Re: New Broadway Limited UP 4-12-2

Tony Thompson

Arved Grass wrote:


Marty (last name?) had his O-scale 4-12-2s on display at Cocoa beach. He was especially proud (rightfully so) of his model with the triple Walshearts valve gear. I noticed the timing issue as well, and asked him about it . . .

      Arved, the whole point of three-cylinder power was to provide three piston thrusts per driver revolution, rather than just two, evening out the loading on the entire running gear. Obviously these thrusts were made to be as close as possible to being equally spaced. But arrangements like the Gresley, with an inclined cylinder, the angle of inclination of the crank had be added to one side and subtracted from the other, to get equally spaced thrusts in time. This was not necessary with the triple Walschaerts gear, and cranks on those engines were indeed at 120 degrees. Bot Church explains this very clearly in his book.

Tony Thompson             Editor, Signature Press, Berkeley, CA
2906 Forest Ave., Berkeley, CA 94705
(510) 540-6538; fax, (510) 540-1937; e-mail, tony@...
Publishers of books on railroad history

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