1681 Lionel Jr remotor possibilities?

Throw a string of cars behind it...that'll slow it down. It looks like it's in relatively decent shape...would be a shame to gut it, especially after everything it's been through. 

Or put some weight in a car or two.

When the original motor still worked, I glued lead weights in it, pulled more cars, and that helped, but the motor got too hot, especially at lower speeds.  Right now, the engine is exactly how it was new, but most of the motor is a replacement I bought on Ebay many years ago.  I hesitate to make modifications because it has sentimental value, but I was considering putting together a separate modified drive unit that could be swapped in (or back out) without modifying the engine body.  I am not planning on modifying the current motor.  Another option is to remove the intermediate gear and have a powered freight car to run the train.  I very well may end up doing nothing, but it would be great if I could run it on the same loop as my DCS engines.  I have grades, so it takes a lot of attention to operate in original configuration, even with just one train on the loop.  Too bad it doesn't have the double reduction gears!  The only reason it is in decent shape is the restoration I performed many years ago.  There was a lot of rust and very little paint! The front pilot wheels are replacements, but all the shiny bits are original.  Here is what it looked like after removing the paint.  This was part of a set offered in 1934.  I still have the caboose, the lithography is pretty bad on one side, but I still use it.  The other train car with the engine was an 831 flat car bought as an add on to the set.   It was bought at Bragassa toy store in Lynchburg Va. The Bragassa family operated the toy store for a little over 100 years! The building is still there and looks a little better than the attached picture.  My Dad told me that they had trains operating in the window area at Christmas. 

Well, you did a brilliant job refurbishing it. 

I'm wondering if there's enough room for a small can motor in the loco, and if so, will it have enough zip to move it. Might require a worm-gear configuration with the can in the cab.

I have a prewar 1684 that tends to run hot after 10-15 minutes of run-time. Lubrication seems to provide some relief, but not much. 

PD

There probably is enough room for a can motor, or a small motor/gearbox combination.  If I do try putting together another drive unit, I would use some Lionel jr motor side frames and wheels as the starting point so the engine body wouldn't need modifications.  I am still wondering if the Lionel Junction little steam drive unit could be modified to fit the 1681 shell.   Below is a picture of a small motor/gearbox that is small enough to fit and could drive a set of wheels directly from the output shaft.  It is 3 to 6v, 48 to 96 rpm.  That speed should be just about right.

Why not just repair the original motor? It can be repaired to run smooth. The best transformer for your engine is a small one, like the original one. These have a lower start voltage and gives you some lower speed control.

The current motor in the engine runs fine for a Lionel jr and is exactly the same as the one that came in it.  It runs relatively smoothly, just not at speeds compatible with my other engines.  I probably should add weights if nothing else.  I have a small station transformer exactly like the one that came with the set.  It is ok until I try to pull more than three really light cars.  I have a few other small Lionel transformers that would probably work well - thanks for the suggestion.  If I add weight and get success with the small transformer, I could add a double pole switch to swap the loop from DCS to the small transformer.  There is still the problem of "lugging" the motor at reasonable speeds due to gearing.

Within about 3-4 years somebody had posted on using a can/pancake to repower a 2037 or other Prairie/Adriatic (I'm recalling a 6 driver unit, but just maybe a 4 driver. The short fat can fit in the frame, he pressed a gear on and maybe had made a mount plate or drilled for the can motor mounts; I forget.

Lost a little torque but was easier to manage if I remember right.

I'd search with "pancake motor" " repower" re-motor" and "2037" a few other small 6 driver numbers.

While it isn't a tin era post (it was post war), I think the motor # would work. I had it saved but it's in the memory of a dead phone. (If you find it, I'd love a heads up reminder of who & when they did it.

I read that post, and found it interesting.  I don't think it would work for the Lionel jr motor since it does not have double reduction gears.  I liked the fact that the motor in that post was just about the same size as the original armature.  The biggest problem with the original Lionel jr motor is the high gearing - too fast and not much torque.