Modifications for 4-3/4" Gauge from 5" Gauge
Only a few things must be done the re-gauge this locomotive from 5" to 4-3/4". The first obvious parts to modify, are the frame spreaders. These are the pieces that set the distance of the two main frame pieces. After checking wheel and track standards for U.S. 4-3/4" gauge track, I discovered that is was simply a matter of making the frame spreaders exactly 1/4" narrower than the drawing.
One of the other main things to change was the width of the bottom of the fire box. Because of this, I had to plan exactly how the formers for the boiler plates were to be made, to maintain the gap between the outer sides of the fire box and the frames. The sides of the fire box should not touch the frames. This will cause the frames to "steal" heat from the fire box unnecessarily. Heating up parts other than the boiler and fire box will be wasted energy and cause inefficiency. With such a small grate, the attempt is to make everything as efficient as possible.
The smoke box saddle casting must be also modified to fit between the frames. When this is done, the area of the casting that meets the frame sides is machined away completely. So, a new piece must be fabricated to replace the removed area.
The axles must also be shortened by 1/4". The critical dimension is the shoulder to shoulder distance that the wheels fit up next to. This will set the gauge of the locomotive.
I left everything from the running boards up, pretty much as per the drawings. Also the front and rear beam were left as per the drawing. Where the frames are attached the beams, thisis what was changed. Each frame was attached to the beams, 1/8" farther toward the center than as drawn.