Issues rebuilding e-units (postwar)

You could possibly use an emery board, (the type used on finger nails), and rotate the drum with your fingers across the emery board.  In a sense, you are rotating the drum around with your fingers, and the coarseness of the emery board is taking off enough for the drum to work.  I hope you can understand the description of what to do.  If I am correct, there are different coarseness emery boards available.  It is time consuming, and tedious, but I think it is possibly a remedy to the problem.

TELEDOC is absolutely correct, emery boards and some patience does the trick, I know the white ones you talk about, and yes sometimes they tend to be a little too thick, I have used them in the past. In extreme cases, break out your trusty jewelers files and clean them up....I also trial fit the axle part of the drum into the e unit wall before I snap it all back together....I have a small round file too, if I feel like I'm close enough, a few passes with the round file in the e unit wall usually does the trick.....I know how frustrating it is....your not alone!

I've also had trouble with the repo ones in the past.  For that reason, I try to reuse or save every original one I can.  I also used to work at a hobby shop where the owner required the drum to be replaced on every engine I worked on when I serviced the E unit.  He would throw those old drums away, so I kept them and that pile has kept me supplied for the last 25 years.  Now the ones I really have issues with are the American Flyer ones, especially the late prewar ones.  Those suckers are a pain because they are actually two halves that are pressed onto the shaft that supports them in the E unit.  They have a tendency to change overall width and that causes some fit up issues...

AF for reference:

The other thing I noticed on some of the older reproduction lionel drums was that the copper fingers of the drum in some cases were slightly below the surface of the plastic.  I tracked several issues with hanging up and inconsistent finger to drum contact to that plastic being higher or not level with the copper fingers.  Once I filed or sanded the surface uniform, my problems went away.  That was a royal pain to figure out though.

you are so correct Dennis, I worked at a hobby shop too, we had to change every drum....those cheap white ones sometimes would drive me nuts!...ever had one that a thin veil of plastic would cover over a portion of the copper?.....but be so thin its transparent?

You  bet I did many times,   That's when I had to get out the file or sand paper!  hard to detect until you put it together and it does not work right

I have bought replacement drums from Rich Sappelli or Jeff Kane, no problems so far. FWIW. 

Thank you for the comments.
I posted about this problem for two reasons:

1 - I was looking for suggestions on trimming that hub without damaging the little post that goes in the hole

2 - I wanted to warn people who have not seen this problem before. It isn't much fun to rebuild an e-unit, only to discover that the drum won't rotate.

As far as the white drums go:
The oldest ones I purchased were very well made. I don't recall running into any that were miscast. The problems started showing up in later runs: issues with flash covering the metal contacts, crooked metal contacts, and now a drum that was too wide.  (maybe the dies were wearing out)

I wish I knew where I got the grey-green ones.

I haven't purchased any drums in years.

Another problem E-unit part I've run across was a two-finger contact that was mounted to a strip that was too thick. It would not fit into the slot until I shaved down the ends. (I didn't want to modify the e-unit itself). I've only run into that once. There are probably a few more in my stash, I never purchased e-unit components one at a time.