WP & D&H 4-6-6-4 steam locomotives - Trains Magazine

The D&H J-95 class 4-6-6-4 looks to have been a “refined” version of the original UP design.  Most of the basic dimensions were the same.  It had cast frames and a single-plane articulated joint (*), whereas the UP original had bar frames and a modified two-plane articulated joint, the modification being the addition of a friction damping mechanism for the pitch axis.  Nominal axle loading was higher, at 68 000 lb as compared with 65 000 lb.  And the front driver set had a slightly greater static loading than the rear set, to offset weight transfer on upgrades.  The front engine steam pipes conformed to the later Alco jack-knife-with-ball joints pattern.  (Perhaps the J-95 was the first application?

The higher steam pressure, 285 lbf/in² as compared with 255 lbf/in², did not fully offset the reduced cylinder diameter, 20.5 in as compared with 22 in.  (The net tractive effort ratio was 0.97.)  Given that the J-95 had a higher adhesive weight (406 500 lb) than the UP CSA-1 (386 000 lb), it looks as if D&H was concerned about the apparent potential slipperiness of 4-6-6-4 locomotives.  (Although a factor of adhesion of 4 was probably fine for x-8-8-y articulateds, something higher, maybe towards 4.5, was evidently preferable for the x-6-6-y type.)

The single-plane articulation joint necessitated that the front engine be equalized as a single unit, rather than in two sections, but otherwise the springing was similar, as were the lateral controls, which were one lateral motion device per engine unit short of the “full works” Alco/Blunt lever system.  (Maybe the later D&H builds were “full works”, as that was used on the 1943 D&H K-62 4-8-4.)

Both the “Railway Age” 1940 August 10 and :Railway Mechanical Engineer” 1940 September articles on the J-95 note that the crossheads were of the Laird types, arranged with the Becker design of wrist pin, removable from the outside.  The Becker device was covered in US patent 1599740 of 1926 September 14, filed 1924 September 30.

The WP M-100 class 4-6-6-4 might have been simply a somewhat heavier version of the UP CSA-1, although I haven’t seen a detailed technical treatment of it in the literature.  Adhesive weight was 416 000 lb, for an average axle loading of 69 500 lb.  The 265 lbf/in² boiler pressure slightly more than offset the 70 inch drivers, the net tractive effort ratio as compared with the CSA-1 being 1.02, against an adhesive weight ratio of 1.08.

Regarding the WP’s stillborn interest in 4-8-8-4 locomotives, there seem to be two versions of this story.  Virgil Staff, in his book “D-Day on the Western Pacific”, notes that in 1941 February the purchase of 10 such locomotives was contemplated for service over Wendover Hill, displacing the M-100 class 4-6-6-4s from that section.  It was said “Contacts were immediately made with the Union Pacific, and WP considered having its own order attached to that of the UP power then under construction.”  However, the WP had second thoughts, and instead opted for the EMD FT.  The book chapter in which this was recorded was “Knuckle Busters or Big Boys!”.  A WP variant might have been slightly heavier, as WP appeared to work to a 69 000 lb nominal axle loading, as compared with 67 500 lb for the UP.

Staff appears to have been quite meticulous with his research for the book, so what he said is more likely to have been gleaned from the WP records than inferred by him from less definite information.  But that said, it is possible that both stories are applicable.  As well as considering the UP design, WP might also have had a dialogue with Baldwin about a 4-8-8-4 derivative of its M-137-151 class 2-8-8-2.  (The DM&IR 2-8-8-4 of 1941 was also said to have been a derivative of the WP locomotive.)

(*)        The J-95 was, as far as I know, Alco’s first application of the single-plane articulated joint.  N&W had used it in 1936, on it’s a class 2-6-6-4.  After Alco, Lima used it on the 1941 C&O 2-6-6-6.  Baldwin was late though, with first use on the B&O EM-1 class 2-8-8-4 of 1944.  But then, somewhat surprisingly, it also used it on the final batch (1949?) of the C&O 2-6-6-2 Mallet, in conjunction with bar frames.  I recall seeing that type of locomotive at the Baltimore museum (in the late 1980s I think), and being very surprised when I had a close look at the running gear.

Cheers,