• B&M R1 Mountain

  • Discussion of steam locomotives from all manufacturers and railroads
Discussion of steam locomotives from all manufacturers and railroads

Moderators: slide rules, Typewriters

  by Engineer Spike
I have some questions about the B&M R1 class. I’ve read in many places that a 4-8-4 design was really desired. The Mountains were a compromise. The material that I have read states that the company was avoiding another bridge strengthening project, which they had previously done to run the T1 class 2-8-4 Limas. This has given me some questioning of the fact that upgrading bridges would have been necessary.

First, the R1 class was about the largest Mountain ever built. I’m sure that they were very close, if not heavier than some Northerns. Having an extra axle would have surely spread out some of the weight. I don’t know if extra length would have been required, and thus negating the weight that the extra trailing axle would have handled.

Furthermore, I do know that steamers have a more concentrated load. Who also knows what upgrades the bridges have had over the years. Knowing that B&M was never rich, apparently many of the same bridges carry 263, and some 286k tonnages now. I guess that my question is whether the modern jumbo equipment still comes anywhere close to putting the same concentrated loads? Were the engineers being overly cautious about the bridge loadings?

It makes me curious if a smaller Northern would have had the same characteristics in both freight and passenger service. Large fireboxes with four wheel trailing trucks seem to be the crux of Lima’s Super Power design. This makes me really wonder whether a Mountain was really a step backwards from the previous T1. This comparison may be apples to oranges because the T1 was low drivered freight power, while the R1 was dual service.

I’d like to have your thoughts. Maybe this whole issue is based on rail buff lore.
  by Pneudyne
The "story" in railfan literature about bridge loading limitations outruling a 4-8-4 is one of those that might have a single source. It may be worth checking the Railway Mechanical Engineer (1935 October) and Railway Age (1935 August 17) articles, if they can be found.

A “light” 4-8-4, such as the NC&StL design, would probably have fitted within the total weight limitation that applied, but might have been short on adhesive weight against what B&M saw as desirable for the envisage duties. It is reasonable to assume that B&M wanted driving axle loadings at the maximum allowable, say 67 500 lb given that the R-1 had an adhesive weight of roundly 270 000 lb. The NC&StL 4-8-4 (derived from the USRA 4-8-2A) had an adhesive weight of around 220 000 lb.

If total weight was the limiting factor, then to a first approximation, the R-1 is probably where you’d arrive if you started at say the Rock Island R-67B 4-8-4 (which could accommodate 73/74 inch drivers even though built with 69 inch) and downsized the boiler enough to get it on a 4-8-2 chassis at the same adhesive weight. The Rock Island R-67B had a grate area of 88 ft² and a BMOD of 98 inches, whereas the B&M R-1 had 79 ft² and 96 inches.

Although that said, one may note that the MoPac 1927 4-8-2, which was probably a precursor to the R-67B, and whose lineage can be traced back to the USRA 4-8-2B, had 84 ft² and 98 inch BMOD. Probably though a modernized version of this would have been above the weight limit, whatever that was.

Perhaps the B&M could have considered a 69/70 inch drivered 2-8-4, such as the Van Sweringen (NKP) design, which as initially built was similar in weight to the R-1. It had 90 ft² grate area and 98 inch BMOD. Adhesive weight was probably less than the B&M desired, but later iterations of that 2-8-4 design had much higher adhesive weights, so building it to 270 000 lb on drivers should not have been a problem. But this kind of locomotive might have been of lower utility to the B&M. At a given level of track stress, and with comfortable riding, the R-1 could probably run quite a bit faster, this due to its higher diameter drivers and its four-wheel leading truck. It was evidently fast enough for some passenger services. Whilst the 2-8-4 might have been able to go as fast, its top allowable speed in regular service was probably determined by tracking and riding considerations deriving from its 2-wheel leading truck. And those limitations made it not worth going above 69/70 inch drivers. One may wonder if the Van Sweringen 2-8-4 had more power than it could fully use in typical service.

With a large 4-8-2 such as the B&M R-1, the wheel arrangement may have dictated a lesser firebox size than would be considered ideal, in turn resulting in specific combustion rates at the high end of the acceptable range. Evidently that was an acceptable engineering tradeoff considering the constraints and the intended duties.

