• PA-1 traction motors

  • Discussion of products from the American Locomotive Company. A web site with current Alco 251 information can be found here: Fairbanks-Morse/Alco 251.
Discussion of products from the American Locomotive Company. A web site with current Alco 251 information can be found here: Fairbanks-Morse/Alco 251.

Moderator: Alcoman

  by kajefreak
Yes that helped out a lot.
It explains why every one has a different answer to the Q..lol
so does it wont hurt if you have a bad 78 frame and use the arm in a 77 b frame...right????
thats what we are working on now.
shouldnt hurt...?
but then does that make it a 78
and the next one is a truck that has 3 77s in it and one 47
my co worker said he was surrprized it didnt derail the train because of the difference in power.
but they are pretty much all the same ...just made differntly right.
thanks again for the help......really appreciated.

  by pugsley720
Again, this is based on what I recall from work, and I have been out of the field for several years now, so take it for what it is worth.

When you say a D78 frame and a D77B frame, I am going to assume (I know, never assume :-D ) you are referring to the coiled frame, and not just the frame the fields are placed in. I worked in the coil shop, the motor line was elsewhere, but from what we were told, a newer model EMD frame was an EMD frame, the armature coils and bearings made the difference between the D47 through D78 line. The major field coil changes occured in in the later D87 series.

Bear in mind, there were cast and fabricated frames, and an older style frame which I recall discussion of, something along the lines of wide and narrow window frames, but I cannot recall which is the newer style at this point. This had something to do with the end bells and bearing supports I believe.

The field coils from D47 to D78 are identical, so you should be able to put a D78 armature in a D77 coiled frame, provided you have the correct bearings, caps etc. Would it be a D78...I am not sure. That may require a check of EMD manuals to see if you have the correct parts. I am pretty sure there are a lot of mixed and matched motors in service, that is one good thing about EMD products, parts are interchangeable. If your D47 frame grounded the number 4 interpole coil, you can replace it with a D77 equivalent and it will work just as well as a new D47 IP. I recall there may have been a minor change in the air (cooling) baffles that go on the side of the coils at one point, but the new style is totally interchangeable with the old, so it would not make a difference.

Again, this is based only on my memories of what we produced in the coil shop, but after the mid 1980's we made only one style armature coil for pre-D87 motors, a D78 equivalent. There simply was no demand for the older D77 style any longer. The D78 was considered equivalent to and a direct replacement for a D77, and was an improvement in operation and performance, not so much a huge increase in power. All I know is we sold a lot of them.

I don't believe that there was a huge rating difference between a D77 and a D78, the D78 was an improvement in the armature windings that in the eyes of EMD warranted a new model number rather than another sub-model in the D77 line.

As far as mixing motors in a truck, that is out of my line. I do recall another thread on this elsewhere, and I believe this is also a common practice, provided the motors are of a similar series, such as your D47 in among a group of D77's. The difference in windings is not that huge that it should make a great difference, the D47 may run hotter and have a shorter life as a result, but I doubt it would derail the train. I think you might get into trouble mixing a D87B and a D27 in the same truck though!
  by kajefreak
Just wanted to thank you for the advice.
and i will continue my quest for knowledge elswere.
it was nice meeting you.
once again thanks.....you could have just blown me off....lol
I plan on moving up through the ranks in this field......the more in know the better off i am........
  by Allen Hazen
Just got my copy of "Extra 2200 South" issue #130. Their running series on the Santa Fe's diesel locomotive fleet has gotten up to passenger units (other than passenger EMD Fs), and has a few bits that ... make things even more confusing.
1. The prewar ("Needlenose") Alco passenger units (the roster calls them "PA" and "PB", distinguishing the postwar units as "PA1" and "PA2") are shown as having ... 726 motors. Since I don't think the Santa Fe thought of them as dual-service units, this conflicts with the testimony of another source (Kirkland's book, I think-- now I'm on the wrong continent to consult IT) that the 730 motor was used on pure passenger units in the Dl-100 series (with three different gearings for 120, 100 and 80mph top speeds) and the 726 (with a different 80mph gear ratio) for dual service units.
2. As for the postwar units the rest of us call PA and PB... The "E2200S" roster shows the first 24 (first eight ABA sets), built between the end of 1946 and early 1948, as having 746 motors, with the later ones, built starting in late 1948, as having 752 motors. On the other hand, Jim Boyd's "Passenger Alcos" shows ALL of the Santa Fe's units as being built to the first production subvariant (Dl-304/Dl-305 with no suffix letter-- Dl-304A/Dl-305A being the second subvariant). So, if (IF) both are right, the change from the "plain" to the A subvariant was about something OTHER than the traction motor model used. And if the contemporary "Railway Mechanical Engineer" article reprinted in the "Model Railroad Cyc," which depicts first Santa Fe units and lists them as having 726 motors is ALSO right... the change from 726 to 746 must have involved retrofitting the first units built: maybe after testing on the Lehigh Valley but before delivery to the Santa Fe??????

