How to disassemble and service a Marx 333 locomotive

Last Updated on June 2, 2019 by Dave Farquhar

The Marx 333 was Marx’s biggest, fanciest, and most expensive steam locomotive during the postwar era. It shares some parts commonality with other Marx engines but if you’ve never worked on one before, it can be a little unclear how to disassemble and service one.

The main thing to keep in mind with a Marx 333 as opposed to other Marx diecast locomotives is the linkages. After you remove the screws from the front, you have to remove the linkage or the siderods, depending on the vintage. After that, the motor drops out easily. Servicing the plastic-bodied Marx 1829 is essentially the same.

Dropping out the motor

Marx made the 333 locomotive from 1948-1952 and 1952-1958, and it seems like they changed something or other about it just about every year. The siderods are the most perplexing thing. On mine, there’s a tiny slotted screw that connects the siderods to the linkage. Removing that frees the motor after I remove the two screws in the front. On other 333s, the siderods connect to the wheels with hex-head screws and you have to remove those screws and lift off the siderods from the wheels to free the motor.

Once the motor is free, you’ll see the wire from the headlight connected to a clip on the front. Press on the clip to release the wire.

Cleaning the motor

Some people spray down the motor with cleaner but I don’t recommend that. You can do a better job by removing the brushplate, and that lets you fix problems that spritzing down the motor with solvents doesn’t fix.

The Marx 333’s brushplate looks a little different from other Marx motors but the concept is the same.

There are two hex-head screws on opposite sides of the brushplate. Remove those, then be sure to keep track of the brushes. Sometimes they go flying. Sometimes they stick for dear life to the brush wells, and sometimes they stick to the commutator. Try to keep track of which brush was in which well and which way they were oriented if you can. The motor will run better if you put them back in the same way they were.

Cleaning the commutator

To clean the commutator, use cotton swabs with contact cleaner or alcohol to clean off as much of the grime as you can. Carbon dust from the brushes is conductive, but dirt isn’t. Oil usually isn’t conductive either, at least not in the quantities I find in these old motors.

Use a wooden toothpick to scrape out anything and everything in between the commutator segments. Carbon dust buildup in those gaps will cause the motor to lose power and eventually stop working.

Some people will use a little bit of metal polish on the commutator to shine it up and remove whatever stubborn residue you couldn’t get with alcohol or contact cleaner. If you do this, be sure to follow up with alcohol or contact cleaner one more time to remove any residue from the polish.

When I’m done, I like to apply just one tiny drop of Pacer Rail-Zip to one of the commutator plates. This helps quiet the motor down a bit, enhances conductivity, and helps the motor stay cleaner just a little bit longer. This step is strictly optional because if you apply too much, it does way more harm than good.

Replacing the brushes

Putting the brushes back in can be tricky. My favorite way is to put the brushes in the well, with the groove facing the spring, then put a piece of painter’s tape over each brush well to hold the brush in place. Then I put the brushplate back on, screw it down very lightly, then tug on the tape. It comes out easier than it sounds like it would.

Lubricating the motor

I like Labelle 106 grease and Labelle 107 oil for lubricating trains. You can use household grease and oil from your local hardware store, but I haven’t found anything better than the Labelle products.

I apply a drop of oil to each axle where it meets the bearing, and on the bearings on both sides of the motor armature. I also put some grease on the gears. The groove the front truck slides in also needs some attention sometimes. On mine, some old lubricant had gummed up and it didn’t move very freely. I cleaned off the old lubricant with a cotton swab and put a little bit of grease on either side of the groove. This helped the truck move much more freely.

You also need to lubricate the siderods and linkage. At any point where a piece can pivot, add a drop of oil. Just a drop. This helps the engine to operate as smoothly as possible. The more freely the siderods move, the more power the locomotive has for pulling cars.

Servicing the reverse unit

If your Marx 333 only runs in one direction, or doesn’t cycle consistently, or just sits there and hums, the reverse unit needs some attention. Don’t spray WD-40 into it like some people say to do. That does more harm than good. Marx reverse units fail for one of three reasons: corrosion, dirt, or poor contact.

Fixing corrosion

To fix corrosion, pick up and shake the whole assembly back and forth a good 100 times. This is usually enough to abrade off mild corrosion and make the train work again. I know it sounds crazy, but this works about 1/3 of the time. This is why I get frustrated with people who say Marx reverse units are hard to fix. Frequently it isn’t.

Put the motor assembly on the track and try it out before moving to the next step. If it works, put the train back together and enjoy.

Fixing dirt

To fix dirt, spray a little contact cleaner into the reverse unit. I use CRC QD Electronic Cleaner or CRC QD Contact Cleaner. I can’t tell the difference between the two and have no idea why Home Depot carries both.

Just squirt a little up into the reverse unit, then set the motor down on its wheels and let it run out. Give it about 30 minutes to evaporate, then try it out. The reverse unit responds well to this treatment more than 1/3 of the time.

Overhauling the reverse unit

If neither of these things work, the reverse unit needs an overhaul. Here’s the process for rebuilding a Marx reverse unit. Expect it to take an hour, or a bit less if you’re mechanically inclined. I am not mechanically inclined but now that I’ve fixed several, I can fix them in 15 minutes once I get the hang of it again.

There are people who will tell you it’s difficult. It’s not the easiest repair, but neither is it impossible.

Replacing the motor

I found the motor harder to put back in than it was to take out. First, reattach the headlight wire to the clip. Next, there’s a slot on the back of the motor that matches with an indentation on the cab. Line that up, then pivot the front of the motor toward the steam chest. You’ll probably have to slide the assembly forward very slightly to get the front to line up. With a bit of finesse, you’ll get it into place.

Cleaning the wheels

Hating on the Marx reverse unit is extremely popular right now for some reason, but I see far more problems with dirty wheels than anything else. Dirty wheels cause the train to arc a lot as it runs, and in extreme cases, not run at all. Clean the wheels with a cotton swab dipped in contact cleaner or mineral spirits. They clean more thoroughly than alcohol. Then, to prevent future arcing, I like to treat the wheels. Apply a tiny bit of No-Ox ID A Special, let it sit for 24 hours, then clean off the grease carrier with more contact cleaner.

After treating the wheels, it may be decades before they need to be cleaned again. Seriously. I use No-Ox ID A Special on my track too.

Changing the light bulb

There are two black screws near the front of the engine that hold the front in place. Remove those screws and the front comes off. Then you can access the light bulb. If your 333 light doesn’t light, try tightening the bulb before replacing it. Also make sure the wire from the bulb socket is attached to the clip on the motor assembly. These bulbs rarely run at full rated voltage so they rarely burn out. I see problematic or disconnected bulb sockets far more often than I see burned-out bulbs.

When I do have to replace the bulb, I use a 1449 14-volt bulb. For longer life, you can use a 1447 18-volt bulb.

To fix a bad socket, spray a little contact cleaner into the socket, then scrub it with a cotton swab. When that isn’t enough, applying a drop of Rail-Zip onto the tip of a bulb and another drop on the threads, then screwing in the bulb and waiting about 8 hours almost always brings the socket back to life.