The B&M, as a user of the much-hyped original Lima 2-8-4 design, was not alone in not further developing this wheel arrangement.

Of some of the others, the IC also turned to the 4-8-2. One could argue that this was in part an exercise in convenience, as it rebuilt some of its 2-10-2 fleet as 4-8-2s (with 88 ft² grate area). But it then perpetuated the 4-8-2 with new designs. In its 1930s rebuilding programme, whereas the 2-8-2s were central to it, its 2-8-4s presented a conundrum, with one unsuccessful rebuild to a 4-6-4 before updating in kind was settled upon.

B&A’s use of the original 2-8-4 appeared to have had no influence on parent NYC, who instead elected to progressively develop the 4-8-2 for fast freight.

MoPac moved from the 2-8-4 to the 4-8-4 for fast freight, and rebuilt its 2-8-4s as 4-8-4s. Interestingly, its 2-8-4s had had an 88 ft² grate area rather than the original 100 ft², suggesting that Lima had in the first place gone “over the top” with this parameter. (The 90 ft² grate area of the Van Sweringen 2-8-4 also points to this.)

Perhaps it could be said that the original 63-inch 2-8-4 probably had more power than it knew what to do with.

At a given adhesive weight, as intermediate between say a 63-inch driver heavy 2-8-2 and a 73/74-inch 4-8-4 one could have either a 2-8-4 or a 4-8-2. Both solutions were chosen, and it would be difficult to say that one or the other predominated. Rather individual railroads chose that which best fitted their specific requirements. The simplistic conventional wisdom might have been that the 2-8-4 must have been better because it had a four-wheel trailing truck, which in turn allowed a much bigger grate area and was also one of the key elements of the “super-power” type, to which august group the 4-8-2 was denied entry because it had only a two-wheel trailing truck. But reality was not quite like that. There was not always such a marked distinction. For example, consider that the original UP 4-6-6-4, generally considered to be in the superpower class, was in some ways an articulated derivative of the 4-12-2, and retained the same 108 ft² grate area. The extra trailing axle was probably required mostly to accommodate the extra weight. The DM&IR 2-8-8-4 was also superpower, but had the same firebox dimensions as the non-superpower WP 2-8-8-2 from which it was derived (and actually a smaller grate area, 125 ft² as a compared with a notional 145 ft²). The extra trailing axle was there to accommodate the weight growth, not a larger firebox. The NKP 4-6-4, as I understand it, was essentially a USRA 4-6-2A with a 4-wheel trailing truck to spread the weight, but with the same grate area,

An interesting feature of the B&M R-1 was that its trailing axle was 12 ft behind the hind driving axle, a bigger distance than was typical for heavy 4-8-2 locomotives. This may have been to get the trailing axle somewhat out of the zone where bending moment augmentation occurred. The high railhead stresses caused by heavily loaded trailing axles of x-y-2 locomotives had been noted in the 1920 AREA proceedings. Trailer axle loading for the R-1 was probably about the same as that for the driving axles. With four-wheel trailing trucks, the typical axle spacings were probably more likely to be in the range that produced bending moment relief. A four-wheel trailing truck could probably have been accommodated under the R-1 firebox, but that would have increased the weight noticeably, and might have required, for example, a slightly smaller boiler in order to get back down to the target maximum weight. Evidently the chosen trade-off point was a two-wheel trailer placed as far back as reasonably possible.

  by Allen Hazen
Oh frabjous day! Calloo! Callay!
Somebody (perhaps operating under the nom de guerre "Centre for Research Libraries") has scanned "Railway Mechanical Engineer" for the years 1916-1948 (establishment of journal? end of separate publication?), and I can consult it through the University of Alberta library.
Image quality ain't great, but legible (though some edge-of-page, "gutter," characters sort of disappear). Unfortunately I don't seem to b able to download pages to the disc of my own computer, so I can't violate copyright by sharing with anybody else. Sniff.

