Re: Problems unknown.

Hi Coke:
You tweaked my interest about how three seemingly identical engines ride so differently. Of course, as you pointed out years of use ensure that they are not really identical anymore. In fact, erecting floor high jinx at Alco probably meant they never were really "identical".
In my mind the K-28, K-36 and K-37 classes have cab arrangements that easily amplify rough motion precipitated by the running gear, especially on bad track. These engines have long trailer truck frames so the cab is kind of like being at the end of a long whip. When I was on the #487 it seemed like we were on a bumpy gravel road almost as soon as the wheels started to turn. All of this is accentuated by the fact that the running gear on these outside frame engines is probably farther outside of each rail than the distance from the track centerline to the rails. This means the inertia forces (due to unbalanced weights not steam forces on pistons) tend to swing the engine about its center of gravity from side to side at any appreciable speed. Also the relatively short, high angle main rods tend to bob each side of the engine up and down like a grasshopper walking down the road. These forces tend to cause the cab to move down the line like a spiral with assorted jerks and thuds due to lost motion in the running gear and motion work. The 480's and 490's have much heavier running gear than the 470's so they tend to have larger unbalanced forces that are more difficult to control. Also the 480's and 490's have a 24" stroke and the 470's have a 22" stroke. All classes have 44" drivers. The shorter stroke of the 470's tends to produce a smoother running engine.
It is nearly impossible to tell what causes one out of three engines to ride significantly worse. However, it can probably be traced to three areas. First, if the valves are badly out of time huge compression pressures on one side can develop when the engine is hooked up at short cutoff. This causes the engine to "hump" and can get bad enough in lighter engines to cause discomfort in the cab. Second, If the spring rigging, the fulcrum pins and the level of the engine are substantially out of whack the suspension system will not respond properly, thus the enginemen's butts become the primary shock absorbers on the locomotive -- this can cause varying degrees of discomfort. Third, the centering mechanisms on the pony and trailer truck suspensions are critically important relative to stabilizing the engine horizontally and, to a lesser degree, vertically. I sincerely doubt any of the n.g. Rio Grande engines have trailer truck suspensions that are anywhere close to original manufacturer's configuration. This means the cab, being at the end of that long trailer truck frame reacts about the same as a flea riding on a dog's tail.
While all these things may materially affect the locomotive's ride characteristics and wear adversely on enginemen's nerves it is equally important to note that such things also acclerate wear that drives maintenance costs up dramatically and ensures early retirement to the shop for heavy repairs to things like tires and hub liners.
A reciprocating steam locomotive is a kinematic kailedescope of massive forces that are dancing around the machine elements in constant interaction with one another. It always amazes me that anyone could build something like a 350 ton 4-8-4 that could cruise all day at 100 mph and not tear itself to pieces. The n.g. engines cannot go that fast, but their drivers can nearly make the same rpm and that is where the inertia forces come from.
Bill Petitjean