This GP50 model was a rather short-lived offering from Kato, consisting of the original 1988 run and a couple of special/limited runs (1989 and 1991). It hasn't been run since, and given the now-dated design, I suspect we've seen the last of it. And I guess only Kato knows why it was produced in such limited numbers, as it was certainly a widely lauded model "back in the day" (and still is, for that matter).
The GP50 chassis/mechanism is quite similar to the one Kato used in their revised (1988) GP38-2 model (although they are by no means identical). One major difference between the two models (at least in the performance department) is that these GP50's are much less likely to have their drivetrains get out of alignment and go all "barbershop razor" on you (or so I've been told).
The chassis is all-metal and really heavy. The motor is an open-sided 5-poler. The worms are brass assemblies with flywheels on either side (IE, there are four flywheels in this model). All wheels are blackened, geared and provide pickup (no traction tires). The truck gearing is all plastic. Directional lighting is provided by a metallic PC board screwed to the top of the chassis. Couplers are truck-mounted Rapidos (IE, open pilots). Wheel flanges are low-profile, so no problems running these on Code-55 track.
Performance is outstanding in every way - smooth, quiet, excellent throttle response, great slow-speed creep, perfect pickup, and pulling power to spare. Oh sure, the top-end speed is ridiculously high, but that's just the way things were back in the 80's and 90's. My only real complaint with these models is their "Chinese puzzle box" complexity. Dismantling the mechanism is much more difficult than taking apart a more traditional "vertically split-frame chassis" diesel.
As noted above, these models originally came with Rapido-style couplers and open-pilots. However, at this point in history it's becoming increasingly difficult to find one so-configured. Most of these have long since been converted to Micro-Trains couplers (said conversion kit also coming with full pilots).
Trivia - Kato GP50 shells can be mounted on the Atlas GP40 (et al) chassis without modification (a quick and easy way to get a DCC-Ready GP50).
Removing the shell is pretty simple - just unhook the handrails from the cab and then pull up on the shell. It should lift off easily (the battery boxes will come loose, but that's to be expected). The walkway/handrail assembly is firmly fixed to the chassis, so don't expect that to come up with the shell. Getting that thing off basically involves dismantling virtually the entire model (whee).
For complete disassembly instructions, check out Ron Bearden's article in N-Scale Magazine (July/August 1990, Vol 2, Issue 4, p. 35-37). And if you can't find a copy of the actual magazine, it's also available on the N-Scale Magazine. Volume 1 CD-ROM.
Reviewed: 10/88 Model Railroader ("Last year Kato, widely praised for the superior locomotives it has built for Con-Cor and Atlas, introduced the first N scale locomotive sold under its own name, the highly acclaimed GP38-2... Now the firm has followed with a GP50... Kato's N scale version of the GP50 meets the high standards we've come to expect from this Japanese firm. The detailing is exquisite - you have to look at the model under a magnifying glass to appreciate how delicate and fine this work really is. Look carefully at the fans and you can see the individual blades under the grills. The horns are scale and the handrails nearly so. The model checked out nicely in every dimension and detail against prototype drawings and photos... The paint and lettering on our two samples (SF and UP) were excellent, except for the deck and handrail assemblies. The deck assembly for the SF unit is cast in black plastic, whereas the deck should be blue, with a black fuel tank and yellow handrails and side sills. The deck and rails on the UP are cast in a gray that is correct, but the side sills should be red. Also, the trucks should be gray to match the body. As I learned with Kato's SF GP38-2, painting the deck properly is a problem because ordinary model railroad paints such as Floquil's don't stick well to the slippery plastic Kato uses...
"Performance is excellent. The engine is particularly adept at slow, realistic starts and slow speed running. It starts running at 2.6 volts, which is also its minimum running speed... To get at what's under the hood, pull the handrail ends away from the cab sides, then lift the body shell up and off (the deck will stay behind). The battery boxes under the cab sides will fall off, so it's a good idea to take a minute and cement them to the shell... The mechanism is nearly identical to the second-generation GP38-2 mechanism. (Early production Kato GP38-2s had a different drive shaft design with no bearings supporting the ends.) To further disassemble the metal frame, remove the four screws down through the top. (These also hold the printed circuit for directional lighting.) Then pry the plastic tabs at the ends to free the deck casting from the metal frame... The motor features a five-pole armature and has plastic universals at each end. Each worm gear is a brass turning with an integral flywheel at each end, for four flywheels in all. Bronze bearings support both ends of each drive shaft and are held in place by plastic fittings that slip into the frame.
"The trucks are held in by metal clips under the plastic deck and can be removed without disassembling the unit if you pry with a small screwdriver between the top of the truck and the clip. All the wheels pick up electricity, and there are no wires to twist and break, as the circuit is completed by contacts from the wheels to the truck-mounting clips to the four assembly screws. (The plastic deck insulates the trucks from the metal frame.) The wheels, blackened for realistic appearance, are driven by a series of plastic gears in the type of gear tower usually found in N scale locomotives... Finally, note that the model is produced both with dynamic brakes (characterized by the brake blister atop admidships) and without them (correct for the Mopac and UP units). With a new engine that's as good - maybe even better - than the GP38-2's, this Kato GP50 is an excellent addition to the N scale locomotive roster. Our only recommendation is for the company to keep those fine engines coming. Evidently they intend to do so, as they've announced an F3 to be out soon. SF, BN, C&NW, MP, UP, Undec. $64.95")