This was the first N scale diesel rendered in brass (not counting those weirdo Gem/Bachmann F9s and GP40s that came out in the 70s). Unfortunately, like the rest of Kumata's line of early N scale brass locos, these are not very good runners.
The chassis is simply a rectangular hunk of brass, and a relatively flimsy one at that. The fuel tank is also a solid hunk of metal (permanantly attached to the chassis) and provides much of the model's weight. Each truck only picks up current from one rail. Three wheels per truck collect current (no traction tires). Current is transferred from the truck assemblies into the worm gear towers. The forward gear tower then transfers current to the motor through the chassis itself, whereas a wire routes current from the rear tower to the motor. The rear tower is electrically isolated from the chassis by virtue of a thin plastic gasket and nylon screws. The motor is an open-sided / straight-wound 3-poler with dual driveshafts. The forward driveshaft connects directly to the forward worm. The rear driveshaft is a multi-piece affair with a couple of plastic joiners in the middle. Two axles on each truck are geared and all gearing is metal. The trucks are held inside the worm towers by knock-out pins (which are really hard to pull out). Wheels are low profile, so no problems on Code-55 rails. There is no lighting, window glazing or couplers. An ala-carte weight glued to the chassis provides additional weight. A snow plow and sun shades are provided "ala carte" should you wish to install them.
Overall performance is pretty bad. They make a lot of noise and throttle response is pretty uneven. Slow speed creep is iffy at best, and the top end speed is off the charts. As one would suspect, the "one rail per truck" pickup scheme makes turnouts with unpowered frogs impassable obstacles. That flimsy brass chassis isn't much help either. It tends to want to warp out of shape, which can ultimately result in the entire mechanism seizing up if it gets bent too far out of whack. Mine runs best with the shell completely removed, and it won't run at all if I don't leave the chassis screws a bit loose when I do put the shell on. So, ultimately a pretty mediocre model, and one that was rendered completely useless by Kato's SD40-2 ages ago (not to mention the more recent IMRC offering).
These models seem to be pretty scarce these days as they rarely ever show up on eBay (for whatever that's worth). And more often than not collectors seem to be paying prices way beyond their worth as operational models. Go figure.
The shell is held to the chassis by two screws - one under each truck (twist the trucks to reveal them). Once removed, the shell should lift right off.
Reviewed: 1/83 Model Railroader ("It was big news in N scale when Hallmark announced a brass version of the SD40-2. Now the engine's here, and it's a good one. As far as I know, this is the first fabricated brass N scale diesel. Several brass diesels were offered 10 to 12 years ago, but these were one-piece brass investment castings made using plastic body shells as patterns. Hallmark's SD40-2 is made from a variety of sheet, coined, and cast brass parts, like the HO diesels we're accustomed to seeing. I checked the model's dimensions against (drawings) and found them to be within a scale inch or two in almost every instance. There's one slight discrepancy: the trucks on the model are set about 18" further from the ends than they are on the prototype. Visually, this is undetectable, and I assume it's a small compromise made so the model's trucks would swing without jamming against the end steps. And swing they will - the engine runs through 7.5"-radius curves with total ease.
The model is made by Kumata of Japan. I found the workmanship to be quite good throughout. Only tiny patches of excess solder appear here and there, and these should disappear completely once paint is applied. The model's mechanism is simplicity itself, a big plus in my opinion. You get at the innards by removing the body shell from the sheet-brass floor. The body is held on by tiny Phillips head screws, one located at each end of the floor and visible once the truck is swung to one side. The trucks are held in the metal gearboxes by metal pins. These look like knock-out pins of the sort often seen on N scale locomotives, but I pulled on them as hard as I could with pliers and couldn't get them to come out... Two axles on each truck are equipped with brass gears. These are driven by a pair of plastic reduction gears, that are in turn driven by a brass worm. The worm gears, mounted in line with the motor, are also brass. The simple, five-pole, open-frame motor is unassuming, but it does a good job. The low speed might seem high, but it ran quietly and smoothly on our test track... On one side of the locomotive the electrical pickup is by one truck only. I've had no problems with stalling... Most of the locomotive's weight comes from its fuel tank. It's a solid casting of heavy metal, probably lead, that has been spray painted gold. Included in a separate envelope are a brass snowplow and a pair of window awnings... This is a good-looking, and best of all, quiet and smooth-running locomotive that will pull 30 cars... Hallmark plans more brass N scale engines in the future, and if they come out as good as this first one, we're in for lots of treats. $149.95")