This is an interesting set. I picked this up some years ago in order to finally get the B&O gondola with the black (or dark gray) interior. Upon close inspection I realized that the real prize here was the engine! The 401 unnumbered engine is one of those pieces that we all wonder why Marx produced. Under-detailed and without much pizzaz it's always been one of those pieces that I would rather not have. When I inspected this one though I was surprised to find that it was outfitted with the "mothers dread" airbulb, mechanical smoker.

I have found the airbulb smoke units in the past in 400 and 490 engines but never expected to find one in a 401. At first I thought someone had just swapped motors but the airbulb smoker requires a special smokestack. It's not something one could readily fake.

As you can see the smokestack is a larger diameter than usual.

Black Interior B&O Gondola

Here is the gondola that initiated my purchase of the set.

401 Puffer Engine

The airbulb puffer also utilizes a special motor unit.