The last time I was out at the Il Railway Museum, I spent some time taking a close look at the ATSF Northern they have and noticed that it has 2 side-rods on each side between the 2nd & 3rd drivers. Were these engines built that way or was this a modification done to prevent breakage???
I looked at some pictures, but couldn’t see what you described. It might be something added by the museum. Do you have a picture you could post?
See you around the forums,
Daniel
The type of rods you describe are known as “Woodard Rods”, having been patented by an engineer of that name at ALCo in the 1920s. It reduced the stress in the connecting rod crank pin by putting a coupling rod outside the connecting rod as well as inside and reducting the bending stress in the crank pin.
Which ATSF Northern were you looking at? The 3750 class were heavily rebuilt and might have got these rods subsequent to building, but the 3760 and 2900 classes probably had them from new.
Peter
This was on ATSF 2903 which used to be at the Museum of Science and Industry but has been moved to the Illinois Railway Museum. Here’s a link with some pictures of the move, but you can’t really see the double rod in the second pic. I don’t have any good pictures of it but it is as you described it. If I remember right, SF liked to run pretty high steam pressure in their engines, so reducing crankpin stress would make sense.
And as long as we are on this subject the four classes of Santa Fe Northerns and quantities are: 3751 class-14, 3765 class-11, 3776 class-10, and 2900 class-30. All those Northerns add up to 65 total.
All 2900 class Northerns had steel alloy rods (friction bearing type) when they were built in Baldwin in 1944. All steel rods were replaced by the light weight roller bearing rods in the late 1940’s. The double rods were placed between axles 2 and 3 which “locked in” the main rod and the side rod between axles 3 and 4. This design distributed the rod thrust over the length of the main driver pin (axle 2) and the number 3 axle pin. This particular rod arrangement was utilized on all four axle reciprocating steam locomotives with one exception -(that I know of) - the Norfolk & Western “J” class.
I haven’t seen nearly as many as I’d like, but the Northerns with modern running gear that I’ve seen usually have a single 2-3 side rod which is forked at the ends. The 1-2 & 3-4 rods fit between the jaws. All the Northerns at IRM are like that(Milw, GTW) and I know UP 844 is that way so I would suspect other late model Alco’s would use that design(NYC, RI).
Guys,
Sorry about my oversimplified reference to the Santa Fe Northern classes. I think that the forked end rod may also be a Woodard patent (hence its use on Alco locomotives). The dual rod might be a version used with roller bearings, which of course the 2900 class had.
Peter
I’m just a bit astounded at these references to “Woodard” rods being related to Alco in the '20s. These are a classic feature of Super-Power, and were developed by a fellow by the name of W.E.Woodard… but his Alco days were almost certainly behind him at the time, and attribution to Lima would be much more appropriate…
There is a difference between a fork-and-blade rod on a common driving pin or crank journal (as used on EMD 567s. for example) and a tandem rod. Both have the same effect, but implementing the fork-and-blade end on a lightweight roller rod would involve far too much mass and stress raising fillets compared to the alternative of two fairly light rods side by side. Remember that the overall bearing diameter used in these rods could be substantial, and would be greater still if a spherical bearing needed to be provided to allow lateral motion. It is not difficult to imagine what would be involved with center-to-center distances needed to put a roller in a fork-and-blade articulated rod configuration!
In both fork-and-blade and tandem configurations, the idea was to keep the line of thrust through the rodwork in as much of a continuous line as possible; a single rod would either have to be articulated (which involves an extension of one rod past its crankpin to form a knuckle for the following rod, cf. the UP 4-12-2s for an example of this construction) or would involve taking the main-rod thrust further outboard (for various reasons you wouldn’t want all the siderods stroking outside the throw of the main rod!) hence requiring a heavier main crankpin and increasing the problems with cross-balancing the engine (etc.) I have seen discussion that tandem conventional rods were necessary on some engines to allow ‘higher loading’, but I suspect this involves bearing lubrication more than any additional cross-section of metal in the rods per se.
I can’t think offhand of locomotives using more than one set of tandems, for the rod connection from the main dri