Stuart posted:There's been all sorts of debates of the two "single guide crosshead designs, Laird and Multiple Bearing, versus the double guide "Alligator" design. As the OP noted N&W used the multiple bearing design on the first five J's (600-604), plus the first ten class A's (1200-1209). For the rest of those two classes they went to the Alligator design. I believe that they found the Alligator design to either be easier to adjust, or more rugged (or maybe both).
Meanwhile on the New York Central, the class L-4a Mohawks had Alligator, while the L-4b class has multiple bearing crossheads.
On the Southern Pacific, all of their modern power used multiple bearing crossheads, except the Cab Forwards, because with the reverse running of the drives, the mainrod would exert greater force on the lower crosshead guide of the Alligator crosshead, while using a multiple bearing crosshead would have had more problems because of that same issue.
Stuart
Thank you for your response. Just for clarification, are Laird and MB the same? I’m guessing the name “Multiple Bearing” refers to the fact that a single support guide must be strong enough to endure thrust from multiple directions. Is reduced friction even a consideration?
