Articles - Arnold S2
09/16/2005
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The S2 was a yard switcher built by Alco (American Locomotive Company). The Pennsylvania Railroad acquired their first S2 in 1950. Their engines were rated at 1000HP. The PRR class was AS10 (Alco, switcher, 1000 horsepower). A prototype photo of road number 5642 can be found on the Fallen Flags web site. During WWII Alco was designated as the main company for building yard switchers, so most railroads wound up with either an S1 or an S2. They were very reliable and many survive even to today (source: Model Railroader Magazine, March 1984, pg. 33).

The Arnold model was released in 1991, with "Rapido" couplers and very large wheel flanges. It is a very nice model. The model weighs 2.3 oz (66g).
Arnold S2 Arnold S2 Arnold S2

Coupler Conversion

This next section describes how I converted my Arnold S2 from the standard Rapido couplers to the Micro-Trains truck-mounted couplers, part number 1049. I used a magnifying visor, two different sizes of jewelers screwdrivers, an exacto knife to remove the flash off of the plastic parts, and a pair of tweezers to hold the coupler. The first picture shows coupler conversion kit.
Arnold S2
The first step is to use a small jeweler's screwdriver and remove the two screws in each wheel assembly.
Arnold S2
The gear cover comes off and the Rapido coupler with the spring are clearly visible.
Arnold S2
Carefully remove the coupler and the spring. The spring might jump out!
Arnold S2
Here are the parts you get from Micro-Trains. At the top are two "adapters" that still need to be removed from their sprue. These will house the original spring. The coupler and the T-shank coupler are two separate pieces that need to be attached to each other before placing them in the locomotive. (What I was missing were the two springs)
Arnold S2
Either my set didn't come with the springs, or (more than likely) I lost mine, but I had to borrow two springs from another Micro-Trains coupler conversion kit. That kit contained a spare set of springs, so it worked out great. This next photo shows the adaptor, spring, and coupler halves in place before replacing the gear cover plate. It takes a bit of patience, but it will snap into place easily.
Arnold S2
Here is the finished product. The first conversion took about an hour (my first MT conversion). The second wheel set conversion took about 5 minutes. Overall this project was very easy and required no adjusting or filing on the locomotive.
Arnold S2

Motor Conversion

If you want your model to have a smooth-running engine, contact Hans Starmans (web site appears to be gone) and ask for the Arnold S2 motor conversion kit. I highly recommend it. It is not cheap, but I think it is worth it. This is a close-up shot of the motor. It comes complete with good, accurate, and detailed instructions on how to replace the motor.
Arnold S2
I completed the conversion to the new motor in about 2 hours (taking my time). Here is a picture of the locomotive before the heart-transplant. The tools needed are a pair of needle nose pliers, a small vise grip, two small screwdrivers, and optional magnifying glasses. The vise grip is needed to hold the old motor while you pull off the worm gears.
Arnold S2
The Arnold model itself comes with two diagrams in the box (if you bought the original unit). One shows how to take the locomotive apart, and the other side shows an exploded diagram of all the parts. These were very helpful. The Starmans' motor comes with textual instructions on how to take the locomotive apart. Both of the sets of instructions together made for a complete and easy-to-follow picture. My article adds photos. The first thing to do is to take the fuel tank off. With a very small screwdriver pry between the body and the fuel tank part.
Arnold S2
Once the fuel tank is out, there are two pieces of plastic that slide toward the middle of the locomotive. This frees up the wheel assembly.
Arnold S2
Push the plastic locks back slightly and pry them up using a small screwdriver in the direction shown in this photograph.
Arnold S2
Removing the cab was a bit of a challenge. There is a lip that slips in between the walkway and the printed circuit board. Also, before loosening that, pull out the handrails that are attached to the cab from the main body. They snap loose, but require a little effort with a pair of needle nose pliers.
Arnold S2
On the front of the locomotive you will find a small screw. This holds the walkway to the main frame. When you remove the screw, the printed circuit board can pop loose and the V clip that holds it in place can fall out, so be careful not to loose that clip.
Arnold S2
Here is a photograph of the body, frame, and motor with worm gears. This is an important picture. I actually used this photograph to re-assemble the new motor and worm gears. The worm gears are really extracted springs - an ingenious (but potentially flawed) system (some people have reported problems with this drive system; I never had any problems). Follow the instructions that came with the motor for taking the worm gears off of the motor - very important.
Arnold S2
Here is the old motor removed from the main body.
Arnold S2
I placed the motor in the vise grip just tight enough so that it wouldn't slip. I placed a bag over the worm gear to catch it coming off the motor. The first one went flying off, and so for the second one I came up with this contraption. Needless to say I found the first one again, but it did generate an increase in heart rate! ;-)
Arnold S2
The following photos shows how the worm gears are placed on the new motor.
Arnold S2
The motor comes with a piece of brass foil. This needs to be placed in the body before inserting the motor. Be careful because when you press it in too far, it becomes like a spring and it will jump out (again, speaking from experience!). Update: I received an email message from Hans Starmans stating that the brass foil was supposed to go in length-wise, not the way I did it (i.e. turn it 90 degrees from the way it is shown in the photo below). It seems to work just fine, so I left it the way I did it.
Arnold S2
The next step is to assemble the unit again.
Arnold S2
The finished product. Before final assembly I tested the locomotive. I placed it on a test track with the cheap starter set transformer and it ran great. In the forward direction it made a slight noise. I removed the wheels, inspected the worm gears, and replaced the wheels. After finishing the complete assembly, I tested the locomotive again. It made no noise at all this time. Well worth the money and the effort, if you like slow-moving switchers. It runs great and makes little to no noise. Both of these features are a great improvement over the stock behavior.
Arnold S2

