today, I have a tuning report of my Accucraft Shay. No, I didn’t spend a low-rider chassis neither a V8 motor… But I could improve the running of the loco very well.
Large scale railroader Bill Allen wrote an article regarding the Porter-style “Ruby” made by Accucraft. After measuring and calculating, he determined, that the steam port holes in the valve chest are to small comparing the piston valves. He figured out, that a wider steam port will negotiate and improve the running characteristic of the Ruby in both directions. You’ll find all the details in the following PDF.
Since the Shay uses the nearly the same parts for the steam engine, Bill Allen’s method might work here as well. I dismantled nearly the whole loco to get the steam engine apart and drilled the steam ports to 1.9mm. Unfortunately, I’ve no photos of this step.
Once the loco was re-assembled, I made a first test-run and as expected, the stalling in reverse was mostly gone. The remaining stalling comes from worn out eccentrics. To solve this issue as well, I added ball bearings 10*15*4mm with flange. I used the original eccentric and valve rods, which I machined to snug fit on the lathe. The last step was some fine-tuning on air, to adjust the valve-timing.
Here’s a short video, showing the loco during several test-runs.