Problem with Atlas/Kato motor performance

[GGNInNScale]

I had a big issue with a reworked Atlas/Kato GP diesel.  It is old, but... Anyway, I searched out the 2017 thread for ideas.  Tried a few things- lube, remove the inner bearing, etc.  Then I started pushing the plastic motor retainer frame.  Voila!  It turned out that the frame had warped a bit over time and the rear flywheel touched the frame.  It was slight, but enough to stop rotation until about 8 Volts at 350-400mA draw.  So, I put a couple layers of Kapton tape between the frame and the metal main frame at the rear area, along the bottom of both sides of the frame.  Now, it starts at 1.5V unloaded at 70mAmps.  At 6V it is pulling ~90mA.  Putting in the gears and one bushing- pulls about 94mA.  Fully assembled it pulls 135mA at 6V in Reverse, and 117mA in Forward.  Progress! So, this might be something to look at when the performance degrades. I ran 5 minutes of breakin in both directions, no change in current draw, so I figure I got the bugs out.

[u18b]

What does "reworked" mean?

Maybe I'm wrong, but it is honestly hard to imagine that Kato or Atlas would make a motor with the flywheel too close.   Is it possible this was a problem created from tinkering and re-working?

Just curious.

And thanks for the post.

[peteski]

Interesting problem and solution.  Which specific Geep is  it?

I'm with Ron. While I have heard of "zinc rot" (which can deform them) in frames from other manufacturers,  I have never heard of Kato-made frames deforming by themselves. Only of they were subjected to physical damage (like being dropped or bent).

Is it possible that the motor and flywheels came from a different model? Or is it possible that the rear frame spacer/insulator is squished, allowing the frames to tighten closer together?  But I would thing that would also cause the truck to bind while swinging to the sides.

[thomasjmdavis]

Thanks for posting. I haven't encountered that particular issue but good to have some guidance if I ever do.
I assume that the loco in question is a GP-30 or 35, since mention is made of flywheels, which the Atlas-Kato versions of the GP 7 and 9 did not have.  Would I be correct that the "plastic motor retainer frame" is what Atlas and Kato called a "motor saddle"?  I could certainly see that part deforming over 30 years- especially if the motor ever overheated, or enough crud built up under the flywheel to cause a lot of friction.
I'm having a bit of a problem envisioning how the kapton tape is being used- photo would help.  I have a number of older units and like to keep track of this sort of "fix".

The Atlas/Kato GP-35 courtesy of Atlas:
https://download.atlasrr.com/pdf/N%20EMD%20GP35%20DIESEL%20LOCO.pdf

[GGNInNScale]

Hi to all   This is a really old GP35 when Kato made for Atlas (the blocky frames, 17728L/R)).  I have never experienced the "frame rot" that people are discussing- but I have lived in a dry climate area for the past 35 years.  As I mentioned, the plastic motor frame had sagged just a bit- put it on the table and it was slightly cockeyed.  Since it is a flexible plastic, there are no realistic ways to force it back (could have bought a new one from That Train Place, I guess).  The clearance on the "bottom" of the flywheel was reduced to near-zero.  I saw this as a black line on the flywheel.  So, I filed the frame slightly in the inside flywheel area, added a strip of Kapton under the end of the plastic frame (one end only).  This shifted the frame a few thousandths.  The frame spacers are dimensionally  fine (also make new ones with my resin printer if needed).  Then, isopropyl clean of all the moving parts, relubed with Labelle's, reassembled.  Tested on DC first to check for issues.  Now, the engine starts at low voltages and the current draw dropped as I mentioned.  Put in the decoder, put it on the programming track and checked the CVs, reduced CV2, 5 and 6 values significantly.  Runs great now.  I would post a video but Google and I do not see eye-to-eye.
Here is a picture.  The filing in the flywheel area does not show up well, sorry.  The top of the frame at the cab end was machined and filed to clear the 58923 Nano decoder.  The rear area was filed to allow the speaker and case to be mounted flat and clear the rear light. [ Guests cannot view attachments ]

[peteski]

OK, so now we have a reference point.
http://spookshow.net/loco/atlasgp3035.html



I don't own one of those, but I wonder if it would be possible to just rotate the motor cradle 180 degrees along the motor shaft axis, to have the sag turn into a lift?  Then the weight of the motor might have the motor centered correctly again.

[GGNInNScale]

Hi   Possible to rotate.  The motor carrier piece is "polarized" by a flat side and the round side where the motor clips into the plastic frame, and the frame is machined accordingly.

[peteski]

OK, so the cradle cannot be rotated. Any chance you could post a photo of the sagging end of the cradle (with the motor removed)?

[GGNInNScale]

Hi   I do not want to unsolder the leads from the motor, lights and the decoder, sorry.  Everything is fitted for final assembly wire lengths.

[u18b]

Yes, this is a start.  Thanks
Just worked on one last night.

Very key question.   The plastic motor saddle has a nub on top and bottom.    That nub MUST go on the end with the motor brushes.   In fact, it fits into a slot right behind the motor brash caps.

If it was installed backwards, then everything will be out of shape in the drive line.