Replace Pilot

As shown in another article, I had previously converted this engine to N-scale couplers which were mounted in the truck. I wanted to now install body-mounted Z-scale couplers. To do this conversion, I used the Sunrise Enterprises N-211 Arnold S2 Pilot (no longer sold by the company) for body-mounting. You might be able to find this kit on eBay or in some small hobby shop that stocks old kits. The kit comes with two pilots and pretty good instructions. The pilots are a perfect fit for the Micro-Trains MT-1015 couplers (N-scale couplers). However, for Z-scale couplers some extra work is involved. The opened package and the locomotive are shown here.
Arnold S2
See one of the other articles on how to disassemble the engine. This project is not for the faint-of-heart. It does require some cutting and patience. The pilots have a slight recess that perfectly matches the small flange in the S2's body. The pilot's horizontal steps then slide right onto the filed-off area. The two pilots are slightly different. Try them both, but only one will fit nicely on one side of the body. Note that this part of the engine's body is some sort of zinc-alloy, not plastic.
Arnold S2
The pilots are test fitted in the next photo.
Arnold S2
This close-up of one of the pilots shows the hole I drilled in it to take the small screw that comes with the coupler. There is an indent in the casting that is probably a good match for the N-scale coupler. For the Z-scale coupler I had to drill the hole right on the front edge of the indent. I pre-drilled the hole with a #73 drill bit and then a #67 drill bit. I used the tap that comes with the MT coupler conversion starter kit.
Arnold S2
The pilots are cast for the MT-1015 coupler. The Z-scale coupler is wider (and longer). I needed to file down the flanges, or lips, on the inside of the pilot coupler cavity. The photo below shows the coupler before this filing.
Arnold S2
And here is the coupler installed with the screw.
Arnold S2
The problem with the Z-scale coupler is that it is too long, as can be seen here in the photo. The Sunrise pilots just barely clear the trucks as it is, so the coupler is definitely a problem.
Arnold S2
The radical solution? I simply cut off the rear end of the coupler. I was afraid that the coupler would fall apart, but it didn't.
Arnold S2
Here is the extremely close tolerance. Again, I was worried, but when I took the engine to my track, it ran just fine through a #6 turnout.
Arnold S2
Although the photo above shows the truck already in place, there was some work to be done to the trucks. The older coupler box needs to be cut off. This photo shows what needs to be cut off from the gear box cover.
Arnold S2
And this photo shows what needs to be cut off from the truck frame itself.
Arnold S2
The pilots have been installed and glued to the metal walkway using 5-minute epoxy.
Arnold S2
Here you can see the close-coupling that Z-scale couplers provide. The couplers installed using the Sunrise pilots puts the couplers at just the right height (note that the engine's cab has not yet been installed in this photo; I was doing a quick check).
Arnold S2
Here's a shot of the front pilot.
Arnold S2

Lower the Flanges

The flanges on the Arnold S2 are huge. Period. They will work on code 70 and taller track, but for code 55 and, especially, code 40 the flanges need to be lowered. There are companies or individuals who will do that kind of work for you. Another option is to purchase new wheel sets from NWSL (#2680-6 for $19.95). The third option is to turn the flanges down yourself. This is the option I chose. This was my first time doing this. It wasn't all that difficult. The results were excellent. See above on how to disassemble the engine. I placed one wheel of the axle in the chuck of a cordless drill and held the other against a fine file. Not pressing down too hard, and being patient, eventually the flange was lowered to the desired depth. I checked it regularly against one of the Micro-Trains low-profile wheel set.
Arnold S2
The close-up photo below shows the before, unmodified wheel on the right, and the turned-down flanges on the left.
Arnold S2