I've left my copy of the magazine at home. I'll post actual gear ratios in my next post.

It would be interesting to know what sources the compiler of "E2200S"'s roster used....

  by Allen Hazen
Some gear ratios.

---The 50 and 50A (Dl-107/Dl-108 according to a roster of Dl-100 series locomotives in the May 1984 issue of "Mainline Modeler") is listed as having 58:25 gearing. According to the December 1946 "Railroad Mechanical Engineer" article reprinted in "Train Shed Cyclopedia #64" (sorry, got the title of the reprinting wronmg in my last post), that gear ratio with 726 motors is good for 117 mph. (Comment: no wonder the Santa Fe assigned those two units primarily to runs in the Midwest: they can't have been very good at climbing mountains!) ... I'll discuss this further in a later post: maybe start a new string "Dl-100 traction motors")

---The 51 class (PA1 with, according to "E2200S," 746 motors) had a gear ratio of 64:23.

---The 90 class (F-M "Erie Built" units, all of which supposedly had 746 motors) had a gear ratio of 63:24. According to a November 1946 "Railway Mechanical Engineer" article on the Union Pacific's first Erie Builts (repr. in the same Train Shed Cyclopedia issue), an Erie Built with that gear ratio and 40" wheels was good for 102 mph. Query: WHY, if they were ordering 2,000 hp. A1A-A1A units for the same service from two manufacturers with the SAME model of GE traction motor wouldn't the ATSF have specified the same gear ratio? In the event, the difference doesn't seem to have mattered: the Erie Built units, though generally less successful and usually kept off the transcontinental trains, were sometimes multipled with PA1 units.

---The 59 class (PA1 with, according to "E2200S," 752 motors)had 61:22 gearing. As a ratio, this differs by less than one percent from 64:23. Since I have seen nothing to indicate that 746 and 752 motors were optimized for different rotational speeds(*), this sounds as if the intention was to make the 51 and 59 classes functionally equivalent despite the change in motors, with a top speed of about (this from approximate mental arithmetic) 97 mph.

---The 350 and 400 classes (much later: U28CG and U30CG) had 752 motors with 77:26 gearing; "The Diesel from D to L" by Vernon L. Smith (Kalmbach, 1979: reprinted from "Trains" issues of April through July 1979) says they had a top speed of 93mph.


(*) When this string was active in 2005, I did the arithmetic for as many gear-ratio/top-speed combinations as I could find for 2000hp A1A-A1A units frpom Alco and F-M: the traction motor rpm at top speed was very close to the same (always about 2250rpm as I recall) for 730, 726, 746 and 752 motors.
  by mxdata
From ALCO Spec. DL-304-B (September 1947)
for the "2000" Road Passenger Locomotive

Traction Motor Specified: GE-752

Gear Ratios listed:
64:19 (80 MPH)
62:21 (90 MPH)
60:23 (100 MPH)
58:25 (117 MPH)

  by Allen Hazen
Thank you thank you thank you!!!!!!!! I have an awful feeling that editing and proofreading of Alco documents may not have been perfect (too many problems with model numbers, etc, have been mentioned over the years), but technical details in the original specification OUGHT to be trustworthy.
So, FOR ONCE, we don't have to speculate on the basis of railfan scholarship.
Thank you!
(1) The motor speeds for the four gear ratios mentioned at the stated top speeds are:
64:19 (80mph) -- 2264 rpm
62:21 (90mph) -- 2233 rpm
60:23 (100mph) - 2192 rpm
58:25 (117mph) - 2281 rpm
(On the assumption of 40 inch wheels: a complicating factor is that Alco apparently offered 42 inch wheels as an option on the PA, but for the moment I am going to assume 40".)

