A1A truck compatibility question

Quick replies (busy day ahead)
H.F. Malone: Good point. Center plate diameters would be something for someone with access to ancient Alco or New Haven records to try to check! As for changing gears on traction motors: yes. PRR (perhaps not quite as desperately hard-up in the 1950s as NYNHHRR, though we know it wasn't rolling in spare cash!) did change the gears on the motors of its PA-1 locomotives when it decided that it would use EMD units on its regular passenger runs and re-assigned minority-brand passenger units to dual service, reducing their top speed from 100m.p.h. to 80 but improving their continuous t.e. ratings. (George Ellwood's "Fallen Flags" site has both PRR and NYCRR diagram pages for PA-1 locomotives: the PRR diagram gives stats for the units AFTER regearing, the NYCRR diagram for the units with their original gears: fairly dramatic difference in low-speed performance, but a 90m.p.h. PA-1 would still have been capable of doing some freight work for a few years before retirement on the NYNHHRR.)

Engineer Spike: Yes, I'm pretty sure that the New Haven's Alco 244-engined power all had 752 motors. The 752, however, had a significant upgrade around 1950: the RS-2 would have had "first generation" 752 motors (752A or 752B), and the RS-3 the upgraded version. Somewhere in the "PA-1 traction motors" string on the Alco forum there is a post (from "Typewriters") comparing the amperage limits for the different 752 subtypes.

I'll try to get back with details (Kirkland's book on Alco diesels has some relevant numbers) later.

Thanks, both of you, for your comments!

It said that the 2s had 65 mph gearing, while the 3s had 80 mph.

Same data source (T.T. No. 8).

Yes, maximum speed for the RS-2s was 65 m.p.h. while maximum speed for the RS-3s was 80 m.p.h. I just didn't bother listing every maximum speed for every engine on the roster at the time, just the ones we were discussing.

Like I said, my comment was only based on the fact that the 0760 class was built before the 0500. Since the RS2 was less capable, I made the assumption. Thanks for clearing it up.

Looking at Kirkland's book(*), I see a potential complication in the RS-2 story. A few early RS-2 (some but maybe not all of those built to specification E-1661) were built with GE 726 motors. The 752 motor was introduced a few months into RS-2 production: all RS-2 built to specifications E-1661A, E-1661B and E1661C had 752 motors: this covers something over 90% of the total RS-2 production, starting in March 1947. I'm going to assume (let me know if you think I'm wrong) that the New Haven's RS-2 were of the 752-equipped variety. (Engineer Spike, previous post, says that the New Haven PA-1 were built before its RS-2, so it seems safe to assume that its RS-2 -- the 500 class -- were of the later, majority, variety.)

(Just in case: continuos tractive effort for a 726 equipped RS-2 was 34,000 pounds at 13.5 m.p.h.)

With 752 motors -- RS-2 would have had 752A or 752B, sub models that seem to have been produced concurrently and differed only in details of how the lubrication was handled -- geared for a top speed of 65 m.p.h., they had c.t.e. of 42,500 pounds at 11 m.p.h.

The RS-3 replaced the RS-2 in Alco's production in May of 1950. I think the standard traction motor for the RS-3 was the 752C, which was significantly more robust.(**) RS-3, geared for a top speed of 65m.p.h. had a c.t.e. of 52,500 pounds, at about 9.6 m.p.h. They were also available geared for higher top speeds: 74:18 gearing for 65m.p.h. (this seems to have been the most common gear ratio for 752 motors on Alco and GE locomotives until at least the mid 1960s), 65:19 for 75m.p.h., 64:19 for 80m.p.h. (this would be what the New Haven had), or even 62:21 for 92m.p.h.

The higher-speed gear ratios yielded lower c.t.e. Another source(***) says that the c.t.e of an RS-3
----geared for a top speed of 75m.p.h. was 46,000 pounds
----geared for a top speed of 80m.p.h. was 43,000 pounds, and
----geared for a top speed of 92m.p.h. was 38,000 pounds.
So the New Haven's high-speed RS-3 would have had almost exactly the same c.t.e. as its low-speed RS-2, probably (given the slightly higher horsepower) at a speed a fraction of an m.p.h. higher than the RS-2's continuous speed.

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(*) John F. Kirkland, "The Diesel Builders, volume two: AmericanLocomotive Company and Montreal Locomotive Works," Interurban Press, 1989
(**) Kirkland doesn't give all the details in his paragraphs on the RS-3. I've compared his data on FA/FB locomotives (which had essentially the same mechanical and electrical gear as contemporary RS-2 and RS-3) and also the New York Central and Pennsylvania Railroad locomotive diagrams available at George Ellwood's marvelous "Fallen Flags" rail image website.
(***) Gear ratios, top speeds and c.t.e. offered on RS-3 are from "Early Diesel-Electric and Electric Locomotives" published by "Rail Heritage Publications." This appears to be a compilation, for sale to railfans, of entries from old editions of the (Simmons-Boardman Publishing Company) "Locomotive Cyclopedia": Simmons-Boardman held the copyright, dated 1983. The information in these entries would have been provided by the manufacturers.

Of course, all that data has to do with RS-2 and RS-3, and not with the Dl-109 and PA-1 locomotives we started talking about. But there are a few things that I think allow some plausible guesswork. Look first at the difference between an E-1661 (726 motors) and an E-1661A (752 motors) RS-2: geared for the same top speed, the 752 motors give a 25% higher c.t.e.

Now look at the different gear ratios available on the RS-3. Gearing for a top speed of 90 (well, 92) m.p.h. yields a c.t.e. about 11% lower than gearing for a top speed of 80 m.p.h. So my GUESS is that the New Haven's 90m.p.h. 760 class may have had slightly BETTER continuous tractive effort than its 80 m.p.h. 700 class! But in the same ballpark, so for simplicity it would be reasonable to give them the same tonnage ratings… using the bit of lee-way that provides to ensure that the freight people won't burn out the traction motors on first line passenger units when they borrow them.

But, to repeat, this part is guess-work on my part. Let me know if you think I've overlooked something relevant!