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Working/Shifting Valve Gear<br />
Tom Mix, Capt., USMC Ret.<br />
Sometime in the 1970s, an O <strong>Scale</strong> builder wrote an article<br />
in Model Railroader about his scratchbuilt steam engine<br />
for which he made a simple method to shift the valve gear<br />
into the proper position for forward and reverse travel of the<br />
engine. He made the statement: “It has always bothered me<br />
to see an engine moving in reverse when the valve gear was<br />
set for forward travel.” While constructing a Burlington 2-10-<br />
4, I remembered that article but could only recall the basic<br />
setup, so I did some experimenting with the method this<br />
author used.<br />
Photo 1 shows an assembly made up using a 2-56 screw<br />
as the method to move a pin back and forth when the main<br />
drive motor is set to forward or reverse. This pin had a rod<br />
connection that went forward to the loco reverse shaft. I had<br />
built the Baker valve gear assembly from both scratchbuilt<br />
and commercial parts to properly function. I couldn’t see<br />
how Baker valve gear really worked until I made this shifting<br />
unit to move the reverse shaft back and forth and then the<br />
light went off… “Dang! That’s how it’s done!”<br />
This unit is set up in a fixed position between the main<br />
drive motor and the axle gearbox. As power is fed, the<br />
motor begins to turn but the loco is stationary until the<br />
threaded pin assembly slowly reaches the stop point; then<br />
the engine begins to move with the valve gear properly<br />
positioned. From the photo I hope you can see the principle<br />
of this action. In the photo the pin is positioned at the midpoint.<br />
The assembly is 1-3⁄4” long and 1⁄2” high. Worked<br />
like a charm, in one direction only.<br />
Going forward was okay but when stopping the engine,<br />
then setting the power to reverse, the engine would directly<br />
move in that direction without resetting the valve gear<br />
because the shifter pin assembly wouldn’t release right<br />
away. But it would release as the engine was moving which<br />
caused the loco to suddenly stop, the valve gear changed<br />
position, then it took off again. This was not prototypical.<br />
But stopping the engine, and setting the power for the forward<br />
direction, that shifter moved the valve gear into the<br />
correct position and it would move off. That was prototype.<br />
I tried using a lubricant where the two contact points met<br />
the threaded pin assembly but operation was sporadic;<br />
sometimes it moved properly and sometimes it didn’t. I put<br />
July/Aug ’08 - O <strong>Scale</strong> <strong>Trains</strong> • 17
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