Anyway, having discovered this new resource (the library didn't have it the last time I tried looking for RME a few months ago), I looked up the October 1935 article on the B&M locomotives: five page article, covering both the R-1 Mountains and the P4 Pacifics. Description of design details (the features that seem to have been thought most interesting, and which are illustrated by drawings, were the multiple-ledge crosshead and its guides, and the proportions of smokebox/exhaust nozzle/stack. Nothing about the rationale for the design (for the choice of a 4-8-2 instead of a 4-8-4 or 2-8-4). I've had a few thoughts on that (probably not adding much to what Pneudyne wrote), and I'll try compose a post about that later this evening.

One thing from the article: weights. The R-1 (first series: the B&M got its R-1 Mountains in three or four instalments over about five years, and it would be too much of a miracle to expect if the weights were exactly the same... but I don't think the differences were significant) had a total engine weight of 416,100 pounds: 78,900 on the front truck, 269,400 on the drivers, and 67,800 on the trailing truck. So the weight on the trailing truck axle is actually a tad more than (the average) weight on a driving axle!
In terms of weight, the R-1 is very close, in total, to a Nickel Plate Berkshire: NKP's first series of 2-8-4, delivered a few months before the first R-1 (and described in the November 1934 RME) had a total engine weight of 416,000 pounds. On the other hand, the R-1 had rather more weight on the drivers: NKP 700-714 had only 254,000 pounds on the drivers )though, as Pneudyne remarked, some later Van Seringen Berkshires were heavier: W&LE 1210-1214 had a total engine weight of 445,500 pounds, with 278,000 on the drivers. (Berkshire weights from 1941 "Locomotive Cyclopedia," pp. 141-142.)
  by Allen Hazen
Oh. Same people have also scanned a lot of old "Railway Age," but their coverage of the title has gaps. 1935, with the article about the B&M locomotives, is in the gap. Sniff.
  by Pneudyne
Thanks for that, Allen. So RME does not give the answer we are looking for, namely why was it a 4-8-2.

Frye, in his book “Minuteman Steam – Boston and Maine Steam Locomotives 1911-1958” said:

“The designers at Eddystone came up with the class R 4-8-2. Reportedly the heaviest Mountains ever built in the U.S., they were actually an outdated machine in many respects. Most railroads and builders were opting for the 4-8-4 arrangement, and in fact a brief glance at the R's could even lead the casual observer into believing that they were Northerns.”

He did not elaborate on the “outdatedness”, but implied is the fact that the R was a 4-8-2 rather than a 4-8-4 automatically made it outdated. There is no hint as to what other aspects of the R were also outdated. From what I can find about the R, it was not avant garde but probably somewhere near the median point of American steam locomotive practice at the time, with at least a partial set of modern features, such as a cast bed frame.

Later on the same page of the book, Frye said: “The Mountains proved themselves very capable and reliable power, doing yeoman service during the crush of WW II traffic.”

From that one would reasonably infer that they were well-matched to their assigned tasks in terms of performance and robustness. So, on the basis of the available evidence, the verdict is that the 4-8-2 wheel arrangement was chosen as being the optimum choice for their intended haulage jobs, given the weight and axle-loading constraints that applied, and not because of any backwards-looking on the part of B&M or Baldwin.

This roster diagram shows the individual axle loadings:
B&M R-1a,b,c.gif
The weight on the main drivers was around 2000 lb greater than that on the others. I don’t think that was too unusual. I don’t know for sure, but I suspect that it was done that way in part to offset to the unloading effect of piston thrust. (An apparent extreme case of such differential driver loading was found on the KCS 2-10-4, which would have had a relatively high piston thrust relative to its mean drive axle loading.) The extra static load on the main drivers would also have been offset by bending moment relief. The very heavily loaded trailing axle at least had no dynamic augment.

The B&M R was not the heaviest 4-8-2, though. At least the IC 2600 class and SLSF 4400 class were somewhat heavier.

  by Allen Hazen
Re: "an outdated machine in many respects. Most railroads and builders were opting for the 4-8-4 arrangement"
I think the presupposed principle -- two-wheel trucks good, but four wheel trucks better, to paraphrase Orwell -- is widely accepted among railfans today, but may not reflect the thinking of railroad motive power people in the 1930s and 1940s.

