Prewar American Flyer 1121 2-4-0 Steam Engine O Gauge!

That is a whistle unit. It is in place of a reverse unit. The only way to get parts is to get another engine with working whistle unit. Hard to find. The red slide was to change pitch or shut off maybe. Anyway it has nothing to do with motor running. You can just leave it off. If it hums, it could be a number of things. Start simple, cracked insulation, dirty/stuck brushes, broken/weak brush springs, dirty commutator with clogged slots. I have worked on quite a few of these, and most of the time it is one of the above issues. Good luck.

Chris

So the engine runs forward only? No reverse unit?  Thanks for the advice, I will keep checking.

Yes, that's correct. I'm sure you'll be able to fix it yourself, unless it's a bad field or commutator. Commutators can sometimes fixed also, but check every thing simple first.

CAA: Thanks, got it running.  The brush plate rivet on the upper right side was loose, so I restaked it and it now runs!   Of course I have another question.  Is there supposed to be a smaller gear attached to the very small splined shaft of the whistle?  Note picture where the larger gear to the left should be 'running' another small gear for the whistle.  

Thanks for the help! This forum is just great!

So glad you got it running. Yes, small gear is missing. I looked for years for same, and finely gave up. Most likely you can only find it, and the impeller on another loco. All the ones I ever found were in better shape than the one I was trying to fix. You may get lucky on e-bay or a train show. Anyway looking is half the fun. Rods, wheels, brushes and springs can be found at Henning's or Port Lines Hobby, as well as a few other places.

Chris

  If all you have is the engine and you are wondering what goes with it - here's one set it pulled The Blue Streak - set #7550 from 1937

I wouldn't bother trying to fix the whistle.  That style of whistle is typically so faint that you cannot hear it over the sound of the engine running. 

Out of all of the engines I have with that style whistle, I only have one that I can hear when the engine is running.

NWL

Wow!  Great info and great picture, thanks so much.  Here is short video of it running, even after grease and oil lube it sure sounds rough but it is well worn.

Thanks again!  I will pass all this knowledge on to engine’s owner who picked this up at auction.  

Saw this post.   Wondering where to get from wheels

Henning's Trains or Port Lines Hobby.

Good luck,

Chris

It sounds like the wheels may be slightly out of quarter. Does it make the same noise when run without the rods?

I have the same engine. I think it is referred to as an XX or 401. Mine is a little better, but not much. I've oiled both ends of every turning shaft and moving part, cleaned commutator and groves, new brushes and springs, and it still has that dry bearing sound.