by Kevin Kelley
Required Parts and tools
Kadee #4 coupler assembly with draft box
Rectangular jewelers file
1 sheet 600 grit emery paper
fast setting epoxy
small piece of spare styrene
Adding front couplers to the Athearn Mikado is a frustrating and delicate operation—one that should have been taken care of by Athearn during the design of the model (a working model should work in all relevant ways). However, the locomotive is one of the nicest running engines available and is a practical requirement for prototypical operation on just about any steam era railroad so it’s worth the effort. I recently read a description for adding front couplers and wanted to relate my own experience that I found to be entirely satisfactory.
First I should mention that the Mikado is available in either footboard pilot and road pilot. I started with the road pilot and have no experience with the footboard version. Secondly, the Athearn Genesis 2-8-2 light Pacific comes standard with operating front couplers, and since the footboard/road pilot on the Mikado is attached to the frame with jewelers screws, there is an outside chance that the Pacific pilot (which may or may not) be attached in the same manner, could possibly be swapped out easily. This might be something to look into, but I just went ahead and did the operation to my existing locomotive. Note also that I did not measure the final results with the NMRA coupler height gauge, but the coupler install appears to be within tolerances (maybe (very) slightly high), and works well with all my rolling stock.
Choice of couplers
The article referenced above (which was my starting point) used the Kadee #39 coupler, which is an overshank (high shank/low coupler knuckle) with the pentagonal spring face that is common to the #5 coupler. The author had filed the pentagonal area and the opening of the pilot draft box with a jewelers file in order to pass the coupler into the draft gear box opening while leaving enough material on the coupler to pin the coupler in place with a small screw. I assume the screw would need to be filed where it exited the top of the pilot deck or covered with a scale tool box or something. In any event, the screw and the fact that the coupler would be fixed in place (no side to side swing) seemed to be sizable drawbacks to the procedure. The following method eliminates both.
For my project I used the Kadee #4 coupler. This coupler is a standard height design (neither over nor undershank) with a centering mechanism that consists of two nubs on either side of the shank that pull against similar nubs on the inside of the draft box. A small coil spring is placed in a slot at the rear of the shank and pushes against the draft box pin to center of the coupler. This design is the narrowest of the Kadee couplers and would fit through the factory coupler draft box opening were it not for the nubs.
Start by removing the stock dummy coupler by pinching the rear of the coupler with needle-nose pliers while pulling the coupler away from the pilot deck. Next, file the pilot coupler draft box opening (for width only) with a rectangular jewelers file. Be careful not to file too much….you need it to be paper thin, but it’ll be a delicate deal. At this point, make sure to round off the rear of the pilot coupler box under the pilot deck. The idea here is that you don’t want the coupler nubs to hit the corners of the opening as they toggle back and forth in the modified Kadee draft box assembly (you’ll eventually be chopping the draft box down to the point that the nubs on the coupler are actually exposed on the front side of the Kadee coupler box nubs). You’ll also need to file the nubs on the coupler down a little (as little as possible). The nubs will still have to work with the Kadee metal coupler box, so start off by just removing the radius of the coupler nub on both sides and work from there. Before you insert the coupler into the pilot, make sure one more time that the nubs still work with the stock Kadee coupler box. Toggle the coupler back and forth to make sure that the action is correct and the coupler doesn’t get caught in any funny ways. Simulate the spring loaded forces on the coupler and makes sure it all works smoothly. If not, toss the coupler and start with a new one! Eventually, the coupler will be able to be forcibly inserted into the pilot coupler box. Try inserting it at a slight angle as it will fit better that way. Once you’ve inserted the coupler you don’t want to have to take it out, so make sure it’s good to go first.
Cutting and modifying the Kadee coupler box
Once you have inserted the new coupler, it’s time to start modifying the Kadee coupler draft box. To do this, you’ll have to cut the front of the box off just in front of the pin. I used a jewelers saw to cut the metal box, but I suppose that it could be filed in a vice. Make sure the coupler box nubs are still intact and centering the coupler properly. Test fit the coupler box under the pilot deck. Angle the coupler box pin and slide into the coupler slot. You’ll begin to see how it all fits together now. You’ll also see that the coupler box doesn’t mate to the bottom of the pilot deck very well due to the plastic ribs on the underside of the pilot deck that are too narrow to nestle the coupler box in between. You can turn this to an advantage though by attaching a piece of styrene as a spacer between the Kadee box and the pilot. I did this by cutting a rectangle of scrap styrene about 1/32nd of an inch less in width than pilot ribs and about the same length as the cut down coupler box. By making the spacer narrower than the ribs, you’ll be able to align the box more accurately. The spacer will need to be epoxyed to the coupler box and I started by sanding the back of the coupler box with 600 grit emery paper. Set the box on a sheet of emery paper and run the box over the surface like a sanding block. Do the same with both sides of the styrene spacer. Epoxy the spacer to the coupler box, but be careful to shift the spacer back slightly on the box so that there is about 1/32 of an inch overhang to the rear of the box. This is because where the ribs on the bottom of the pilot meet the “cowcatcher” there is a small radius and this radius will tilt the box down preventing it from seating properly. Take a look and you’ll see.
Installing the coupler draft box and coupler
When the epoxy is dry, try test fitting the box in the pilot. You’ll want to have it as far forward as possible, but make sure the coupler nubs don’t foul on the pilot coupler opening (this is why you rounded the back of the pilot opening earlier). Extra coupler springs are supplied, so assemble the whole thing and test the movement of the coupler. Installing the spring with the slug inside is tricky. Try using an Exacto knife wedged between the spring coils to manipulate the spring. Tilt the whole engine nose down so the slug doesn’t fall out. When you are comfortable with the position of the draft box, disassemble the spring and box, and prepare to fasten the box to the pilot. I initially used plastic solvent for the styrene to styrene connection (spacer/coupler box to pilot), but found out that this wasn’t sufficiently strong, so I would recommend epoxy for this as well. When everything is dry, you’ll need to assemble the coupler with spring and fit the cover over the whole thing. Paying attention to the Kadee instructions since there is a front and back to the cover, cut the coupler plate with a jewelers saw just ahead of the hole. In my case there was only a microscopic amount of material on the front side of the hole when I was done. The Kadee method of using a screwdriver to peen over the head of the pin would probably work alright if the full plate was being used, but since the hole is now offset so severely, the back of the plate doesn’t stay down sufficiently. I ended up epoxying the plate on, but I erred by allowing epoxy to seep into the box, pinning the back of the coupler to the box. I was subsequently able to break the coupler free, but it was almost a disaster. I would recommend a dab of epoxy on top of the pin to hold the coupler plate in place. It doesn’t take a lot of abuse so I’m sure it’ll be a fine solution. Now you have a working coupler that has enough play that derailments won’t occur at switches and such. Good luck.