Peter's Model Railroading | Articles | Locomotives | PRR NW2
Couplers

The Sergent Engineering S-scale couplers were released in 2014. I decided to install them on my main switcher engine. Since this coupler is a dead-ringer for a prototype coupler, I took a long, hard look at a photo of the real PRR NW2. I found that the S-Helper Service model, as nice as it is, did not have a coupler box that matched the prototype photo. That bugged me, so part of this article is also about how to make the coupler box area look more like the prototype. The first thing to do is to remove the step area. If you turn the engine over, you will find two small screws that hold this part in place. The photo is of the front steps assembly. For the one in the back, you actually have to loosen up the main screws that hold the shell to the frame, so that you can slightly lift the cab, which then allows the removal of the steps assembly (after you have removed its two small screws). Note that I also took the railings off. These fall out pretty easily.

I had previously installed Walthers ProtoMax HO-scale couplers to this engine, so I removed them. My next step was to figure out how to provide a solid anchor for the Sergent coupler (seen in the background). I found a brass tube that perfectly fit the diameter of the hole in the coupler body. I then drilled a hole in the plastic filler strip that I had already glued to the body (from when I installed the ProtoMax coupler), and I also drilled a bit into the metal of the frame. Next, I used five-minute epoxy to install that brass tube.

Doing a check for coupler height I found that I needed a washer to set the coupler at the correct height. The washer is ever so slightly too thick, but that is the only one I had that fit.

I need a way to keep the coupler in place when the engine is turned right side up. So I used some C-channel strip styrene (scale 12") to start building a box around the coupler. These pieces were also glued to the frame using five-minute epoxy for durability.

I could then use a piece of 0.040"-thick styrene to make the box cover, which was attached with styrene glue. This keeps the coupler from falling out, while still leaving it free to move left and right.

With the basic coupler in place, it was now time to look at the visible coupler area in the prototype photo, which I copied here. If you look at the S-Helper Service model, there is just a rounded shelf over the coupler space. This photo clearly shows a rectangular box around it with a curved top.

So, the first thing to do was to carefully carve off the shelf. You can quite clearly see in the photo what "damage" I did. I put the part in a benchvise and that made it easier (and safer) to work with.

The curved top was simulated by gluing a scale 4" quarterround to a strip of 2x6 of styrene. This gives it that lip at the top that you see in the prototype and does a reasonable approximation to the curve at the top without having to resort to custom filing. I glued these to the steps assembly using styrene glue.

I then cut some more 2x6 pieces to make the sides. This is all that I could do away from the engine, because the coupler is permanently fixed to the frame, so this assembly has to slip over the coupler.

The assembly is back on the engine. I tested it to make sure the coupler has lots of swing space. It does.

Next, I glued a 2x6 strip to the bottom of the two side pieces to complete the rectangular box. Now that it is all in place, I used a scale 4x6 piece of styrene to fill the large gap above the coupler and under the curved section. This makes the whole thing look a lot like the prototype.

This photo shows that I did the same thing to the back coupler area. I used the exact same steps to get it built and installed.

Of course, all that white styrene has to be painted. Trying to match the body color is always a challenge. The last time I was at my local hobby shop, I asked the owner what his replacement for Floquil paints is going to be. He mentioned that he is switching over to Tru-color Paint. I bought a couple of bottles just to test them. One of the ones I bought was TCP-075 "Pennsy Brunswick Green". As luck would have it, after I hand-painted two coats of that paint over the white styrene, it is a perfect match to what S-Helper Service's model color is. Cool! This photo shows the rear coupler area.

(external link: Tru-color Paint)

This is of the finished front coupler area. I also decided to glue the handrails in place using superglue. Those things keep falling off at train shows, and it is just embarrassing. Now I just have to be careful not to break them.

This engine has gone through a number of coupler changes. It came pre-installed with the big AF-compatible claw couplers, which I replaced with the included S-Helper Service Kadee-compatible couplers right after I got the engine. Then, later I changed my fleet standard to the Walthers HO-scale Proto Max couplers. In 2014 Sergent Engineering finally came out with their S-scale couplers. Since this is my main switcher engine for my home layout, I converted it right away (as described above). However, after living with those couplers for a few months, I just found them too difficult to work with. It really made operations on my layout a chore. So, I decided to go back to making the HO-scale ProtoMax couplers my fleet standard again. However, because of all the coupler change-out work I have done to this model, I needed to get more creative with installing the ProtoMax couplers again. I also wanted to preserve the work I had done to the pilots when I installed the Sergent couplers. I had previously installed a shim to get the coupler to sit at the correct height, which you can see in the photo. I also wanted to make very sure the coupler wasn't going to come loose any time soon. I drilled a hole through the shim and into the metal body of the pilot to match the scale 6" plastic tube that just fits the mounting hole of the coupler's draft box. I glued the tube to the pilot with 5-minute epoxy.

I used the drill bit to ever so slightly enlarge the hole of the coupler's draft box. This made it easier to slide the coupler onto the styrene tube. By the way, I build the couplers as per the instructions in the package, and then I apply a small dot of superglue near the back of the body where the body and the lid meet. Capillary action will draw the glue into the body and could potentially get into the metal spring and onto the coupler itself. This has happened a couple of times, so I am now very careful about where I apply the glue. However, without the glue, the coupler can fall apart quite easily. I do apply a tiny drop of superglue to the back of the coupler body where it meets the shim mounted on the engine. This helps to keep the coupler from turning left or right. The thing to remember is that the ProtoMax coupler's outside mounting holes don't quite line up with S-scale mounting holes, so you cannot use them; if you do, the coupler will not sit centered on the car or engine.

Since there was no real sturdy way for me to mount the coupler to the body (if I flip the engine over, the coupler could potentially fall down, although the grip of the plastic tube was quite tight), I decided to cut another small piece of styrene and install it on the plastic tube. Once installed, I used plastic cement to glue it to the tube. This provides the means by which the coupler is held in place vertically.

The pilot "wrap" that I had scratch-built as part of the Sergent coupler installation had fallen off when I removed that coupler. So, I cleaned it up and re-attached it with 5-minute epoxy. I also cut off the plastic tube, and then re-attached the bottom bracket that completes the pilot wrapper around the coupler's draft gear box.

With some touch-up paint everything looks as good as new, and the coupler sits at the correct height according to my coupler height gauge. I can now get back to running my layout again.

In 2023 I bought the new Inventive Models brass couplers. These are based off of the Sergent Engineering couplers and work in a similar manner. Since this is now the fifth coupler that this engine receives, it is mostly a very custom, one-off install that I had to do to get this to work. I used the Smoky Mountain Model Works center sill coupler boxes as they are a perfect fit for this coupler, and it makes installation easier. I first removed the ProtoMax couplers I had installed on this engine, which caused some of the add-on styrene parts to break loose (they will be re-attached later). There is only enough length here for the first screw hole to line up, as the space where the second hole sits is awfully close to the swing area of the trucks. So, I installed them with one screw each (provided with the SMMW coupler box), and then applied some superglue to the back of the coupler box and the engine's frame. If this proves to not be sufficient, I can come back and add more bracing.