Troubleshooting a prewar O 252

Can you post a photo of the motor only on the brushplate side and the top of the motor? This will help.

here they are. Let me know if you need more.

A couple of things to check:

The wire connected to the field on the topside, be sure no wire strands are touching the post since it is so close to the motor frame.

Same with the wires at the brushplate screws.

Be sure the brushplate tubes are not touching the motor frame. Spacer washers may be necessary.

The motor looks identical to a 248.  To test the motor without a reverse unit, connect the field coil wire to the bottom brush.  Take the wire from the pickup roller and connect to opposite brush.  Take transformer and clip one lead to metal frame of motor, the other lead to the roller pickup.  It should run in one direction.  The wire connections on the brush plate cannot touch any metal of the frame.

Hi Chuck,

You were right! I removed the brush plate and saw evidence of arcing where the back of the brush tubes touched the frame near the armature opening. A piece of electrical tape solved it!

Now it runs VERY SLOW and has made it around the oval four times. It's well lubed and nothing is binding. The brushes appeared worn, but still had a good amount left. Lots of heat on the rollers. Would postwar brushes work in there?

I appreciate your help.

Thank you Teledoc. Your wiring suggestion is exactly correct! I appreciate your help.

I picked up a junk lot a few months ago, which had a 248 frame & motor.  Had to rewire it, and just need to replace the fiber gears, with brass ones.  Saw your motor, and realized it was the same as my 248.  

Bend the contact roller spring so there is more downward pressure on the rollers. Not enough tension will cause the rollers to get hot. Postwar brushes will work, but will need to be sanded to about 2/3 length as they will be to long otherwise. I would use the correct 1-92 brushes. The springs should probably be replaced too.

Right again Chuck! The engine is running smooth now.

i appreciate the help. 

Welcome.

Chuck Sartor posted:

Bend the contact roller spring so there is more downward pressure on the rollers. Not enough tension will cause the rollers to get hot. Postwar brushes will work, but will need to be sanded to about 2/3 length as they will be to long otherwise. I would use the correct 1-92 brushes. The springs should probably be replaced too.

Exactly right.  It's easy for the roller springs on the 252 to become distorted out over time (maybe kids were playing with them on the carpet?), and lose their tension.  When I restored my own 252, it would barely crawl around the layout, till I brought the spring pressure up to normal.