S.P Cab Forward modifications

[UP 829]

Besides obvious changes like fuel and water lines, rebuilding the cabs, adding a 4 wheel pilot truck etc., where other less obvious changes needed for them to run cab first? Examples might be changes to springing, lateral motion, or centering devices. Did running them backwards stress the frames in unexpected ways? Also most roundhouses were set up to take locos smokebox first, did S.P. have to change servicing facilities for these locos?

[Lost World]

You do have to wonder what kind of problems running the valve motion "backwards" might have caused.  The PRR had problems with the rear engine of Q-1 duplex, which ran in reverse all the time.  Whatever problems the SP might have had must not have been major, however; unlike the Q-1's the cab forwards were highly succesful.

[GP40-2]

Cab Forwards were just reverse running Yellowstones (2-8-8-4s). Their pilot truck was the same as a Yellowstones trailing truck. The PRR rear engine problem resulted from ash contamination from the firebox, not from backwards valve motion.

[Lost World]

Cab Forwards were just reverse running Yellowstones (2-8-8-4s). Their pilot truck was the same as a Yellowstones trailing truck. The PRR rear engine problem resulted from ash contamination from the firebox, not from backwards valve motion.

My bust; should have remembered that.

[UP 829]

Cab Forwards were just reverse running Yellowstones (2-8-8-4s). Their pilot truck was the same as a Yellowstones trailing truck. The PRR rear engine problem resulted from ash contamination from the firebox, not from backwards valve motion.

The early versions were 2-8-8-2's and 4-6-6-2's. The 4-6-6-2's had a inside frame 4 wheel pilot truck similar in appearance to what was commonly used on Pacifics, Mountains, etc. and I'm guessing the same type of centering mechanism??? The later 4-8-8-2's have an outside frame pilot truck that looks much lighter and different from any 4 wheel trailing truck that comes to mind, a GS-1 for example, but again I don't know what type of centering was used?

[MopacBarrettTunnel]

Cab Forwards were just reverse running Yellowstones (2-8-8-4s). Their pilot truck was the same as a Yellowstones trailing truck. The PRR rear engine problem resulted from ash contamination from the firebox, not from backwards valve motion.

The early versions were 2-8-8-2's and 4-6-6-2's. The 4-6-6-2's had a inside frame 4 wheel pilot truck similar in appearance to what was commonly used on Pacifics, Mountains, etc. and I'm guessing the same type of centering mechanism??? The later 4-8-8-2's have an outside frame pilot truck that looks much lighter and different from any 4 wheel trailing truck that comes to mind, a GS-1 for example, but again I don't know what type of centering was used?

 

First of all, some basic cab-forward information can be found at

http://www.steamlocomotives.com/cabforward 

As for the lead truck centering-device question, as far as I can tell, the SP's cab-aheads had no "special" fittings other than what worked well under a "normal" {cab in the rear} steam design.  It's also interesting to note that the "pilot" trucks on the AC4-12's closely resembled what eventually became the AAR-type A "switcher" truck during the diesel era.  Was GSC thinking "ahead of the curve," or did they simply refine an already practical design for the diesel application?