George Andrews Wrote:
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> Tom, your knowledge of steam power is unsurpassed;
> thank you. You mention low gearing on the Shay;
> was this done strictly through the "ring & pinion
> " gears on the wheels & side shafts ??? Did the
> crankshaft offsets at the connecting rods also
> play into the different gearing ??? Sorry for the
> automotive terms; I don't know what else to call
> them. Also, on a rod engine, did a smaller driver
> diameter equate into a shorter piston stroke ???

George, thanks for the kind words, but like most of us, I still find myself in error at
times and there's plenty that I don't know. I just happen to have always been interested
in steam locomotive specs and the differences between them. It also helps that I worked
in large boiler houses and operated machinery all my life.
Lima designed the Pacific Coast type Shay with modest sized 13 by 15 inch cylinders, only
one inch bigger in diameter than a 70-3 type. These cylinders are half inch smaller than
standard gearing on an 80-3 Shay, but the PC has more power. How does it do that?
Boiler pressure is the same at 200 lbs. Driver size is the same at 36", so the only other
part of the formula that comes into play is gear ratio. Standard gearing on 80-3 and 90-3
Shays is 20 to 41 (20 on the pinion and 41 on the ring) giving a ratio of 2.05 to one.
The Pacific Coast type had 3 less teeth on the pinion, 17 and the same 41 on the ring giving
a ratio of about 2.41 to 1. Did I get the math right on this last one? Anyway, you can see
the difference and it was all done with the teeth. You could feel the difference on just
those 3 teeth when you ran the 11, I still remember it and can compare it to the times that
I rode Sierra's 2, a 90-3 class Shay with the 2.05 to 1 gearing. PC Shays were a fine
machine, don't get me wrong, but there was a mechanical compromise in their design.
You also asked about rod engines having smaller diameter drivers and did it equate with
a shorter piston stroke. To a degree, it did. But it was also determined on just where the
crankpin was located on the main driver.
Hope this was of a little help. BTW, anybody ever wonder why Lima went with 41 teeth on the
ring gear and not 40, making it an even 2 to 1 gearing? An old machinist told me that the
one odd tooth was called a "hunting" tooth and meant that on each revolution that the teeth
would come in contact with different teeth than on the previous turn. This was somebody's
thought to even up the wear on the teeth. Pickering's bigger Heislers, the 1 and 5, had
straight 2 to 1 gearing, 12 to 24 teeth. That and 40 drivers made them faster over the road
and that's why they were preferred for many years taking the empties from Fassler (Standard)
out to Schoettgen Pass at Mile 28. They could make much better time than the Shays and still
haul sufficient tonnage up the hill.