"The only rare Marx engine is one that doesn't run" 
. Clean the commutator, wheels, axles and brushes, lube 'er up and I'll bet it takes right off. The center contact shoe, wheel surface where it contacts the rails, and the rails themselves need to be kept cleaner than for other makes, for Marx engines to run smoothly.
You'll have a lot of fun with it.
As mentioned by Stoshu the same-as-the-wheel-diameter gear causes the engine to rock 'n roll thru most switches outside of Marx. Exceptions are Lionel 1024 and 1121 switches, per other forum members' postings.
