How to disassemble a Marx 666 locomotive

Disassembling a postwar Marx 666 locomotive, or its plastic counterpart the 1666, isn’t too difficult, but it helps to have some instructions.

Marx designed its trains so that a father or older brother could service them, so it comes apart with simple household tools, and you can get most of what you’ll need to service it at the nearest hardware or auto parts store, with the exception of the bulb for the headlight.

What you’ll need

Projects like this always go more quickly when you have what you need in advance.

Get replacement screws that match the screws already on your locomotive. Marx usually would have used slotted screws, but I find Phillips screws on them from time to time. If you’re concerned about ease of maintenance, Phillips screws are easier to work with.

Replacing the Marx 666 headlight

Marx 666 front removal
The front is ready to come off in this picture. Note the missing screw to the upper left. Removing it and its counterpart on the other side are all it takes to slide the front off.

You’ll have to do this step even if the headlight works and you aren’t replacing it.

Remove the two screws on either side of the locomotive front. If you just need to change the headlight, you can just remove the front. You don’t have to drop out the motor. With the two screws removed, the front slides out. And then, with the front removed, the light bulb just screws out.

Marx 666 front removed
Here is the Marx 666 with the front removed. Note the bulb to the left.

The bulb is a standard 14-volt 1449 type commonly used by Lionel, sold by Trainz.

A 14-volt bulb is a bit under spec though. A Marx transformer can output up to 15 volts, which will burn out a 14-volt bulb prematurely. An 18-volt 1447 will also work and will last longer. It will just burn a bit more dimly, but the increased life expectancy is worth it. Since changing the bulb is a bit of a pain, I would replace it with a 1447, ideally an LED version. Either type will likely last a lifetime, but the LED bulb will reduce the load on your transformer by a good two watts, so it’s an upgrade worth doing. You might want to buy several and upgrade your whole fleet, or at least your most commonly used locomotives.

The procedure to replace the front after changing the bulb is described a few paragraphs below.

Dropping out the Marx 666 motor

Marx 666 motor removal
The motor tilts out when the front is out and the screws are removed.

If you need to drop out the motor, remove the headlight first. Next, remove the two screws on either side of the motor, in front of the two large driver wheels and siderods. Do not disturb the exposed screw on the motor itself, in between the two screws. It doesn’t need to be removed for disassembly, and if you lose it, the motor won’t run without it. One of the most common reasons for Marx motors not running is because that screw is missing, so if yours won’t run and that screw is missing, you may be able to just stop here, replace that screw, put the locomotive back together, and have a running train again. Sometimes that screw is a 6-32 machine screw and sometimes it’s a 4-40 machine screw. To figure out which one you have, try one of the screws from the side of the locomotive. Don’t force it in. If it threads in easily, you need a 6-32. If it gives resistance, you need a 4-40. Any well-stocked hardware store will have both kinds; get the shortest screw they have. A quarter-inch screw is plenty.

Assuming the problem isn’t a missing screw in the motor, here’s how to continue with the disassembly. Tilt the motor assembly down, then alternate between pulling it down and forward until it releases. Be careful not to lose the top piece of the smokestack.

Service the motor as needed. I have some advice on cleaning and lubricating Marx motors here if you need it. If you service the motor, be sure to test it before reassembling the locomotive to avoid having to turn it around and disassemble it again.

Let’s talk lubricants for a minute. Lucas Red n’ Tacky grease works splendidly and is available near you. While you’re there, pick up a quart of synthetic 10W-30. Apply grease to the gears with a toothpick, then apply a drop of oil to the wheels where the axles meet the bearings with another toothpick. Use the leftover oil in your lawnmower come spring.

Something else you’ll want to do while you have the motor out is to clean the driver wheels. They are always filthy, even if they look clean, and will run much better after a cleaning. A cotton swab with some mineral spirits is the cheapest way to clean the gunk off them. Mineral spirits, if you’re not familiar with it, is a cheap and effective solvent sold in hardware and home-improvement stores in the paint aisle. It’s normally sold as a paint thinner.

