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Marx 999 repair and service

I had a Marx 999 that didn’t run well when I pulled it out of storage. When pushing it along the track a few times didn’t yield any measurable improvement, I decided I’d better take it apart and give it a thorough cleaning.

In this case, I worked on a Marx 999, but everything I did applies to any other O gauge train Marx made except for the very late 490 locomotives, whose motors don’t seem to have been designed to let you do any more than replace the brushes.

Marx 999 repair and service: Do no harm

Please note: There is a lot of advice online that suggests spritzing down a Marx motor with WD-40 and/or TV tuner cleaner or contact cleaner. I’ve learned the hard way that you can damage it by doing this. You can do a much better, and safer job by partially disassembling it and cleaning it with cotton swabs.

Veteran Marx collector Al Osterud says the problem with using contact cleaner to clean the whole motor is that the wheel bearings were impregnated with oil at the factory. So dipping the motor in solvent can cause these bearings to wear out quickly.

Left alone, the bearings can survive about a quarter million trips around a 4×8 layout. I’m not exaggerating, that’s what they were designed to do. And replacing the bearings is labor intensive and requires special tools. It’s really best not to disturb them, especially when you’re working on a locomotive that’s worth $20. Frankly, with today’s lubricants I think a Marx train has more than a quarter-million trips around the track in it.

What I used

I already told you I didn’t use WD-40, but let me tell you what I did use, since if you’re reading this, you’re probably interested in doing what I did.

First, drop the motor out of the locomotive. I’ve covered that in detail before, so I won’t repeat it here.

Some terminology

Some people have been tearing motors apart their whole lives, and some people know nothing about motors except that trains have one. I’ll define terms at the end of this post if some of the vocabulary is a bit foreign to you. I remember someone telling me in my late 20s to clean the commutator, and I said, “What’s a commutator?” They said it was on the armature, and I said, “Great. What’s an armature.” So I get it.

Disassembling the Marx motor

Pull the brush springs out of the brush wells with a pair of tweezers and slide them over to the side. Do this for both brush wells.

Pull the brush springs out of the brush wells with a pair of tweezers and slide them over to the side. My tweezers are on one of the brush springs in this picture. The brush well is the circular brass piece that my tweezers are barely touching.

Once you have the motor out, it’s time to disassemble it.

You can make life a bit easier on yourself if you pull the brush springs out of the way at this point, before disassembling any further.

Use a pair of tweezers to pull the tip of the brass or copper springs out of the brass brush wells in the middle of the motor. Just pull the tip up and push it over to the side of the brush well. Doing this now makes replacing the brushes at the end much easier, because you won’t have to fight gravity. Gravity always wins.

You won’t need to drop out the brushes just yet. But this prep work makes reassembly easier. It also lessens the chances of the brushes going flying on you. You don’t want that.

Removing the brushplate

Marx 999 repair and service

Remove the two nuts at the top and the screw at the very bottom. Sometimes the brush plate lifts off easily and sometimes you have to gently pry it off. Work slowly and pry a little on each side, working your way around, if it feels stuck.

Next, remove the two nuts with a nutdriver. I needed a quarter-inch one, but it may be a different size in some cases. Next, I removed the screw at the bottom of the motor between the two wheels. At this point the brushplate should come free.

Mine didn’t lift up easily, so I had to pry it up gently, starting at one corner and working my way around. Don’t force it. Take your time.

Once it was free of the threaded posts up at the top, I lifted the brushplate up until it bumped up against the siderod. Then I pushed it forward, away from the wheels. At this point the graphite brushes usually pop out of the brush wells, but these stuck in there.

You’ll want to set the brushes aside at this point, paying attention to which one went on the top and which was on the bottom. If you put them back in the same way, the motor will run better.

Cleaning the commutator

Marx 999 repair and service

This isn’t the dirtiest commutator I’ve seen, but it’s contributing to why this engine doesn’t run as well as it could.

Next, I scrubbed down the copper commutator with cotton swabs and a solvent. Contact cleaner, mineral spirits, or naptha, applied with a cotton swab, will clean much more thoroughly than alcohol. Be sure to have plenty of ventilation if you use a solvent stronger than alcohol, and it’s not a bad idea to wear a ventilator while you use it.

Usually that isn’t enough, and in this case it wasn’t.

The best next step is to use a pencil eraser, which does a fantastic job of removing graphite from copper. Once the grime was mostly gone, I stopped.

I followed the eraser with some metal polish, then followed the metal polish with one more round of solvent on a cotton swab to clean away as much of the residue and remaining dirt as I could.

Marx 999 repair and service

Clean the commutator with a cotton swab and some mineral spirits or even alcohol. This may be the most essential part of Marx 999 repair and service.

While cleaning, I paid special attention to the grooves in between the commutator plates. Buildup there contributes to a poor running motor more than anything. In the picture on the right, I’m cleaning the groove with alcohol and a cotton swab. It also helps to gently scrape the grooves with a toothpick. I alternated between the toothpick and a cotton swab until I was sure the grooves were clean.

Alcohol is a safe choice to clean the slots since we don’t necessarily always know what material was in the armature. Alcohol is a safer choice than harsher solvents. It won’t damage the insulation on the wires.

