PRR 5841 posted: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?
The Laird and multi bearing crossheads are two different designs. Santa Fe made the Laird on many of their modern designs, such as the 3751 class 4-8-4 (Santa Fe 3751 Laird crosshead). As you can see in the picture the Laird crosshead guide has two horizontal bars with a slot for the crosshead to hang out of the side.
The multiple bearing (MB) crosshead was used by many railroads, such as Union Pacific on their modern designs, such as the FEF-3 (844) (Multiple bearing crosshead on UP #844). On the MB crosshead guide the slot was beneath the guide, with the crosshead hanging below it.
I hope this was helpful.
Stuart