It would also be a good idea to blow the motor out with some compressed air. You can get by without this step, but it can loosen some of the debris that’s accumulated through the ages and make it easier to get it clean.

If you lose one or both of the screws holding the motor in, they are 6-32 machine screws. Replacements are available at any well-stocked hardware store. Get the shortest screws they have to avoid interfering with the operation of the side rods.

Replacing the motor

Unless you have the steady hand of a brain surgeon, the top of the smokestack came out when you pulled the motor out of the body. This part has a groove in it to help you replace it properly. Place it in the top of the stack, then turn it until the groove engages. At that point it will drop down into place.

To reassemble, tilt the motor in first. There are grooves in the motor assembly that engage the back of the locomotive. It takes a bit of trial and error to get everything to line up as the inside of the locomotive is a bit cramped. Work the motor assembly forward and backward until it fits properly. Once you tilt the motor’s grooves in, sometimes it helps to look at the locomotive from the front to make sure everything is lining up. Pay special attention to the top of the smokestack. It’s a separate part so that it will have some play, but if it pops out or isn’t aligned correctly, the motor won’t go in properly.

You can tell the whole assembly is lined up when the screw holes in the front are all lined up and the motor doesn’t fall out the back. Replace the two screws that hold the motor in place.

Replacing the front

The wire goes into the hole in the copper plate right next to my thumb.
The wire goes into the hole in the copper plate right next to my thumb. Note how I’m pushing the thin black wiper out of the way with a screwdriver.

Before attempting to replace the front, examine the wire that comes from the light bulb. If the stripped end is frayed, twist the ends back together so they form a tight unit, then straighten the end. It will make replacing it much easier.

The wire for the light bulb engages a hole in a copper plate in the motor that’s visible from the front of the train. Push the wiper out of the way with a screwdriver to expose the hole. Patiently push the wire into the hole, then once the stripped portion of the wire is in, pull the screwdriver out to release the wiper, which will hold the wire in place. With some practice it might be possible to do this maneuver with two hands, but I find it easiest to hold the locomotive between my legs, hold the screwdriver with my non-dominant hand, and use my dominant hand to guide the wire into place. You might find it easier to guide the wire in with a pair of tweezers.

It’s not the easiest to put back, but I have to admit it’s a clever design and it didn’t add much to the cost of the locomotive. With any luck it’s something you’ll only have to do every couple of decades.

With the wire back in place, orient the front of the locomotive correctly, then replace the two screws that hold it in place. If you lose either of the screws for the locomotive front, they are 4-40 machine screws. Most hardware stores will have screws that will fit, but it will probably take some luck to find a store that has blackened 4-40 screws in stock. You may have to buy a brass or steel screw and paint the head flat black.

And that’s all there is to it. Once the Marx 666 is serviced with modern synthetic lubricants and has a modern LED bulb in place, it can likely run for decades before needing major maintenance again. Yes, I said decades. You may need to add a bit of grease or oil from time to time but you can do that without disassembling the locomotive again.

Removing and Replacing the pickup shoe

If you need to remove the pickup shoe to replace it, it pries off fairly easily with a slotted screwdriver. Hold the shoe in the upward position and pry on one side, where the hole in the shoe slides into the motor’s base plate. Just pry slightly and the shoe will pop out fairly easily. Be careful not to lose the spring that sits under the pickup.

There’s a wire soldered onto the shoe, so if you replace the shoe, you’ll need to desolder the wire and solder it to the replacement.

To replace the shoe, slide one side onto the notch in the pickup plate, then tilt it down to the other end. If it doesn’t clear the notch, spread the pickup slightly with either a pair of needlenose pliers or a slotted screwdriver until it clears the tab, then drop it into place.

Overview of the Marx 666

I put this at the end since you probably already have one if you’re reading this, but if you’re in the market for an O27 locomotive, this one has a lot to offer.

