Here's the skinny on that engine of yours.
It is a Rivarossi 0-8-0, made starting about 1969.
Since the motor runs when you have it out of the frame, you have a really good shot at resurrecting the engine.
Those motors are notorious for overheating and melting, but if they are cared for and not over-oiled, they can hold up.
The first thing you have to do is fix up the driving wheels and get the rods on in correct alignment. This is called "quartering", and sometimes can be a very difficult task. Lucky for you, quarting on a Rivarossi steam loco is about the easiest there is, because of how it is designed.
1. Using a jewelers screwdriver, tweezers, and/or a very tiny pair of needlenose pliers, unscrew the the main crank screw on the 3rd driving wheel (driver) from the front. It is the only one with a screw. TAKE CLOSE-UP PHOTO before you remove the screw and be extremely careful not to lose the screw or any spacer washers under it. You need to put them all back in the same order.
2. Once you get that screw out, the rods will all come off. Notice at this point that the siderod (the one that goes flat alongside all 4 drivers) attaches to only the FRONT driver by slipping its fork-shaped end under a pin that is pressed into the driver. Just make a note of this in your head for later.
3. Flip engine on its back. It really helps if you have a block of foam with a groove cut out to hold the engine up (an engine "cradle" which you can buy from model railroad supply stores). If you don't have such a thing, you'll have to improvise. Try rolling up a couple of handkerchiefs or washcloths so you can place the two cloth rolls down with the engine lying between them.
4. There are two screws that hold a cover plate in place on the bottom of the engine. Remove the screws and plate. Be CAREFUL - there are 3 plastic U-shaped piece that slip into slots in the frame between each pair of driving wheels. If they partially lift out, put them back in.
5. Now, carefully lift/rotate, and then drop back in each driving axle until you get all 4 of them in so that
the holes in the outside wheel faces (the "crankpin holes") all line up at the bottom. They can line up anywhere you like as long as they are all in the same exact relative position of rotation, but it is easiest to see that they are lined up by getting them at the bottom. It can be a little tricky, because as you try to drop one back in, it will try to rotate the gear that it mates with and that can rotate the OTHER drivers, making them go out of line again. So when you drop one in, try to hold the other three still with a finger so they cannot turn.
5b. VERY IMPORTANT - Check that the 4 drivers are all placed in the frame with the "hot" driver on the correct
side. As you look at the wheels from the bottom, you will notice that for the two wheels on any axle, ONE wheel has a metal plate slid up against the back of it, but on the other side, you will just see the plastic spoked wheel center with not metal plate. With the engin on its back, and the rear of the engine to your LEFT, the 4 wheels with the metal plates up against their backs should all be NEAREST to you.
If they are not... pull the offending ones out, flip them around and put them back in.
You MUST get them all correct or they create a short circuit and the engine will not run. It is common
for "tinkerers" to mess around withthese, get one flipped around, and then never get it to run again and give up.
6. Once you get all 4 so that their crank holes line up, put the cover plate back on and put the 2 screws back in.
7. At this point, with no motor and no rods, you should be able to smoothly rotate all 4 wheels and they should turn in unison.
8. LAY THE ENGINE ON ITS SIDE.
Put the siderod back on, on one side. Remember that photo you took when you took out that screw? That's going to be important now. You need to put the siderod back on, with spacers, and the other rods that all connect over that one screw on the 3rd driver, just as they were originally. On that engine, I believe it goes:
- put spacer washer over the threaded tube that is inserted in the hole in the 3rd driver
- place siderod front fork under the pin on front driver
- drop the siderod hole over the threaded tube in the 3rd driver (right over the washer you already put there)
- drop the "main rod" (the one with a larger end on it with a hole in it) over the threaded tube
- now the tricky part, place the eccentric crank (this is the only remaining piece you haven't connected - it
is a thin, light rod with several joints in it, and the end has a small jointed piece that can rotate.) That last little
piece with the hole sits on TOP of the threaded tube, it doesn't go over it. You have to hold it there while you put the screw through it into the threaded tube, and then turn the screw in with a jewelers screwdriver.
And you have to do all this without losing the screw, or getting frustrated an uttering bad words.
9. When you get the screw most of the way in.... VERY IMPORTANT NOW.
rotate the wheels so that the crankhole (where the screw is) is at the BOTTOM of rotation.
Rotate that eccentric rod (the thing one, sitting on top of your stack of rods on the third driver)
so that the 3 pieces of the rod go straight up - straight over - straight up.
You need to hold it in that orientation while you tighten the screw.
Once the screw is tight, that eccentric rod will be held in that orientation and you should be able to rotate
the 4 wheels and watch that the rods work smoothly.
10. Now do the rods on the OTHER side. And then make sure all 4 wheels rotate and all the rods work.
11. The motor....
Ease the motor in from the back. As the worm gear engages the idler gear inside the frame,
you can just wiggle the driving wheels back and forth a little to engage the teeth and let the motor push all the way in.
12. Put the two screws into the back of the motor to hold it in place.
13. You should be able to wiggle the drivers now. Not turn them, but there should be some play in them.
If there isn't, you don't have the worm gear engaged properly so loosen the motor screws and try again.
14. Apply power to the motor using clip leads from a power pack on half speed (not 1/4 or 1/3 .. some of these old Rivarossi motors won't start turning until you get the power pack up about half way, especially if this thing
has been sitting around for years. Just connect the + and - leads to the silver contacts on the top and bottom of the motor. On the bottom, be sure to only touch the pin that protrudes all the way down . Do not let that lead touch the frame or other parts of the motor, which will create a short circuit.
15. Assuming that works... Look under the tender (the "coal car"). You will notice that for each axle, one wheel has a metal center (the "hot" wheel) and the other side is a plastic center. All 4 metal centers must be on the OPPOSITE side from where the metal plate "hot" wheels are on the engine. If any aren't, you need to carefully use a jewelers screwdriver to pry out the wheel axle, flip it around, and reinsert it. And note the metal wiper strip that goes over the screw in the center of the truck (there are two "trucks" with two axles in each one). Pay attention that that wiper and make sure the wheels and wiper go back in correctly.
16 Connect the engine to the tender by first looking at the flat metal strip that connects the two (the drawbar).
THere is a fine spring steel wire that should be positioned, and slightly bent, so that the end of it lies just to one side of the hole at the end of the drawbar. If it isn't, bend it over so it is. Now, insert the pin under the back of the engine (coming out of the bottom of the motor), into the hole in the end of the drawbar... MAKING SURE to bend the wire over... ACROSS The hole, and then insering the pin , so that the wire is sprung against the pin when it is inserted.
Holding this together, get it all on the track without letting the pin pull out.
This was a very very long dump... but good luck. I hope you can get it to run.