One bit of history that has intrigued me. The Canadian National got 4-8-2 (6000 to 6058, railroad classes U-1a to U-1e) in the period 1923 to 1930. They then (being a "modern" railway!) switched to 4-8-4 (U-2, subclasses up to U-2h: numbers 6100-6189 and 6200-6224) in the years 1927-1944. (Hmmm... a bit of overlap there. Maybe they tried out a sample 4-8-4 before committing big-time?). I think the U-1 and U-2 were similar in weight on drivers and driver diameter. But for their final order of mainline steam, in 1944, they switched back to a 4-8-2, class U-1f, 6060-6079.

Suggesting that at least CN's motive power people didn't thin the 4-8-2 was outdated!

(Sorry, didn't get to my additional post last night. Will try tonight.)
  by Allen Hazen
Back to the question, why was the R-1 a 4-8-2 and not a 4-8-4 or a 2-8-4.
A history of Boston and Maine motive power policy would, obviously, be helpful. I've only found a short paragraph (with, alas, no sources given) that seems relevant. George H. Drury's "Guide to North American Steam Locomotives" (Kalmbach Publishing, 1993) says (p. 56):

"Before B&M bought its 2-8-4s {AH note: delivery started in 1928], Baldwin had proposed a light 4-8-4 of approximately the same size as the USRA light 4-8-2. [AH note: this would have been about the size, I guess, of NC&StL's 1930 4-8-4, which Pneudyne mentioned for comparison. Not the same design, though: NC&StL's engines were from Alco.] Nothing came of that proposal. As the B&M accelerated its freight schedules, though, it was limited by the 63" drivers of the T-1s. [AH note: the T-1 was the B&M Berkshire. Competing B&A was apparently happier with its very similar Berkshires: I think the B&A had steeper grades than the B&M, so maybe they needed something more specialized for climbing hills.] It needed a faster locomotive that could also handle heavy summer-season passenger trains. Baldwin proposed a heavy 4-8-4 in 1931, but B&M didn't want to upgrade its track and bridges again. Baldwin then proposed an efficient 73"-drivered 4-8-2 -- and delivered five of them, class R-1-a, in early 1935. [AH note: This doesn't say when the initial proposal of the R-1 was made: it could have been shortly after B&M's rejection of the heavy 4-8-4 in 1931: because of the Depression, B&M might not have been able to afford any new locomotives between 1931 and 1935.]"

So. The "light" 4-8-4 wouldn't have been able to do the freight work B&M wanted done. The T-1 Berkshires could haul freight trains, but not as fast as B&M (by the 1930s) wanted. The "heavy" 4-8-4 was too heavy.
Suppose you are Baldwin: what can you offer next? Something with the adhesive weight, tractive effort, and (for speed) horsepower of the heavy 4-8-4, but you've got to trim it down to a weight B&M thinks it can live with. Where do you make cuts? Well, reduce the size of the fire-box a bit (79 square feet is nothing to sneeze at: there were fair-sized 4-8-4 with only 90 or so square feet of grate), and... voilà!

Why not trim the other end instead, and offer something like the Nickel Plate Berkshire? A number of thoughts suggest themselves.
(1) B&M wasn't happy with the speeds attainable with their existing Berkshires, so maybe they indicated a strong preference for a 4-wheel pilot truck.
(2) Baldwin would make a Berkshire if a customer asked for it (e.g. Erie's 1928 S-3), but I don't think their heart was really in it: I suspect Baldwin liked 4-8-2 better than they did 2-8-4.
(3) If, as I suggested, B&M's purchase was delayed because of the depression, the NKP Berkshires weren't there to use as a precedent.
(4) There were high-speed Berkshires out there (Erie had 105 in four classes from three builders built between 1927 and 1929), but the Erie's engines might have been too big and heavy for the B&M.
  by Allen Hazen
As to fire-box size...
It seems to me that American railroads didn't think really big fire-boxes were essential on their 1930s and 1940s steam. I mentioned in an earlier post that Canadian National reverted to a 4-8-2 design after building a large number of 4-8-4. Closer to the case in point, early Berkshires -- both the original 63" drivered version sold to B&A and B&M and the Erie's very big fast-freight versions -- had 100 square foot grates, but later Berkshires -- the Van Sweringen (NKP and copies) Berkshires, L&N's somewhat similar M-1, and P&LE's anomalous A-2 -- reduced this to 90 square feet.

