Lionel 520 Boxcab Armature

The Back-up Armature is on the right in the pictures.

According to Bob Hannon's "O Gauge Reference Manual", which is the most authoritative source I've seen on this subject, 1.4 ohms is the correct impedance for both the 2034 and 520 armatures.  (The part number 2034-131, is the same for both.)  2.5 ohms is way out of spec.  Parts for that motor are cheap and readily available; you can replace the armature without pulling the pinion gear.  If I were in your situation, I would get another backup armature and make sure that it ohms out to the correct spec.  My $.02.

The red wire one looks as if was rewound.

Ted, I'll take your advice and see if I can pick up another back-up armature. I bought this back-up armature at a train show for $5 after all the physical measurements were comparable to the original armature. I guess I'll have to take my multi-meter to the next train show.
Ted & Chuck: I have 2 more questions:
1) As mentioned before, I tried this Back-Up Armature in the BoxCab and everything ran fine, but I was concerned about the impedance difference and put the Original Armature back into the BoxCab.  If the Back-Up Armature was re-wound (with red wire), could this cause the difference in impedance from 1.4 to 2.5 ohms?
2) Would the difference in the ohm readings (1.4 vs 2.5 ohms) have any detrimental effect on the Boxcab  with prolonged use of this Back-Up Armature?

Thank you in advance.

I would think the red wire armature will overheat after a period of time. Another red flag is if you look at the center picture looking down, look closely and you will notice the red wire one the commutator top is in a different position with relationship to the pole lamination stack. Compare to the original on the left. It is not timed correctly and will also cause overheating. It's hard to tell from pictures but it looks like there are more windings than needed on the red wire version. Install it and run for 20 minutes and see if it gets excessively hot. Or if you have a Z4000 or a ZW with meters, put the engine together and add a 6 car train and compare amperage draw.  As Ted stated, 2034 armatures are a dime a dozen, probably the most common postwar armature out there.

Unfortunately, I don't have a ZW with meters. But I can do the following experiment:
I'll run the Boxcab with both the original and back-up armatures for 20 minutes each, looking for
any noticeable operational or temperature differences. Then I'll post the results.

Sharp eyes Chuck, I agree with your assessment.  With a higher resistance I would expect it to run hot.  The shifted timing might also make it reluctant to start.

@Anich if you don't mind, I would like to know how fast the loco runs with each armature for a given track voltage.  For example: at 8 volts, 10 volts, 12 volts, etc.  Also, what about starting and pulling characteristics?  Will it start readily when coupled to a train?  Or does it sit there and hum until you give it a little push?  Can't wait to hear your results!

Yea the commutator on the right is not in the right position.This usually will result in not starting running right away sometimes you have to push it. I thought Bob called it out of phase. Also if it was rewound with extra turns ohms will be higher.

Results of the experiment:
WITH THE ORIGINAL ARMATURE: The Boxcab by itself ran well at 10 volts. When 6 cars were added, it ran flawlessly at 12 volts for the entire 20 minute run (good starting and pulling characteristics). After 20 minutes of run time, the brush holder and the armature were very warm, but certainly not hot.

WITH THE BACK-UP ARMATURE: The Boxcab by itself ran fair at 12 volts (after pushing it to get started). But when 6 cars were added, it was very sluggish -  it just sat there and hummed until I gave it a push (poor starting and pulling characteristics). Even at 14-16 volts, it would slow down and stop.

Therefore, this Back-Up Armature is not a suitable replacement for the original. All of your assessments were spot on. I'll get another back-up armature that meets both the physical requirements and exhibits the correct impedance of 1.4 ohms (I'll take my multi-meter along to the next train show).

I provided better pictures to view the misalignment of the back-up armature (as Chuck previously stated: the back-up commutator top is in a different position with relationship to the pole lamination stack when compared to that of the original). The Back-up Armature is on the right in the pictures. Picture 2 is a side view of the armatures (showing the misalignment) when the armatures shown in Picture 1 were turned on their side.

Ted, Chuck and Jim: Thanks for all of your comments which provided a thorough conclusion to this issue.