C&O K-4 Kanawha
NKP S-1 Berkshire
These two models came out at the same time, so I'm going to go ahead and assume they share the same basic internals and cover them both here.
The locomotive chassis is all-metal and fairly minimalistic (with most of the actual heft being provided by the shell). The motor is a coreless Faulhaber #1319. The driveshaft consists of a large flywheel and two short metal pieces connected by a flexible plastic tube. Only one driver pair is geared (the third pair from the front). All the rest of the drivers are turned by the cranks. All four drivers are sprung, which presumably makes for quieter running and better contact between the drivers and the rails. All gearing is metal. Right-rail pickup is provided by three of the right-side drivers, as well as the right rear trailing truck wheel. The #2 driver pair is equipped with traction tires (a non-TT driver set is included in the box should you wish to trade more pickup for less pulling power). Left-rail pickup comes from the six left-side tender wheels. Current is conducted from the tender to the motor via two stiff wires firmly soldered to the drawbar (a nice improvement over the usual "one floppy wire" system normally found in old N scale steam). A non-directional headlight is wired to the motor and mounted inside the shell. The pilot coupler is a dummy (non-operational) knuckle (although it does pivot). The tender has no coupler, although a MT-friendly pocket (with pre-drilled hole) is provided. Wheels are low-profile, so no problems on Code-55 rails.
These are fantastic looking models, and with performance to match. Mine runs extremely smoothly and quietly at all throttle levels. The double-wired drawbar (along with the live trailing truck wheel) make for flawless pickup. I had no problems creeping through turnouts. I didn't experience any derailing issues or problems on narrow radius curves either. Pulling power is strong. And it's the flywheel that really puts this thing over the top - slow-speed creep is sensational, and the way it glides to a stop is simply breathtaking. Overall, this is easily one of the best steamers I've ever run (brass or otherwise).
To remove the locomotive shell, first unscrew the screw underneath the pilot truck. Next, unscrew the two small screws on the back side of the cab. The shell should lift up and off at that point. To get at the headlight, unscrew the weight inside the shell and pull it out. This will free up the headlight wires and allow you to completely separate the chassis from the shell.