Personally, I would have thought very big fire-boxes would have been desirable. My impression is that North American railroads operated their mainline steam at firing rates (amount of coal per unit are of grate per hour) much higher than European railroads. This was wasteful: the draft of these intense fires was enough toilet fragments of coal and send them, unburned, up the stack! Larger grates would have permitted thinner fires, which would have been more fuel-efficient. (Supporting evidence for that claim: in front of the fire-box, the original 63" drivered Lima Berkshire was comparable to a heavy 2-8-2. In operation, the 2-8-4 could pull more freight, or pull it faster, or ... do the same work for lots less fuel!)

I guess the thinking of American railroad motive power people was that the trade off -- improve fuel efficiency by building much bigger an heavier locomotives -- wasn't worth it. The manager of a railroad in a country with less or more expensive coal might have thought otherwise.

Lima's people seem to have thought bigger fire-boxes were desirable. They propagandized for the four-wheel trailing truck from the 1920s on, and were happy to go to a six-wheel truck (on C&O's H-8 2-6-6-6) and also on some unbuilt proposals. After WW II they tried for some time to interest railroads in a 4-8-6 design: front two-thirds of a freight 4-8-4, but with a firebox like that on the H-8! But by that time most railroad management was interested in locomotives that burned ... even less coal.
  by Allen Hazen
[email protected]#$%^&* autocorrect! In second paragraph, for "toilet" read "to lift".
  by Pneudyne
I think in the CN case the rationale for the late reversion to the 4-8-2 type was that it was more economical for passenger train haulage than the 4-8-4. I imagine that CN had seen the benefits to the 4-8-4 power curve from progressive improvements, and in particular from the internal streamlining applied to the late builds, and figured that similar updating of the 4-8-2 would deliver a power curve that met or more than met the power-required curves for fast passenger service, at least east of the Rockies.

  by Allen Hazen
Hypothesis on why CN went form 4-8-4 to 4-8-2 in 1944... makes sense to me. Since B&M wanted the locomotives primarily for freight, with only occasional passenger use... maybe THEY woud have been better off with something else!
  by Engineer Spike
I've read that B&M was less than thrilled with the T1 class. One drawback was that the drawbar to the tender was via the trailing truck. The buff forces caused the trailing truck to derail often. This may have been able to be solved if there was a way to connect the tank's drawbar directly to the locomotive frame. Perhaps the giant firebox size somehow precluded this.

I have to thank you guys for helping me get my head around this. The replies were well thought out. I can appreciate the ideas of all forces involved form my schooling as a "smart" engineer, before becoming a dumb one (L. E.).

For some more information, the R1 class was used frequently in passenger service. Having the 2 axle lead truck was a good attribute in fast service, as opposed to a single axle. It seems like especially the trains from the New Haven, in Worcester, to Maine were one prime=ary passenger assignment. One source said that the R1 was preferred because of the larger tender capacity on this long run. The only main line coaling facility that I know of was I East Deerfield. Who knows if a P4 Ould have been strong enough to handle these packed summer trains, or if it was just the fuel situation.

There were 4 subclasses of R1s. The last differed by having centipede tenders, and also Worthington feed water heaters, instead of Coffin. Back group came in the odd numbered years between 1935-41. All but the las group were sold to B&O, and lasted past any steam on B&M.
  by Allen Hazen
...and I've long wondered why B&O didn't buy the last group: as the newest, they would have seemed the least worn-out! Maybe there was some financial reason (locomotive purchases are typically done in trust arrangements with a bank being the technical owner for the first ten years). Or maybe the B&O didn't like the look of centipede tenders!
  by Allen Hazen
...and I've long wondered why B&O didn't buy the last group: as the newest, they would have seemed the least worn-out!
Maybe there was some financial reason (locomotive purchases are typically done in trust arrangements with a bank being the technical owner for the first ten years).
Or the B&M, seeing that they were new, quoted a price the B&O didn't want to pay.
Or maybe the B&O didn't like the look of centipede tenders!
  by Engineer Spike
I think that I remember something about the pace of diesel delivery having something to do with the retention of the D subclass. They would have been restricted to the New Hampshire and Portland Divisions, since the electrification was shut down in Hoosac Tunnel. The T class Limas were also sold off to SP and ATSF.