Decoder Installation
In A Brass Locomotive

I have an HO scale RS-18 Montreal Locomotive Works (M.L.W.) brass locomotive by Alco Models bought in 1989. It was manufactured in Japan. It has sat in a box and never been run. It is undecorated and needs to be painted. it also needs to work on DCC. I decided to see what I could do with it. This is not an area of the hobby I have much experience with so I approached the decoder installation with some trepidation. Fellow modeller Bill Payne of our Nottawasaga Model Railway  club helped me get started. Here are some of the challenges we faced and how we solved them. This might help you do your own conversions.

I decided not to change the original motor. We checked the stall current and it appeared to be slightly less than the Digitrax basic decoder I had on hand. We used a meter to check the amperage drawn on DC by holding the armature to keep it from spinning while cranking up the voltage to full on a Tech II DC power pack.

The motor was attached to the metal frame with metal screws. The first job was to disconnect the wires from the motor and remove the screws attaching it to the frame. Then we bedded the motor in bathtub caulk while keeping the universals propped up in the same configuration as before. This method isolates the motor from the frame. The clear bathtub caulk was allowed to set and dry for a few days.

I hard wired in the decoder following the standard NMRA convention for the colours. The model didn't have lights so I installed 12 volt bulbs in some brass tubing and used CA glue to secure the bulbs, tubes and brass brackets.

I added 47 ohm 1/2 watt resistors in one lead of each bulb to make them less bright and extend their life. The resistors help to distribute the heat from the bulbs and the brass tubes also act as heat sinks. I could have used LEDs but I didn't have any handy. I avoided using solder around the bulbs.

Setting up the decoder installation
in a brass RS-18 engine
brass engine decoder installation

The next step was to solder the wires from the trucks to the gear towers. When all was done I put the locomotive on my Lenz DCC programming track and programmed in 18 as an address. The address was accepted so I knew I didn't have a short anywhere. So far so good.

I put the shell on the locomotive and retested it on the programming track.

  • It is important to retest on the programming track after each step to avoid blowing the decoder.

This time I immediately got a short circuit. I identified the problem. Although the motor was isolated from the frame, the sides of the motor were touching the brass shell. This would not be a problem if I had remotored the locomotive with a can motor that didn't touch the sides.I solved the problem by wrapping the motor in black electrical tape. The motor is a tight fit. After rechecking on the programming track, I put the brass locomotive on the layout to see how it would run. 

It worked fine on a straight length of track but stalled on the frogs of turnouts. Back to the workbench. The meter showed that there was only 4-wheel pickup, not 8. Like an Athearn locomotive, one tower routed power from the left rail while the other tower routed power to the right rail. 

There was no continuity across the truck as would be expected, but one side was in fact dead.  I couldn't use the frame because it would immediately cause a short. (I tried this without success). It was necessary to find another solution. I didn't want to add track shoes. I've never had much success with them because they tend to hang up on track irregularities. Bill had some phosphor bronze wire that has a very small diameter and is very flexible. I had heard many years ago that other modellers had used this method of improving electrical pickup. 

Adding phosphor bronze wire pickups
phosphor bronze wire pickup

As the photo inset shows, I took a small piece of circuit board tie, filed off the metal on one side, and soldered a wire to it and a short length of phosphor bronze wire. The phosphor bronze wire was cut and positioned so it would rub on the top of the wheel tread. I used CA super glue to affix the small tie block to the bottom of the metal strap that secures the sideframes to the truck. The wire was routed up behind the truck and soldered to the gear tower connection at the other end of the diesel. Then I did the same thing for the opposite side. I now had 8-wheel electrical pickup as confirmed by the meter and on the programming track.

 I placed the engine back on the track to try out the decoder installation. The engine started to work and then shorted out on curves and turnouts. The phosphor bronze wire had introduced a mechanical problem into the mix. The slight pressure was tilting the sideframes causing them to short out on the top of the rail. I fixed this problem by securing the sideframes to the strapping with CA glue. This stopped them from wobbling. I followed this up by hand-painting the sideframes with Polly Scale Engine Black. 

I had already sprayed the locomotive and sideframes with gray auto primer when I had the shell off the locomotive. I had covered the motor, decoder, and all moving parts with masking tape. I had to use a Q-tip dipped in paint brush cleaner to clean the treads after priming. That's why I hand-painted the sideframes.  After letting the paint dry for a few days I added a thin coating of CA glue to act as an extra barrier. I figured if all else failed, I could add a thin layer of styrene to the bottom of the sideframes. Last resort would be to replace the sideframes with plastic ones.

After painting the bottoms of the sideframes and stablizing them with the CA glue, the decoder installation worked OK.  Back on the layout the brass locomotive ran fine on straight and curved track and across the frogs of turnouts without stalling or shorting out. There may be better ways of doing a decoder installation in a brass locomotive that only has 4-wheel pickup, but this experiment seems to have worked.

I painted the locomotive with True Line Olive Green #11 (TLT010014) using my Aztek airbrush. It took several light coats to get good coverage. I did the spraying in our garage. I  added decals and striping from some very old CN Accu-cal Multipak decals. This was very difficult because the decals had dried out and were very brittle. I heated them under a desk lamp for about 30 minutes to soften them a little. This was a tip from Tom at the Credit Valley Railroad hobby shop in Toronto. 

I also sprayed the decal sets several times with Dullcoat to hold them together. I still had a lot of trouble with the curved decals on the front and rear ends of the engine. The striping went on fairly well although it broke in several places. 

I used Badger's Modelflex CN Yellow #11 (16-166) to touch up the breaks. It was a fairly good match. 

My brass RS-18 engine at Utopia East yard
awaiting its first assignment
brass engine cn3702 rs-18

A light weathering with black and rust chalks and some Polly Scale rust/rail brown mix covered some of the mistakes. It looks OK if you don't get too close and nitpick!

I hope this gives you some ideas and a nudge to getting your old brass locomotives off the shelf and into action on your layout.



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