(2) The top speed listed for the 58:25 ratio is the only one that isn't a round number. My guess is that the Alco (or, probably, GE) engineers REALLY thought 2281rpm was about as high a speed as they thought was safe. (120mph at that ratio would have the motor going well over 2300.)

(3) The motor speed for the 60:23 ratio is low. Allowing the motor the sort of rpm allowed with the other ratios would give a top speed more like 102mph.

(4) I'll check it AGAIN when I get home, but I think the "E2200S" article gave a gear ratio of 61:22 for the Santa Fe's 59-class (PA1 with 752 motors)... which isn't on your list! This would give a 97mph top speed (at 2260rpm). Possibilities: (A) Typo somewhere and they really had one of the other ratios. (B) The Santa Fe had decided that 97mp was enough.
In support of (B), The 51-class (with, supposedly, 746 motors) had 64:23 gearing, which is very close to the same ratio as 61:22 (and, according the the New York Central diagram for Erie-builts, good for 97 mph on a unit with 746 motors).

  by Typewriters
Some of the line items from page 830, TP-400 manual for Road Locomotives with 244 engine. All given here pertain only to 2000 HP Passenger units. Not listed in any order.

746 motors, 64/23 gears, 42" wheels, top spd 101 mph, 1 step of shunt

746 motors, 64/23 gears, 42" wheels, top spd 101 mph, 1 step of shunt
(differs slightly in transition relay pickup speeds from above)

752 motors, 61/22 gears, 42" wheels, top spd 101 mph, 17 steps shunt

752 motors, 62/21 gears, 40" wheels, top spd 91 mph, 2 steps shunt

752 motors, 64/19 gears, 40" wheels, top spd 80 mph, 17 steps shunt

752 motors, 62/21 gears, 40" wheels, top spd 91 mph, 17 steps shunt

752 motors, 60/23 gears, 40" wheels, top spd 104 mph, 17 steps shunt

752 motors, 58/25 gears, 40" wheels, top spd 117 mph, 17 steps shunt

These are entries in a table giving setpoints for transition relays, overspeed warning and overspeed trip relays. The date of the page is August 1949. No 726 motors are listed. Only 746 and 752 motors are given for 2000 HP passenger units. Units with 17 steps of shunt employ the multipoint shunter known to have been developed later on.

-Will Davis

  by Allen Hazen
Will Davis--

Thanks! I will have to take time to digest all that. Do you have a date for the TP-400 manual that the figures come from?

Not surprised that there is no mention of 726 motor: if they were ever installed on post-war 2000 hp units, I think it would only have been for the initial testing (the tests on Lehigh Valley? between 6-46 and 10-46?) of the first units built: unless the "E2200S" roster is badly mistaken, these units were re-equipped with 746 motors, I'd guess before the units were delivered to the Santa Fe.


It's easy to make mistakes copying down lists of numbers (I know!), so I DID check after I got home last night. The "E2200S" roster DOES say what I said it said in my reply to mxdata.

  by Typewriters
As I mentioned, the particular page on which the chart quoted from is dated August 1949 and the entire manual, on the front page is dated October 1949 -- so you'd have to assume, or at least have to HOPE that all of the variations running around at that point were tabled in the manual.

As another note there are some revisions entered in this (quite pristine) manual through April 1950 but they do not affect the sections under discussion here.

I'll look around here a bit more and see if anything else can be discovered relevant to this discussion.

-Will Davis

  by Allen Hazen
Will Davis--
Thanks! I was in a hurry to leave my office yesterday and didn't read your posting carefully enough. Sorry.
PURE speculation, but I think I can see the outlines of a story which would be consistent with the data... at least the data I've seen so far. ... With a few loose ends.

