Locomotive Remotoring
For DCC Operation

I have an old Athearn switcher in which I had installed a Lenz decoder against the roof above the motor. It worked OK but the shell didn't fit propery due to the lack of space. The old motor also had a higher current draw than I would have preferred. This is an area of the hobby that I don't know much about. 

I had remotored an Athearn engine many years ago, but usually shy away from this kind of work. Part of the problem is that I didn't understand how to measure the universals and other parts in order to buy the right materials. I had an old non-digital caliper made by Pacific Fast Mail that measured only in HO scale inches and I never mastered measuring the fractions.

Bill Payne, fellow member of our Nottawasaga Model Railway Club is good at this stuff so he led me through the process. He began by giving me a lesson on how to use an electronic caliper with digital display.

Electronic caliper measuring diameter of motor shaft
Mastercraft electronic caliper

Canadian Tire had Mastercraft electronic calipers with digital display on sale for less than $10. A caliper can be used to measure inside dimensions like the space in the Athearn shell and the depth available. It can also be used to measure wire for handrails, grab irons, stirrup steps and to find the right size drill bit. It can be used to check the size of wheels when buying replacements. In this case we needed to confirm the motor shaft diameter and ascertain the gear box shaft diameter so that a flywheel could be installed and the universals could be matched. I never quite understood how to read the NorthWest Short Line (NWSL) catalog to order the correct parts. As Bill explained, the key is to choose universals that have the same size ball and socket cups for interconnecting. 

He prefers the smaller balls listed.

For example, if you check the nwsl.com website and look for the table that lists universal couplings (it's also in the Walthers catalog), you'll see that a typical flat can motor with a 2 mm shaft could use part 482-6 that comes with additional cup sizes for 1.5 mm and 2.4 mm shafts.  The ball diameter is 1/8". 

Ball dimensions can be combined. A 2.4 mm fits most 3/32" shafts. If you want to use a different ball size, then look for another part number that will let you connect to the shafts in question. The Athearn switcher had a larger shaft at the gear box than the 2 mm shaft of the Sagami motor.

So, it's not as complicated as I thought. NWSL also sells prime mover upgrades for Athearn diesels and there are lots of notes on their website. Other upgrades are listed for Roundhouse and other engines.

While we're at it, let's consider measuring with a vernier or micrometer. This is from Bill Payne's clinic at out club. A vernier handles larger sizes. It is normally for up to 6 inches but can go up to 24 inches. 

A micrometer is for handling much smaller sizes, normally in 1 inch increments. O - 1" is a typical range. If the basic size is 1" (inch), then 1 divided into 10 divisions would be 0.100 (thousandths). Each 0.100" divided into 4 divisions of 0.025 would give you 0.050.

The digital caliper I bought can measure in metric or in inches. NWSL gives both measurements in their tables. Sometimes you need to switch back and forth depending on where the part was manufactured. Some countries are only metric. 

Canada is metric. The U.S. didn't convert. The Athearn gear box shaft was not designed as metric so you need to convert the measurement. The NWSL table makes it clear. Playing with the caliper has removed some of my confusion and fear. 

So to recap, the calipers indicated that the Sagami motor I was going to use had a 2 mm diameter shaft and that it would fit the space I had.  The dimensions were listed on the motor's instructions sheet but for this purpose I assumed I had lost the instructions and had to discover the dimensions for myself. Because the old Athearn gear box tower had a much larger shaft it was a matter of matching up the connecting bits, cutting where necessary to get a good fit. We had to shorten the drive shaft at one end of the motor. There was only space for one flywheel. The shaft was cut with a Dremel disc. 

We attached an aligator clip as a heat sink between the motor and the cut line and did the cutting in several passes so as not to overheat the motor. We then blocked up the motor with scrap styrene and wood so that we could finalize the location of everything.  The connecting plastic rods also had to be cut so the ends with the balls had a good fit in the grooves of the plastic cups on the shafts.  We rotated the balls and cups so that the protrusions and slits were at 90 degrees to each other.

The flywheel was a 3/4" diameter, 3/8" long brass flywheel for a 2 mm shaft that fit the Sagami shaft. It is made by A-Line, a division of Proto Power West. It was secured with an extra drop of Sinbad acc glue after being pressed on the motor shaft.   

When all was done the motor was floated in clear silicone bathtub caulk and held in place for curing by strips of styrene as shown here. The caulking ensures isolation of the motor from any metal parts of the locomotive.

Locomotive remotoring with silicone bathtub caulk
Athearn engine remotoring

The second photo from the side shows how all the parts line up. There should be a slight tilt to the universal joints as is visible here. The electronic calipers allowed us to find the optimum distances. Then the setup was "eyeballed" from both sides and from top to bottom and end to end.  

Side view of this locomotive remotoring in an Athearn switcher
Athearn locomotive remotoring

I added some more caulking after 24 hours and then allowed the locomotive remotoring to cure for several days. The final step was to let everything settle in by running the engine in both directions on my test bench. I ran it on DC by clipping wires from a power pack directly to the motor leads. The final step was to reconnect the DCC decoder and put the engine back in service. I now feel confident that I can tackle a few other engines.

Bill Payne and I got back to working on remotoring locomotives so that I could get the HON3 narrow gauge section of my layout back into service.  Our next project was to remotor a small 4-6-0 engine, SP #9.  This meant replacing the old open frame motor with a small can motor. There wasn't much room inside the tender. This is a brass tender-driven engine. We used the calipers to check for clearance and I ordered a single shaft motor from NWSL.

  The motor measures 12 x 16 x 27 mm. The new part number is 1627S-9 (old number 12270-6). The shaft diameter is 1.5 mm. There isn't room for a flywheel. I'll have to rely on decoder programming for smooth operation. We had to shorten the shaft which we did with a Dremel abrasive wheel so there was room for the couplings. NWSL has a page of shaft couplings driveline universals so it is only a matter of checking the shaft diameters and using the appropriate couplings. These are a press fit. You can add a dab of CA glue to secure them if you want to be extra sure after everything is lined up and working correctly.

The first silent decoder we tried was too big. We used an 8-pin plug but even hard-wired it wouldn't fit. I bought a Digitrax Z scale decoder DZ123 that has 1 amp peak. This is more than enough for the draw of the can motor. Although it is Z scale it can be used in N and HO scale conversions as long as the amperage draw can handle it. This usually means replacing the old motor. We didn't attempt to hook up lights because this would be a very tricky operation and would probably involve sourcing new castings. Drilling out the old headlight and routing wiring is problematic. I'll run the locomotive "as is" for now. It has a tendency to stall out on my old Shinohara dual gauge turnouts that pre-date DCC friendly turnouts. I may try building a Fast Tracks Code 70 dual gauge turnout to see if that solves the problem. I don't have a jig for that and there are other more pressing projects on the workbench. My standard gauge engines are running through the turnouts OK so it may be a problem with this particular locomotive. Two steps forward, one step back!

This was a relatively straightforward remotoring job. Bill and I followed by tackling a shay conversion that presented some heavy duty remotoring challenges.

Here's a photo of SP #9.

HON3 Southern Pacific #9 ready for DCC service
hon3 brass locomotive remotoring


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