The Marx 666 is a diecast 2-4-2 locomotive, similar to Lionel’s Scout locomotives, but it’s a much more dependable locomotive and its motor is much easier to work on. Scouts were essentially throwaway locomotives; the Marx was designed to run longer and to be fixed when it did finally wear down.

It came in several variations. The two most common varieties are all black, or black with a white stripe and numbering. There’s no particular difference in value between these two variants. A third variant is an olive-drab Army green, worth 2-4 times as much as a black one. A fourth variant, listed in price guides, has the side-smoking motor out of the plastic 1666, but this variant was never produced at the factory.

Sometimes the rear truck is missing, making it a 2-4-0 locomotive. It’s possible a small number of 666s were produced this way, or even as 0-4-0s, to reduce costs. It works fine this way, or perhaps even more reliably, without front and rear trucks to derail, though it looks more complete as a 2-4-2.

The Marx 666 is the second largest steam locomotive Marx produced, and like its big brother the 333, it has smoke. It’s a good all-around locomotive and typically sells for $35-$40 in good running condition, which is a bargain. If you need a good locomotive that will run well on O27 track, the Marx 666 is a very good choice. Marx’s tender is incompatible with Lionel couplers, but the 666 will connect to a Lionel tender so you can run it with Lionel cars.

As for the number, how Marx came to choose the number is a frequent question. Louis Marx was Jewish but attended Episcopal churches, so he was likely aware of the baggage associated with the number. The story I heard is that someone said the locomotive smoked like the devil, so the number was something of an inside joke. Marx was fond of 3-digit numbers. The diecast steamers were all numbered 333, 666, and 999, while the low-end steamers were numbered 400, 490, 591, 592,593 and 594; the tin Canadian Pacific locomotive was numbered 391, and Marx had tin steamers numbered 833, 897, 898, and 994.

I have heard of people filing off one or two digits from the number because they didn’t like it. Given the low cost of the locomotive, the modification doesn’t hurt the value all that much unless it happens to be the rarer Army green variant. Don’t modify a green 666–you can sell it and buy three black ones with the money you get.

Parting thoughts

If this is the first time you’ve tried to fix a train, the Marx 666 isn’t a bad choice. It comes apart easily and there aren’t too many tricks to getting it back together either.

I didn’t learn how to fix trains until I was well into adulthood. When I was a kid, I didn’t have anyone around who had much in the way of mechanical ability to learn from. I started picking this up when I unboxed the trains that had belonged to my dad growing up and some of his stuff didn’t work. I share what I’ve learned (and, let’s face it, what I’m still learning) in hopes of other people being able to use it to do the same thing.

You’ll find it’s well worth the effort. Marx trains are very dependable, and I find it relaxing to watch a train pull its consist around a layout at the end of a long day.

I hope you’ve found this post helpful. If you have, please share a link, whether it’s on a forum, Twitter, or a site like Facebook.

2 thoughts on “How to disassemble a Marx 666 locomotive

  • December 27, 2015 at 9:02 pm

    Super novice 46 YO here,

    My Marx 500 Army Supply Train wheels seized shortly after purchase. Engine ran & lit well for two weeks. Started seizing, but would get out of it with light wheel massage but acted up. Now nothing and I do not want to force anything.

    Any help appreciated. Thanks for the site. I plan on experimenting & learning on some dead engines, but I really want to be careful with the #500. Craig

    • December 27, 2015 at 9:14 pm

      Thanks for writing, Craig. It sounds like the motor needs some lubrication. I’d clean off whatever is on the gears with some mineral spirits, then add fresh grease. I like the Lucas product I reference here, but any modern lithium grease is OK to use. Add a drop of oil to every axle, then do a bit of wheel massage like you did before.

      Worst case scenario, you can swap a motor in from a less expensive locomotive of the same vintage. Pay attention to the pickup shoe–if it’s two pieces, that’s prewar and it will be harder to find than a motor with a one-piece, but it’s still doable. Marx made a locomotive they called the Canadian Pacific (one number was 391, but there were many) that was mechanically identical. As long as you get the vintage correct, it won’t hurt the value of the locomotive.


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