Relevant facts about dates:
(A) The Gear ratios mxdata listed (thanks, again!) are from the spec for 304B/305B. This was the third production variant (the last at the 2000hp rating). So it seems possible that by the time it came out Alco was trying to rationalize the options a bit, and only advertised these four gear ratios for this variant.
(B) Santa Fe, which had started with 746 motored units, was getting (acc. the "E2200S" roster)their PA/PB units with 752 motors by 10/48. So it seems likely that Alco stopped using the 746 before that. So Will's manual covers earlier production, not just what was on offer in 1949. (Sorry-- that "fact" got about three conjectures tacked on to it!)
(C) The "Railway Mechanical Engineer" article that mentions the 726 motor (with 40" wheels and gear rattios late offeed with the 752 motor) was probably written at a time when only three PA-1/PB-1 units were in existence. (It was in the December 1946 issue; Santa Fe's second ABA set (52-52A-52B) wasn't built until November.)

(1) Before the first units are built, Alco and GE engineers working on the detailed design say "The F-M people want their locomotive to be dual-service, so we've sold them the big 746 motor. We are planning to market 1500hp B-B units for freight, so our big diesel will be a pure passenger unit, and the 726 is hefty enough for that service." The plan to use the 726 may or may not have lasted until sn. 75000,75001 (the A-B units later known as Santa Fe 51 and 51A) were built in June of 1946.

(Note: someone on another forum that I found by Googling "Santa Fe PA locomotive" claimed that at least these two units were built to specifications Dl-300 and Dl-301. This would mean that the specification got rewritten at least twice before the "production" Dl-304 and Dl-305.)

(2) Something makes them change their minds. Possibilities include: (i) odor of traction-motor-insulation smoke noted during tests on the Lehigh Valley in the summer of 1946, or (ii) the Santa Fe representative saying "We run trains over the Continental Divide, guys-- you've GOT to give us a better continuos rating than THAT!" (Train Shed Cyclopedia at office: I think it gives the continuous rating for the units supposedly equipped with 726 motors, and it's about 5000 pounds less than for units with 752 motors-- I'll check tomorrow.)

(3) Alco and GE engineers panic. "We can do it with the "726 New Generation" (or whatever they were calling it before introduction), but that's not going to be available for MONTHS!" So they decide to use the 746. Retrofitting the first two units, if they were originally tested with 726 motors, before delivering them to the Santa Fe in October 1946.

LOOSE END: So why go to 42" wheels and 64:23 gearing, instead of using 40" wheels and 63:24 (good for 102mph acc. to "RME" article on U.P. Erie-builts)? I don't know. (There are possible advantages to using larger wheels that aren't connected to traction motor characteristics: for example, slower wheel rotation might put less strain on the journal bearings. (Guesswork on my part.))

(4) By mid 1948 the "726 New Generation" is available (rebranded as the 752), and Alco-GE phases out use of the 746 on PA locomotives. Suggestion of reverting to 40" wheels produces loud complaints from Santa Fe (Standardize! Standardize!) so, to get the same speed rating a non-standard gear ratio (61:22) is used with 42".

LOOSE END: In mid-1947, Santa Fe takes delivery of three F-M Erie-builts (Santa Fe 90 class). They seem initially intended for the same service as the PA units (and were sometimes multipled with them), and were built while Santa Fe was getting PA units with 746 motors (last Santa Fe PA with 746 motors built 2/48). So... Why didn't they standardize and use the same wheel size and gear ratio? The Erie-builts come with 40" wheels and 63:24 gearing! (Maybe F-M was trying to standardize, and didn't offer the 42" wheel/64:23 gearing option? Somebody with access to Kirkland's "The Locomotive Builders, vol. I: Fairbanks-Morse and Lima-Hamilton" please check what he says about gear ratio and wheel size options for the Erie-built. Please?)

It's a hypothetical story fitting the data I have so far. Subject to revision in the light of further evidence: that's what hypotheses are!

  by Typewriters
Interesting!! A few randomized points...

The New York Central's 4400-class Fairbanks-Morse units (Erie-Built) did in fact have 42" wheels, 64/23 gear ratio and top speed of 97 MPH.

I thought that all F-M Erie-Builts had 42" wheels.

Some roads did make requests for wheel diameters to standardize. Some roads -- and builders -- felt that the increased wheel-to-rail contact patch offered by the 42" over the 40" was significant enough to warrant use.

It seems obvious that the table I gave figures from in the TP-400 manual covers all production variants, or at least all variants considered by ALCO-GE as production variants up to publishing date. (Note that I didn't include it but in the entries for the 1500 HP freight unit the 726 motor is NOT listed at ALL, indicating that the company likely viewed the GM&O units so equipped as a pre-production variant.)

