and backwards.

It has all the indications of a bad pole in the armature except that it works in one direction.  If the pole was bad, I would expect the same problem in both directions.  When it stops in reverse, the brushes are each on a complete segment (not between segments).

Are the brushes tilted, loose in the brush holders, or are the brush ends slanted? Is there a weak brush spring?

There could be a burr on the commutator that is hitting a brush in a certain way in one direction only. If you can get the motor in the "stall" position, then touch the brushes with a toothpick, maybe something will be revealed.

It is not common, but on some modern era motors, the commutator can twist (slip) on the armature shaft.
Still, if you had a misalignment problem, I would expect the motor to act the same on all three poles.

How can I tell if the commutator slipped?  How should the commutator segments line up with the poles?  I have some postwar locs I can take apart and compare the armature.  I assume the commutator would have to be in the same position for all armatures.

quote:

 I assume the commutator would have to be in the same position for all armatures.

Unfortunately they are not in the same position for all armatures.
I thought they were all the same until I ran into the problem that I mentioned in my first post in this thread. (confirmed in Hannon's book)

Assuming the modern era armature matches the postwar one:

According to Hannon's book, the slot between two commutator segments should be in line with the edge of the metal pole right where the slot ends.  (my description)

If you have a gang car, you can compare your armature to the gang armature for the slot position.

The following postwar locomotives all use the same armature, #41-40:

41, 42, 51, 53, 55, 56, 57, 59

This sounds more like a mechanical issue than electrical...If you where to mark the side of the afmature where it stops, I would bet it is not the same pole every time...When you change directions, does the armature move up and jam???  Because this problem is very common and usually a spacer washer has gone bad and is probably missing...Does this engine have an adjustment screw on top of the brush plate. The armature when it changes direction should only move at 1/16 of an inch....

Marty

As Marty said, and I said previously, I think this will turn out to be mechanical.  Running the motor with no load is quite different than running it under load.  Specifically, the armature will be forced to the opposite bearing for the reverse direction, this is normally where the problem surfaces.

I have to admit  that Marty and John are probably correct.

It stops on the same pole every time.  I know this because 2 of the poles are wrapped in red coil wire and the third pole is wrapped in green coil wire.  It always stops when the green pole is exposed.  The armature is held in place by a set screw on top of the brush plate.  The set screw presses down on a ball bearing on top of the armature shaft.   I don't see the armature shifting up and down at all when it runs.  The only thing I see move a little is the gear attached to the wheel axle.  That gear shifts slightly when it goes into reverse and shifts back slightly going forward.

When it gets stuck, I can turn the armature enough by hand and it will spin past the 2 red poles and stop again on the green pole.

Keep the ideas coming as I check on everything you guys offer to see if I missed something.

This sounds like a bad gear, shouldn't move....Is it a nylon gear???

Marty

Its a metal gear pressed onto the axle.  The whole axle will shift along with the wheels.

For grins, I turned the armature by hand (with the power off) and set it so the green pole was exposed.  I then applied power.  The armature just buzzed and it did not move at all.  I had to manually move past the green pole and then it starting moving.

You just might have a bad armature, especially since it is failing in the same place.   I don't suppose you have another you can swap out and try???

Marty

Loosen that setscrew about one turn and see if anything changes.

ALso do you have the item number, want to locate a parts list on lionels web site...

Marty

I'll see about getting another armature.  Still its odd that it works in the other direction.

Tried adjusting the set screw - no effect.

I don't have a spare one or I would try replacing it.

 Some how I feel your problem is gear related, and not armature, also you say its TMCC, I would check into that.

Rod

Could well be gears, I can't get it out of my head that this is mechanical and not electrical.

Check the spur gears on the side of the power truck. If the gear shafts are worn, or the gear mounting hole worn, the gears can 'cock' resulting in uneven wear. Eventually this gets to the point where they may jam, most often in one direction but not the other. I've seen this a few times in my shop.

I had a similar problem once a long time ago, don't remember if it was a bumper car or the trolley but the problem turned out to be a worn brush plate. The hole for the armiture shaft was ovaled just enough to allow one of the armiture poles to contact the field when turning in one direction but when rotating in the other direction would rock back enough to allow proper clearence. The key was that it would act up at slow speed but would make noise when running at high speed. Inspection of the inside of the field poles showed a slight buffing of the laminations where the field was hitting. That was the only time I ever ran accross this problem.

Al

When checking the brushplate also check the armature bushing that is mounted in the frame and the thrust bearing.

Bill 

I will check the brush plate for wear but I doubt it.  I bought it new when it came out and its seen very little run time.  Side gears look good as do the bushings for the wheel axles.

If the brush plate is plastic (which I suspect), check to see if the end of the armature shaft that goes into the brush plate has any plastic residue; sometimes heat from the armature shaft (due to brush plate friction) will coat the armature shaft with this residue. Polish the armature shaft that goes into the brush plate (I use scotchbrite) and coat with a very small dab of  grease (I use Lucas Tacky Red). I run into this on these plastic brush plates with set screws.  You may also try another brush plate; OR, the axle gear may be a bit off center; you mentioned some movement with change of direction; should be centered for equal movement with change of direction. Just my experience based on Pullmor "scar tissue". Good Luck, Falcon70