I tried this. Lights came on but no sign of any movement of the armature. I had previously taken everything apart and oiled relevant parts. Not sure what is the next step.

Hi,
New here. I have a Lionel O set from the 40's from my Dad. It was probably new around 1946 and there's an old steam locomotive and a newer ('52-'53) diesel 624 engine that I'm working on. It's this one: http://postwarlionel.com/motive-power/diesels/nw2-switcher/624-chesapeake-ohio/

It was last used in 1974 when I was about 8. Then it was packed up. Now that my son is 6 I'm trying to get it going again after 40 years of inactivity.

I'm still using the original transformer which works (0-20 volts I think).

When I started, the locomotive wheels didn't turn and nothing happened when I put power.

Now I took it apart, cleaned and lubricated key areas and now the wheels spin by hand. I replaced the lights and they both work when power is applied.

The wheels are not turning at all when power is applied.

The lights turn on when the reverse lever is in one position. When the reverse lever is in the other position, the lights come on, there is a loud buzzing, but the wheels are not moving.

I have read many articles including this one: http://www.slsprr.net/technical/PopSci%20RefLibr%20No.15.pdf

but need some guidance on the next step.

I have tried manually moving the reversing drum mechanism while power is applied to be sure that it is not stuck in neutral, but that doesn't seem to improve things.

I'm not sure if power is getting to the armature. Would be interested to know how to test that.

What are the likely culprits at this point, or how can I find out what the likely culprit is based on what I've done so far and what might normally be done?

So I guess I'm trying to find out if it's a problem with the reversing mechanism (seems unlikely, as no position results in wheels turning in either direction weakly or otherwise) or an armature issue (more likely but trying to find out how to isolate this). I have medium electrical skills and I have a voltmeter but need to know what parts to use it on.

Would be great to get this going again....

I can add photos as necessary if that will help.

Thanks!