Help ! What’s this ????

Looks like zinc pest to me. Unfortunately, there's plenty of info here on the forum about it. Better check the boiler casting too.

I do t think all is lost yet. Was the shelf in a garage or basement where dampness and humidity could get to it? Take an old toothbrush and knock that crud off. Wipe the wheel clean with a rag with a little gun oil, or penetrating oil, and see what things look like....send a pic afterwards ( a close up) and we can then see if there’s any noticeable swelling that would indicate a failure of the metal.....it’s hard to see what’s going on with all the fuzz on it right now....I’d take the truck off to clean it...ain’t but 2 screws..........Pat

harmonyards posted:

I do t think all is lost yet. Was the shelf in a garage or basement where dampness and humidity could get to it? Take an old toothbrush and knock that crud off. Wipe the wheel clean with a rag with a little gun oil, or penetrating oil, and see what things look like....send a pic afterwards ( a close up) and we can then see if there’s any noticeable swelling that would indicate a failure of the metal.....it’s hard to see what’s going on with all the fuzz on it right now....I’d take the truck off to clean it...ain’t but 2 screws..........Pat

I agree. No need to replace the truck. "Zinc pest" does not usually look like this (in fact, often does not look like anything until the crumbling begins). 

Come to think of it, I have seen this sort of thing on perfectly sound Post War Lionel and other cast and plastic pieces. Essentially it wipes off. Wipe it down with some light oil after cleaning.

That’s not zinc pest. It looks like corrosion from direct contact with moisture.

Hard to get zinc pest on a wheel that is not zinc.

Not zinc pest... I would simply use my lubricant of choice and wipe it down.

What type of shelve was it sitting on?

Thanks to all for the replies / guidance. The trains were not in a damp basement but in a large bedroom with AC, heat, double pane windows, uv protection and displayed on glass shelves. Nothing environmentally harmful. 
Only the MTH Hiawatha front wheels suffer the weird malady out of dozens of engines. There must be some impurity unique to this run of wheels. 
It is now my last engine to pack for a move. I will clean off the “crud” before wrapping and boxing the engine but wait until after the move to wipe down with a light oil. 
Again - thanks for the comments / valuable guidance. 👍

TrainBub 🙂

TrainBub, there have been no reported problems in the wheel production of that Hudson. And the reaction is an external chemical reaction, not an alloy or metal composition problem. Somehow those wheels were exposed to a corrosive element. It could have happened at the factory or anywhere up until the point you discovered the problem.

So clean it up, then inspect the wheel for any pitting. If it is smooth, you’re set. If it has deteriorated, you’ll have to decide if it bad enough to warrant a replacement of the wheel set.