Sunset actually imported three different Trainmasters from two different Japanese manufacturers- one from Northern Alpine Models (Phase 1B) and two from Kumata (a generic Phase II and a Phase II PRR version). I'm sure there's an interesting tale in all of that, but I'll be damned if I know what it is.
Anyway, let's start off by talking about NAP's Phase 1B -
This is a very nice loco - in fact, one of the best running brass diesels I've yet encountered (all the more amazing, given its age). The mechanism is very cleverly designed and actually makes use of a PC board to move current around (as opposed to those nasty old wires used by Samhongsa in their brass diesels). Performance is excellent- great slow speed creepability, great pickup and overall smooth performance at all throttle levels (no doubt owing to the 5-pole motor and aforementioned wireless pickup scheme). And despite the six-axle trucks, this loco has no trouble at all on my narrow radius curves. It does run a little loud (at least as compared to more modern locomotives), but this is only noticeable at high speeds. As is generally the case with brass, this loco has no window glazing and no lights. Interestingly enough, it does come with ala-carte brass knuckle couplers and coupler mounts. I've certainly never seen that before. No traction tires.
So, that's the good 'un. Now let's talk about the Kumata version -
The mechanism here is quite simplistic (and actually quite similar to the lousy mechs Kumata made for the brass Alco diesels Hallmark imported in 1983). The chassis is simply a big hunk of brass (and with nary a PC board in sight). The motor is a cheap looking 3-poler. Right-rail pickup is provided solely by the three right-side wheels on the forward truck (with current transferred to the motor via a wire). Similarly, left-rail pickup is provided by the three left-side wheels on the rear truck (with current transferred to the motor via the chassis itself). None of the wheels have traction tires. The inner two axles on each truck are geared (with the outer axles being free-spinners). All gearing is metal. The wheel flanges are reasonably sized, so no problems on Code-55 rails. There is no lighting, nor window-glazing. There aren't any couplers either.
Performance on these Kumatas pretty much sucks. Yeah, faced with a simple test track, I guess they run well enough. A little growly to be sure, but decent throttle response, respectable slow-speed creep, etc. But wow, throw a few simple curveballs at these guys and things start to go south in a big hurry. First off, the "one rail per truck" pickup scheme makes any turnout an unpassable obstacle for these models. But that's just the tip of the crapberg. When faced with any sort of variation in track elevation (an incline or a dip or whatever), the trucks will come in contact with the chassis. Which is all well and good for the one truck that actually runs its current through the chassis. But the other one? Zap, instant short circuit! In other words, these Kumata Trainmasters are completely useless as operating models (which might actually explain why Sunset went with NAP for the 1B's).
To remove the shell on these models, simply remove the small screws on the bottom. It should come up and off readily at that point.
Grade: A (for the NAP) and F (for the Kumatas)