611 Rods

Wed May 6 20:32:58 EDT 2015

I’m not certain what generated this conversation, but it was timely.  In the past two months, as more and more disassembly shots of 611 have become public, I found myself wondering why the tandem rods (which I’ve also seen referred to as “extended main rods”) were dispensed with.  

My understanding for the adoption of extended or forked big end main rods was to allow spreading the thrust of the main rod over a larger area, and perhaps buttress any deflection of the main driver pin.  I’d read somewhere in the past that 4-8-4’s were beginning to find the limits of crankpin strength, so the tandem rods seemed to fit this problem well.  The assumption on part is that the main pin was the problem area.  I’d also wondered if the attendant very long fourth axle crankpin was ever a problem - it’s a long lever!  This conversation below seems to say “yes”.  It also answers the “why” as to the dispensing.

It would seem that the conversion would have been pretty straightforward - shortening the main, third and fourth axle crankpins and rebalancing the main and third drivers?  Is that correct?  Would the (now) inboard connecting rod between 3 & 4 require any change to balance to offset the (presumably) lower rocking couple?  Was the connecting rod between 2 and three any beefier than the tandem rod that it replaced?  Or did the inner rod have enough strength to leave it “as is”?

Matt Goodman
Columbus, OH

On May 4, 2015, at 8:33 AM, NW Mailing List <nw-mailing-list at nwhs.org> wrote:

The rods for all Js (and other N&W Shop-built engines) were made in Roanoke Shop.  Replacement rods for older N&W power were also made in Roanoke.

Lightweight rods for the Js and last five As were made from an alloy furnished by Timken known as "high dynamic" alloy.

They were all forged in Roanoke's Smith Shop and machined in the Machine Shop.  The web on the side rods of the J was a quarter inch thick.  The web on the J main rods was a half inch thick.

Roanoke didn't need anybody's help in manufacturing side or main rods, or any valve gear parts not furnished by the Pilliod Company (the Baker mechanisms).

Roanoke also made side rods for the Gainesville Midland 2-10-0 #206, which you can see today in Spencer Shops as Seaboard #544.  Roanoke made two side rods for the Russian Decapod to replace two broken in service.  They're easy to spot on the preserved engine.

Ed King

-----Original Message----- From: NW Mailing List
Sent: Sunday, May 03, 2015 11:10 PM
To: NW Mailing List
Subject: 611 Rods

I'd like to clear up some questions regarding the side rods on the 611.

Some people have claimed that the rods for the 611 were fabricated in
the shops in Roanoke, referring to an N&W film that shows rods being
forged and machined in Roanoke Shops.
Others stated that the rods for 611 were made by Timken, not the N&W's
Roanoke Shops.

So here's the story:
The rods for the Class J were originally fabricated in Roanoke Shops as
shown in the company film. Look closely and you will see that the
intermediate rod between the number 2 and 3 drivers was actually 2 rods
installed side-by-side. This caused the rods to be set out from the
drivers and the need for long crank pins.

According to Bud Jeffries' book "Giants of Steam", in 1952 a failure of
the crank pin on the number 4 driver led to a redesign of the rods. The
new lightweight rods only required one rod between the drivers, allowing
the rods to be located closer to the wheels and shortening the
crank-pins. This reduced the stresses seen by the crank pins and solved
the problem.

These new rods were fabricated from a lightweight alloy by Timken, not
Roanoke Shops. The new rods were installed on numbers 600, 605, 610 and 611.

So despite the N&W film showing rods being fabricated in Roanoke, the
rods on 611 today were made by Timken.

Ron Davis

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