American Flyer Testing Double motor diesel armature

With an ohmmeter set on low ohms, you can test each copper commutator section to the others. The readings should be within a few tenths of an ohm to each other. Then test each commutator section to the central metal shaft. There should be an infinite reading on each section.

These tests will tell you if the windings are not severely shorted or open. If the armature passes these tests and the motor will not run, the armature may need to be taken to a facility that rewinds commercial armatures and have them check it with a 'growler'. That will give you the final answer if the armature is good or not.

The Motor Doctor rewinds and rebuilds model train armatures.

Larry

When you take the measurements Trainlarry described each one should measure 1.9 to 2.0 ohms.

What makes you suspect a problem with the armatures?

Hard to believe both would be bad . Need to secure one brush away from armature on one motor & test one motor at a time . Use jumper wires & by pass e- unit .

Bob G.

Could we be looking at the standard problem being the reverse units fingers and drum being dirty?

Absolutely !!!!

Bob G.

I'll answer all the suggestions Readings on my ohmmeter 1.9 & 2.0 The other  commutator to the shaft is infinite. I tested the motors separately assembled.  bypassing e-unit .  field to brush,  field to hot .brush to ground.this test works fine on steam engines. On this test I bypassed the e-unit, even though I installed new contact fingers and cleaned the drum. Sometimes I could get the motor to run, but than it would stop.  I than turned the armature a little and some times it would start and than stop again, I thought maybe I had a dead spot on the armature. But not likely with 2 motors. My next thought was the try to adjust the screws    s-o on the field clamp assembly. Even though I never had to adjust them before. Any more thoughts will be appreaciated Thanks again

You should be getting 3 readings between 1.9 - 2.0 ohms between any 2 of the 3 commutator segments.

You should get an infinite reading between each commutator segment and the steel armature shaft.

Larry

From your description of the test results obtained with the reversing unit bypassed the most likely cause of intermittent running is the brush assembly and brush springs. The lever style springs need to apply strong pressure on the brush holders and be carefully aligned. This was a marginal design and is the first item to suspect after the reverse unit is properly working.

I would not mess with the field centering at this point. If it is slightly off the motor might run slow but until the brushes, arms and springs are all correct it is premature to change the field centering.

Tom is right, I have had lots of occasions when a diesel fails due to the wires soldered to the brushes causes them to lose tension. I wonder if after all these years the insulation on the wires has hardened with age which makes it less flexible.

I seem to remember that if the wire passes through a hole next to where the brush pivots, this can cause the brush to just lift or reduce tension to the armature.

If this is the case then you can unsolder the wire and pull it back out of the hole and resolder it on and not use the hole to route it.

Another solution is to possibly remove several inches of each brush wire and splice in some new more flexible stuff.

I had one a few weeks ago that was intermittent& after hours of checking I had it laying on it's side & noticed arching between  the brush & the brush lever . Touched with hot iron & fixed the problem .

Bob G.

The other thing I have noticed about diesel chassis that have not been run for a long time and fail, is to remove the side frame assembly and apply power and then Just gently squeeze the two brushes against the armature and hopefully they burst into life again. I suspect that not being used for a long time frame that you get some form of oxidation between the brush and armature which stops voltage/current flow.

It seems that of all the problems that diesel chassis give us, is that ACG succeeded in inherently building in as many problems as possible and they did it in style.

I agree with the above post .

Bob G.

The ongoing saga of the double motor 470. Engine runs on test stand (both motors work, e-unit sequences f-n-r)  When I put on my track The front motor doesn't always start, the rear motor works, a few tries working the rev, unit the front motor kicks in and both work. I can't get both motors to start consistently. Once both are running if I stop, the same problem. Both motors are running in the same direction.  Things I've done armatures test in the 2.ohm range, & infinite. New brushes, Cleaned drum & put new contact fingers in rev. unit. Checked wiring schematic, Changed a few suspicious wires. Checked solder joints. Cleaned wheels. track. Need more suggestions Whats left?

Almost sounds like excessive axle wear. Is the test stand exerting upward pressure on the wheels and axles?

Broken wire making intermittent contact?

Finally the solution richabr suggested axle wear. Changed out wheel & chassis assembly that did the trick.  I want to thank all the guys who gave me input.  Process of elimination. We learn something every day. Thanks again to all

Get it rebushed and you've got a trusted replacement!

When re-bushing a diesel chassis you also need to see how badly worn/scored the journals are on the axles. If you put worn axles back  in they can easily and quickly chew out a nice new bearing and you are back to square one. You really should use new axles after a chassis rebuild.

Project for Jan. Finding a source f/bushings & axles. maybe Port lines or Leventon. Thanks for the tip & Happy Holidays to all