ALCO-GE probably didn't originally desire a match with the Erie in the 2000 HP Passenger unit, vis a vis traction motor capacity and short-time rating because the ALCO-GE unit was not designed as, and never advertised as, a dual-service design .. which was the total underpinning of the concept of the Erie-Built in the first place. The ALCO-GE unit was very much lighter; on the NYC, roughly 310,000 lbs versus 333,000 lbs for the passenger Erie-Built and 348,000 lbs for the freight Erie-Built (all "A" units given there.) The weight on drivers of the freight Erie was about 232,000 lbs, roughly that of the early EMD F-units and ALCO-GE 1500 HP road switcher / road freight units, whereas that of the ALCO-GE passenger unit was only roughly 207,000 lbs. For such reasons, excessive traction motor capacity on the passenger unit probably seemed unnecessary to ALCO-GE since it couldn't really use the full output at truly low speeds for lack of adhesive weight. So I'm with you on that one.

Finally as regards AT&SF and their long-haul passenger trains; we all know that eventually the road decided that, for most services, locomotives with 2000 / 2250 HP riding on six axles only four of which were driving were not adequate. It changed to 1500 HP on four axles, all driving - lowering the minimum continuous speed, improving adhesion and from all accounts improving performance at the same time.

-Will Davis

  by Allen Hazen
As I remember Kirkland's F-M book (I'm an ocean and a continent away from my copy right now), the Erie-built was offered with either 40" or 42" wheels, and I couldn't see any system to the options (i.e. both wheel sizes were available for both freight and passenger service).

I'm afraid I misremembered what the "RME" article said when I posted last night. It claims that 62:21 geared PA (with, supposedly, 40" wheels and 726 motors) had a top speed of 90 mph (so far so good) and a continuous rating of 30,500 pounds. Since (this time according to the New York Central diagram on "FAllen Flags") the New York Central's PA1 (with 40" wheels, 752A1 motors, and 100mph top speed) had a continuous rating of 27,000 pounds (at 23mph). Something doesn't seem right here: maybe I need to do some more arithmmetic, but I would have expected a marked increase in capacity for the 752 over the 726. ... Unless, of course, the "RME" continuous tractive effort figures were for a unit with a different traction motor... (Grin!)

Will-- does your TP-400 manual give continuous ratings for the different gear-ratio/wheel-size options?

  by Typewriters
No, unfortunately TP-400 in that version does not have those; one "step" later in manuals and you get minimum speeds to run at should the ammeter fail, but not in this TP-400.

However, I note that the NYC's Erie-Built passenger units with 42" wheels, 64/23 gears and 97 MPH top speed were rated 29,000 lbs continuous effort at 21.9 MPH. Of course, that's 746 motors.

Comparing the units and noting the 900 Amp 752A in the ALCO-GE unit you quoted (2000 HP, 40", 62:21, 27,000 lbs @ 23 MPH) and the 1050 Amp 746 in the Erie makes one think that there's no way the 726 could have been good for over 30,000 lbs continuous with that gear ratio.

One must begin to wonder who was the first person to write, ever, that any ALCO-GE 2000 HP passenger units had 726 motors, and from where that information was obtained. That continuous figure you gave sure doesn't sound like 726 motors.. or 730 for that matter.

This might in fact be proof that the 726 actually was NOT used under any 2000 HP ALCO-GE passenger units --- and that's another good reason why NONE appears in the table in TP-400.

-Will Davis

  by Allen Hazen
Who FIRST said that 726 motors were used in Alco 2000hp passenger units? (Postwar passenger units: I think there is a fair bit of documentaion to the effect that the New Haven's Dl-109 had 726 motors.)

Well, the 1946 "RME" article is fairly early. One thing that shakes my confidence: I've gone over it, and there is only one occurrence of the number in the article. So maybe "726" was just a tyupo for "746"? Kirkland's Alco book gives continuous tractive effort for FA with 726 and with 752 motors, and there is a big jump with the 752: it does certainly sound as if the c.t.e. figure in the "RME" article is not right for 726 motors!

(Somebody with access to things I don't have access to: any figure for what the continuous rating of a Dl-109 was?)