Re: K37 Throttle

From what we've been able to gather, there are 2 main differences in the design of typical throttle valves/linkages, and those original to the K-37s. For one, the cross sectional area of the proud seat on all throttles is larger than the recessive seat, as if the linkage were to fail this allows the throttle to "fall closed" under pressure. The K-37s proud seats are exceptionally large when compared to the recessive ones, making the valve theoretically safer in the event of a total linkage failure, but harder to open (especially at operating pressure).

This isn't the big reason they seem to be temperamental though, that distinction going to what Theodore Audel called a 'dynamic leverage arrangement'. Most throttles are as shown below- pinned in 3 locations along a bell crank that translates the pull back motion of the throttle yoke to the raising/lowering of the throttle plug. (The image below is a representation of a K-36 throttle valve to be precise- taken from theironhorse.blogspot.com- all credit to them).



This is an example of a 'First class' lever, or one whereupon a force is applied opposite a fixed pivot point to produce the desired output (See diagram below- also not mine).



The K-37s bell cranks/throttle bodies are arranged a bit differently. When beginning to open the throttle, it acts like normal- a First class lever (albeit with a very small advantage, though we'll get to that). The main difference in form is that the pivot pin is not held in a constant position, only resting at the bottom of a vertical slot. When the bell crank has rotated far enough, two 'ears' on the far end of it make contact with 2 bosses cast into the throttle body itself- keeping the crank from pivoting further (In the drawing below, when 'ear' A contacts boss B ). From this point, the pivot becomes the contact area between A and B, changing the linkage to a Second class lever. This allows for two things- a greater lift from when A has hit B and beyond, as well as finer control of the otherwise massive throttle plug before that- in theory great for switching or drifting maneuvers.



Now, this is all fine and dandy in theory, though has some trouble in practice. While the first class stage is great for light movements on level track, at tonnage (I say like we've ever even had 491 close to tonnage at the museum ) it doesn't grant enough 'umph' to really do anything, and winds up feeling like a lot of dead space on the quadrant. When you finally get far enough out to do anything, you're right on the threshold of A touching B, which as discussed, will alter the leverage arrangement. Combined with the lack of smooth translation within the crank slot, the effect is as follows: A whole lot of nothing, a hard spot that the throttle doesn't seem to want to open past, and suddenly waaaaaaaay too much power- usually accompanied by a whole lot of slipping.

This is all atop the fact that the throttle body itself is essentially a 10lb load in a 5lb bag- it barely fits in the dome. The K-37 throttle bodies are all one piece- not 2 like most engines (stand pipe + plug capture). To finagle that thing in and out usually takes between 4-5 hours of solid lifting, rotating, and bumping around. We're still not sure if this was a Baldwin idea dating back to the C-41's, or some bright idea by the folks at Burnham, but one thing's for sure- it's a pain and a half to deal with.

I'm sure I've missed something character here- Dusty? Jeff? Mark? Anything to add? Perhaps Charlie or Randy as well, considering it was them that brought up the dynamic leverage thing.

Cheers!
- Brett



Edited 1 time(s). Last edit at 02/15/2019 01:43PM by Brett Wiebold.