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I was given a Pentrex , Cumbres & Toltec cab ride VHS tape (remember VHS??  ).  The commentator mentioned that the engine being an outside frame configuration (driving rods connected to counterweights whose axles extended to wheels inside the frames), delivered more power than a normal inside frame configuration (driving rods directly connected to wheels outside frame) would.

http://cs.trains.com/mrr/f/11/t/66176.aspx

Wondered if this was true statement.  Assuming engine weight, cylinder size and steam pressures etc. could be made equal between inside and outside frames, wouldn't the available drawbar pounds be about same?  I realize the C&T is smaller narrow gauge compared to standard gauge engines, so wonder how this was true, or basis for this statement.

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Brian Solomon in his book Steam Locomotives (page 109 -- "Narrow Gauge Locomotives") says that prior to 1900 most narrow gauge engines were just smaller versions of standard gauge machines, and were built with the same arrangement of inside frames. The narrow inside frames, however, limited the size of the firebox and thus the power of the engine. Starting in 1903 D&RGW solved this problem by fitting outside frames to their new Mikados, which allowed the use of a larger firebox supported by a trailing truck. The larger firebox made these engines more powerful than an equivalent locomotive fitted with narrow frames and a smaller firebox. 

Here's some additional information from Guide to North American Steam Locomotives (pages 158-159): " The difficulty of scaling down a standard gauge locomotive was that the power output was similarly scaled down, and the most severe limitation was firebox size. A firebox between the frames of a narrow gauge engine couldn't be much wider than a coal shovel; placing a firebox above the frames helped, but it was still limited by the back-to-back spacing of the wheels. Moreover, space between the frames was too restricted for easy maintenance of journals and valve gear."   .....   "By 1903 locomotive technology had progressed so that Baldwin could build 2-8-2s for D&RG with twice the pulling power of the Consolidations. The locomotives were Vauclain compounds, and they had outside frames. The trailing truck supported a wide firebox entirely behind the drivers, and the wider spacing of the frame rails made the locomotive more stable than an inside-frame model."

So outside frames offered a variety of advantages. But accommodating a wider firebox was still the basic reason for adopting outside frames.

wjstix posted:

IIRC, didn't the D&RGW have some engines that were original built as standard gauge, but were converted to 3' gauge by making them outside frame engines?

Thoses are the K-37 class 2-8-2's.  They started life as standard gauge C-41 2-8-0's, and were rebuilt in the Burnham shops using new frames.  The original tenders were reused, and the wheels on the tender trucks were regauged by moving the wheels inboard on their axles.

Stuart

 

Last edited by Stuart

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