Earl Wrote:
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> It is not possible to properly balance a small
> drivered (less than 50" locomotive) There isn't
> enough space on the driver to put enough
> counterweight in there. Therefore a 44' drivered
> locomotive is not going to be properly counter-
> balanced for "high" speed.
Is there a counterweight on the crank of the main axle of the K-28's for this reason? And on all cranks of the newer engines?
> The other factor to look at is piston thrust. You
> can counterbalance for the rods or thrust, but not
> both. Piston thrust makes the engine "hunt" from
> side to side. Engines built for high speed tend
> to be counter-weighted for speed and fairly rigid
> lead truck keeps them pointed straight ahead.
> This is how the N&W could get their J's with 70"
> drivers to run 90 mph and the SP and ATSF could
> get their 4-8-4's run well over 100 mph.
The older ATSF 4-8-4s were rebuilt with one-piece cast steel frames, and the newer ATSF 4-8-4s and all the Daylights (and I presume the N&W Js) all had one-piece frames as well. Two of the Daylights and all of the other 4-8-4s mentioned here (plus U.P.'s) had roller bearings on all axles. All of this taken together results in much less wobble due to piston thrust, and is a big factor in their high-speed capabilities.
>
The 470's were able to run close to 50.
That's what I thought too, as noted above.
> I know guys who have been on them at 45 regularly.
> The scheduled passenger speed on the dual gauge south
> of Alamosa was about 35mph. 480's and 490's would
> start to hunt badly at 35 because the piston
> thrust would overcome the centering device on the
> pilot truck ...
... and the slight wobble due to built-up frames and slack in the bearings, etc., etc.
Thanks, Earl!!
- Russo
Edited 1 time(s). Last edit at 12/03/2009 09:43PM by Russo Loco.
