I had better call Ed Yungling tomorrow, first thing, and let him know that the Cab Forward is in imminent danger of valve gear failure, and will have to be immediately rebuilt, as it was built to scale and must be at least 30 years old. I will also let Don know that he should consider going thru the scale valve gear on his GS-1 while he is doing all that beautiful detail work. Now he will be able to easily make the valve crossheads and guides bigger while he has the cylinder block off the chassis. His valve gear is close to 20 years old. And thank god I read this before I run my GS-4 again and have the big end of the eccentric rod let go while running at speed. It was scaled directly from the Lima blueprints. I will let Ed know that he had better stop this practice of scaling valve gear from railroad blueprints. And anyone else out there with scale gear should immediately bad order their locomotives, have them towed dead to the backshop and inspect for repair before any more damage occurs.There is a pitfall in oversimplification! A locomotive on an 1/8 scale may have its volume reduced to 1/512 but not its weight! For instance a 1:1 boiler plate thickness of say 3/4 inch is not scaled to 3/32 but more, adding weight.
Regarding the rods in a locomotive, the above reasoning disregards the fact that rods are pulled and pushed 50% of their working time. Since you do not want your eccentric rod to deform it should be stiffer to avoid buckling. (for an explanation of buckling see the Wikipedia page). Since the buckling force formula has the rods Moment of inertia divided by the square of the rods lengths, this goes wrong if the diameter and length are scaled to 1/8 of the original. The inertia moment of a round rod is pi*d^4/64 and since 1/8^4 is only 0.000244 it should be clear that a scaled rod cannot withstand a scaled pushing force! So there is very much physical evidence for a heavier model valve motion.
P.S. Dorian, here is a link to an outfit that does quite a bit of gauge 1 work and mods. I have not had any dealings with them, but it may be worth a phone call.