Some people just wipe the commutator down with alcohol, clean the grooves, and stop right there, but I like to get it as clean as I can. The cleaner it is, the longer the motor will run well, and the better it will run. I’d rather run my trains than clean them, so I think it’s worth spending an extra five minutes to shine up the commutator. Some people get aggressive with Scotch-Brite pads but I don’t recommend that, because messing up the commutator becomes an expensive repair.

Cleaning the brush wells

After cleaning the commutator, I also cleaned out the brush wells with a cotton swab. This isn't always necessary but it never hurts.

I cleaned out the brush wells with a cotton swab. Also note how much cleaner the commutator looks at this point.

I also cleaned the brush wells. This isn’t always necessary, but when you have the motor apart anyway, you might as well go ahead and do it, since it never does any harm. You can remove some oxidation from the inside by cleaning it with a bit of metal polish, then following it up with solvent.

If you’re not in a hurry and you’re willing to let the motor sit overnight, work a little bit of Rail-Zip into the brush wells and onto the brush springs, let it sit overnight, then clean them with solvent.

The Rail-Zip can loosen dirt that’s stuck in there and also works chemically to remove oxidation. It’s not a very good conductor, but if you give it a few hours to treat metal, it makes old metal into a better condutor, so the motor will run cooler and have more power.

Giving the commutator a health check

While you have the motor apart, measure the continuity between the plates with a multimeter. I didn’t have my good multimeter available so I couldn’t take pictures, but on a good motor you’ll see a resistance of a couple of ohms between any two of the plates, and the resistance should be fairly consistent. You should also see infinite resistance between all of the plates and the axle.

If you see conductivity between the plates and the axle, you have a short. If the resistance is inconsistent, you probably have a short. A motor will never run well with a shorted armature, and replacing the armature is usually cheaper than repairing it. If the resistance is overly low, the commutator needs to be cleaned.

Reassembling the Marx 999 locomotive

At this point, everything was clean and in nice shape, so I put it back together. Before putting the brushplate back on, I spun the wheels, or perhaps I should say I tried to. The motor was locked up because something is misaligned. Sometimes just working the armature back and forth frees it back up, but usually I have to reach in with a popsicle stick and spin the armature with it to get it lined back up where it’s supposed to be.

I’m sure a lot of the seized-up Marx trains on Ebay were just disassembled once and someone couldn’t figure out how to get the armature freed back up.

Replacing the brushplate

Next, I fit the brushplate underneath the siderod, then lined it up with the posts and the armature. Once I got it into place, I pushed the brushes back into the brush wells with the little groove facing up toward me, then I used my tweezers to pick the brush springs back up and put them onto the brushes. Usually the groove doesn’t quite line up with the springs, so I gently rotate them with the screwdriver. At this point I also push the brushes down, since the springs don’t necessarily push the brushes all the way down to engage the commutator on their own right away. At least on this motor they didn’t.

If you get frustrated, take a break and come back to it. This is a hobby. It’s supposed to be fun–and it will be fun to watch that locomotive racing down the track better than new.


If the motor has a felt wick, apply a few drops of oil to it. This one was completely dry.

If the motor has a felt wick, apply a few drops of oil to it. This one was completely dry. It also helps to put a drop of oil on the part of the siderod that slides, just to the left of the large drive wheel on the left.

Once I had the motor back together, it was time to lubricate it. Lubrication is another mildly controversial point. Marx originally recommended Vaseline, but we have better lubricants than Vaseline available to us today. I put synthetic oil on the axles and synthetic grease on the gears, and this practice has served me well for 15 years. Then again, Al Osterud has been using Vaseline on his Marx trains for longer than I’ve been alive. But I do think modern lubricants can help trains run longer the same way modern lubricants help automobiles last longer than they used to.

I put a few drops of oil on the oil wick–Labelle 107 is one of many good oils available today–since this motor had one. Some motors just have a bearing. If that’s the case with yours, apply a couple of drops to the bearing.

Next, I flipped the motor upside down and squirt a drop or so of oil into the bronze bearings that the axles run through. It also helps to put a drop of oil on the siderods to help them glide more smoothly. Then I put another drop on the axle at the front of the train. Any wheel needs oil at the point where its axle rubs against anything. Some people put oil on the gears as well, but as fast as Marx motors run, they’ll just fling the oil onto the track. I put a generous helping of Labelle #106 grease on them instead. I just dab a bit all around the gears in the center, then spin the wheels a bit to spread it around evenly.

After a good cleaning and lube, my Marx 999 doesn’t run like a Swiss watch like my Lionel 675 does, but it does run at least as well as my old Timex did. And that’s a-ok.

But what if yours doesn’t? Sometimes you’ll do all this and all the engine does is sit there and buzz. In that case, not all is lost. The reverse unit needs a cleaning. Clean up that reverse unit, and then your engine will run better than new.


Armature — a big spinning triple electromagnet. The constantly changing poles cause it to spin, making the motor work

Commutator — the copper plates on the armature that cause the poles on the armature to change polarity

Brushes — graphite cylinders that engage the commutator to provide power to the electromagnets

Brush wells — the brass tubes that hold the brushes in place

Field coil — the wire windings at the top of the motor that create a magnet that attracts and repels the magnets on the armature

Bearing — cylinders, usually made of bronze, that hold an axle in place. Oiling them occasionally helps them to last longer

Siderod — the large rods that run between the rear drive wheels and the fake piston at the front of the motor

Drive wheels — the large wheels in the center of the motor

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