MTH O Gauge Diesel - wheel came off axle

It depends on how much access you have to the offending axle- you could try knurling or upsetting the end with sharp diagonal cutters.  An easier solution would be Loctite retaining compound.  If you use it, make sure you keep it out of the bearing.  I guarantee that wheel will never, ever come off.  Krazy glue / CA might be a similar but less-permanent solution.

It sounds to me like somehow that axle escaped the knurling process during manufacture.  If it were my loco, I would be on the phone to Marge tomorrow ordering a new power truck.  Do they still require you to send the old one in?  Heaven forbid that someone might try to counterfeit a toy train! 

That happened to my MTH SW1 two years ago.  The axle had been knurled at the factory, but apparently not good enough.  I clamped needle nose vice grips on the axle and rotated them away from the engine. Rotated the axle 90 degrees and repeated. I pressed the wheel back on the axle using a C clamp.  I placed dimes in the wheel recesses to keep the C clamp from marring the wheel surface and to prevent pressing the wheel too far on the axle. I don’t run the SW1 every day, but I haven’t had a problem since.

 Loctite 380 BlackMax was recommended to me at the time, but since my makeshift knurling process worked, I didn’t use adhesive.  If you do go with adhesive, make sure to check the wheel gauge before letting the adhesive dry.

Thanks for all of the hints. I was able to reattach the wheel to the axle. Here is a photo of the wheel and axle. There was some knurling on the axle but not enough to grab.

I got some Loctite (the removable kind, in case I messed up). I used a large pair of channel locks to rough up the axle.

A close up of the axle after applying the pliers and a few drops of Loctite.

Here is the wheel reattached. It's on solid.

If it comes off again, use the Red thread locker, after all, you don't want it coming off!

If it ever comes off again use a retaining compound instead of a thread locker. I’m pretty sure retaining compounds will fill a .020 gap. 

Glad you got it done Mark. Stay in touch if you need anything. I appreciate all your help.

romiller49 posted:

If it ever comes off again use a retaining compound instead of a thread locker. I’m pretty sure retaining compounds will fill a .020 gap. 

You do have to use the right retaining compound, some are for tight fitting parts, others have some gap filling capability.  I use Loctite 660 that is for worn parts, and it does have gap filling properties.