# Marx 21 Diesel (with more Marx reverse unit info)



## T-Man (May 16, 2008)

I decided to clean this up and get it running. After many years in storage the reverse unit cycled but it would not run. SO here is my story. In case anyone wants to know how to clean out the revese unit.

The shell.










The motor.










The motor has a large top and is attached to a plate to rotate.










The plate.










The recess


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## T-Man (May 16, 2008)

*Clean the armature.*

Two screws hold the truck sides and must be removed.










REmove wo nuts and a screw to get at the armature.










AHA dirty just as I thought.


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## jwse30 (Jun 30, 2012)

What a timely topic for me. I've got a set of 21s that I refitted a 1095 motor into the powered unit (it has a double reduction motor so it can go through modern switches), but the motor is incredibly weak. Haven't gotten around to trying to figure out why. Hopefully your results will get me motivated.

Thanks,

J White


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## sjm9911 (Dec 20, 2012)

Tman, cool looking engine. And great pics as always. I always learn a lot from your posts . Keep um coming. Thanksn


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## T-Man (May 16, 2008)

Power loss is a sign of weak springs. New brushes will help, after all they are longer and not worn. Thanks for the comments,

Next, the revesre unit removal. I used a tack puller to spread the frame. The rear nubs kept reseating on the frame from working side to side so I used a paper clip in the hole and later a small srewdriver.










Point of no return now.










The reverse unit was pulled out. I disconnected the wire from the center rail contact shoe for more clearance. Shown is what I call the cradle. It rocks back and forth. Three contacts from move between two fingers. Power goes to one and the other goes to the first brush of the motor. Two outer contacts are connected to the motor field and the other is the opposite end of the field wire. This is how the current is reversed in the field to change motor direction.










I removed the coil and the plunger. I also removed the isoslated plate for the coil connections.










I polished up the wire and plunger with scotchbrite. Of course straightened out the bent parts after removal.
Anything bent will have to be straightened out.Getiing it back together is not my favorite part.










Of course I removed the reverse unit coil It was rusted so I cleaned it and used gun blue on it.










One side of the wire broke so I added on another piece. The enamel needs to cleaned off before soldering this wire. I use an Xacto knife and scrape the wire on a flat surface until I see it shine.











Test the motor.

The thick black wires are the field coil connections. One jumper goes there the other attaches to the wire to the motor. Touch a power conection to the other firld wire and ground the frame. The motor should run . It did.


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## T-Man (May 16, 2008)

*Clean the reverse unit.*

Here I cleaned the contacts on the cradle and the fingers. I cut a small strip of 220 sand paper and inserted it between the finger and contact. WIh pressure from a small screwdriver I pulled the paper out. I repeated this until clean. Each finger was done and the three contacts had to be positioned to be cleaned. FUn huh! I bet you can't wait to do this. A few passes for each side did the trick. I did not double up on the papper. One side at a time.










One finger needed adjustment. I used a paper clip with a bend. Pulled up next to the rivet and pressed down on the end with a small screwdriver. This got my connection back.

Time to test the motor and make sure the connections are good. The wire from the center contact is shown to the right. My transformer connections are on the frame and the power finger. Rock the cradle from the side to get a motor response. Make sure both directions work.










Motor works, reverse unit connections are good.

I picked up the motor to run it. The posts sqeeked on the gears so I used lithium grease on them. A little oil all the way around. WIped off the excess too.


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## sjm9911 (Dec 20, 2012)

Nice work t -man. I use white lithium grease there also. ( glad to know it wasn't wrong ).


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## tjcruiser (Jan 10, 2010)

Very nice inside-the-hood pics and descriptions, T-Man. Most helpful ...

G'john sent me a Marx reverse unit some weeks back, and I've been curious to see hot it works. I've opened it up, and followed your descriptions in this (and your other) threads. I haven't hooked mine up to anything yet, but I'll try that at some point.

Cheers,

TJ


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## T-Man (May 16, 2008)

*slots and lots.*

I wanted to show that is was not simple and to give the detail it deserves.
The engine was running today, and the fat wheel gear and wide center bar don't like switches or uncoupling tracks. It was a half circle run.

TJ have fun, when you get to it.


Next, I added the coil to the cradle assembly. Lining up slots to do it. Also, I have the pawl wire face the same side as the insulated board.










Then I gooped the small wires to the coils. These see stress with movement so I used gasket cement.










I installed the insulated board, twist tabs and soldered the coil back in place.
One to the frame, the other to the positive terminal.










Then I slipped the revesre unit in and squeezed the ends. To get the end tabs fit in the slot, a twist of the front side as as shown may be needed.











The truck sides are next. Showing the required spacing,





















On the track test the drawbar dragged and sparked. I ended up compressing the rivet more.










Final inspection ans pass.:thumbsup:



















Twelve inches long TJ, a beast by Marx standards.


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## tjcruiser (Jan 10, 2010)

That is quite big, huh?!?

Nice rebuild. The reverse unit pics / descriptions are great info to have here.

Was that originally a screw/sleeve/nut on the truck, or was it a rivet rod? If the latter, your brass sleeve assembly is a perfect / easy redo.

Cheers,

TJ


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## T-Man (May 16, 2008)

TJ, is was a brass sleeve. One popped out and I have been looking for it since.

It runs nice. The weight helps. It is wedged between the motor frame plates.


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