I can't believe this thread came back to life after 3 years!
The Williams name has been around a long time, and I'm not sure what vintage of locomotive is being discussed in some of these posts. But I'll make a general statement (which is the same thing I've been saying for the last 20 years.) It's the gear ratio. It's always been the gear ratio. 98% of the O gauge locos made are geared too tall (fast) for an adult application: continuous operation at modest speeds on a home-sized layout with sharp curves. Going back to the first post in this thread, of course the "old timer" 4-6-0 runs cool, because its motor is operating in a healthy, sustainable RPM range.
Just about every vertically motored diesel ever made (there are a FEW exceptions) is geared too tall. (I'll also observe that the vertical orientation greatly limits the length of the motor AND the available "head room" for a flywheel.) Sure, speed control lets you run them at 5 mph or whatever. But especially if you're also pulling a load, there's a LOT of heat build-up. No easy way to change the gear ratio, and no easy way to remove the excess heat. Maybe real operating exhaust fans? Another gimmick and something else to fail!!
I can only guess that the manufacturers don't want to expend the effort to tame the noise, vibration, and harshness (NVH) issues which are more likely with high-rpm operation. But a properly geared drivetrain is a beautiful thing. Quality engineering design, good materials, and we would be running trains instead of discussing these problems.
