• 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 jr
I have a TP-800 manual that shows the weight for a 5GE752C1 as 7000 lbs, without pinion.

The TP-600 manual shows the traction motor for the 660 / 1000 hp engines as 5,600 lbs. I haven't found the model number, but believe it to be the GE731.

Don't have any corresponding data for EMD.


  by EDM5970
That is correct, jr, the 731 was the switcher (and RS-1) motor. And over on the Chevy forum, RAS posted that the 716 was used on the Rock Island TAs, an early 1200 HP light (and fast) passenger unit.

Sorry I don't have actual weights for the different motors; in fact I have very little EMD data. The "twice the weight" comment was the opinon of my MM friend, based on how much his forklift struggles with a 752.
  by Allen Hazen
Thanks, jr, for the weights!
EDM: My "They're all about three tons" was a sign of my ignorance! I ***THINK*** I once read somewhere that an EMD traction motor -- I have no idea which model -- weighed something in the range of 5900 pounds: which is enough less than the 7000 jr quotes for a (pinionless!) 752 for your friend's forklift to feel the difference!
As for what the extra 1400 pounds gets you if you have a 752 motor instead of a 731...
While trying to find an answer to a question about the S-6 I came across a comparison between the S-2 (1000hp and 731 motors) and the T-6 (1000 hp but 752 motors): The S-2 has a continuous rating of 34,000lbs at 8mph, whereas the T-6 is rated at a whopping 53,000 at 5mph! (And that's using the 74:18 gear ratio for the T-6: a gear ratio standard for Alco and GE freight types with top speeds of 65 or 70mph. As far as I know all 731-motored locomotives had a switcher-optimized gear ratio with a bit more reduction: 4.6:1 as opposed to the T-6 and freight units' 4.1:1.)
Note that one of the late MLW switchers (I think the S-13: 1000 hp, 251 engine, front-radiator carbody) was offered with either 731 or 752; the version with the bigger traction motors was thought of as a hump pusher.
  by EDM5970
I had the opportunity to walk past two trucks, without motors, sitting on the ground yesterday. One was an EMD Blomberg, the other was from an Alco FA. I didn't have tape measure in hand, but the bolster on the EMD truck, with its 108" wheelbase, was quite noticeably wider than that on the 112" wheelbase Alco truck. (I just looked those two dimensions up in Diesel Spotterd Guide.)

I remember measuring the center plate socket on these same two trucks awhile ago. If memory serves, the Alco socket was either 16 or 18 inches, while the EMD was 22 or 24 inches in diameter; quite a difference. Also, the Alco socket overhung the edge of the bolster, while the EMD was contained within the width of the bolster.

So, with the thinner bolster, and the 6 inch longer wheelbase, Alco/GE had several inches more room to mount bigger motors in. Nothing earthshaking, just an observation-

The normal gear ratio for an RS-1 and the 539 switchers is 75/16, which would allow 60 MPH operation. (I've been on an RS-1, light, at 60, on the old NYC main, and it did just fine-) But I have a reprint of an article from the February 1942 Railway Mechanical Engineer, (Newton K. Gregg Train Shed Cyclopedia no. 58) which lists the RS-1 as having 73/18 gearing, 70 MPH. I wonder how many were built that way?

The same Gregg reprint has an article from the May 1942 RME, which shows the New Haven DL-109s as having 726 motors, geared for 80 MPH,
with no gear ratio mentioned. (Mr. Telesha had already brought this up.)

Also, I found a note that I pencilled into an RS-1 DRP, showing the 1325/24 AWG TM cable (535 MCM) being good for 828 Amps, although that 828 A. is based on using the new Exane wire. But this should give an idea of the current capacity of the 731s. The 539 switchers and the RS-1 started in full series, while most of the 752 stuff, with the exception of the 251 switchers, start in series parallel.

More grist for the mill, I guess-

  by Allen Hazen
Thanks again!
1) A number of U-boats (U36B, U33B, U30B, U23B, U18B, for SCL, AT, C&O, WP and maybe some other customers) were built with Blomberg trucks: most sources say "from EMD trade-ins," but I vaguely remember reading somewhere once that new truck castings were used on some. So apparently it is POSSIBLE to modify a Blomberg to accommodate GE 752 motors-- from your description, though, it sounds as if the modification might involve installing a new bolster of very different dimensions. (If anyone else reading this string knows more about this... please?)
2) Your post has the first indication I've seen that any locomotives were built with 731 motors using any gear ratio OTHER than 75:16, so thank you very much! 70mph gearing on an RS-1 might seem odd, but if it was intended for operation on the New York Central main line (Central used RS-1, along with comparable Baldwin and Lima models, for commuter train power)... Even if the train the RS-1 was pulling was an all-stops local, it might have been considered essential that it be ABLE to sprint occasionally to get out of the way of faster services: nobody wanted to have to tell the passengers on a delayed 20th Century Limited that they had been held up by a commuter local! So I suppose there might have been a bit of a market for 73:18 RS-1.
  by Allen Hazen
My suggestion that the New York Central might have been in the market for 70mph geared RS-1 was just a "for example." Checking the New York Central locomotive diagrams on George Elwood's "Fallen Flags" site, there seem to have been several diagrams for different batches of NYCRR RS-1, but the only one actually available at the site shows 75:16, 60mph. (There are also several Pennsylvania Railroad RS-1 diagrams available at "Fallen Flags": I looked at the ones for passenger units ["s" -- for steam generator -- suffix on the PRR class designation], and they all specified 75:16.) So, question for RS-1 experts: even if Alco-GE offered the type with 70mph gearing, were any actually built with 73:18?

  by 498
Allen, going back a couple of steps, you are real close on that weight for the EMD traction motor. The official EMD component weight list which used to be published occasionally by the parts department showed a weight of 6200 Lbs. for the D77 traction motor including the shipping skid. (2/1/82 edition, inside front plate)

  by EDM5970
That reprinted article from Railway Mechanical Engineer concludes with the statement that "Road switchers of this type have been delivered to the Atlanta & Saint Andrews Bay, the Chicago, Rock Island and Pacific , the Chicago, Milwaukee, St. Paul & Pacific, and the Tennessee Coal, Iron and Railroad Company." There is a photo of the TCI&RR unit, which also had the US Steel logo.

Given the date (February 1942), it is possible that some of these early units had higher gearing, before things got more standardized, or it may be like the never built 251 powered FA-3; something that was offered (as an option) but never ordered. I'll peruse Kirkland, Draney and Steinbrenner over the next few days.

Going back to the issue of trucks, a thinner bolster may be the answer, or a bolster that has the TM nose suspension springs recessed into a pocket. Hopefully someone familiar with the models and roads Allen listed will have a real answer. (Or...could the sideframes have been lengthened a few inches? Nah, that would require new brake rigging, spring rigging, etc. Just thinking out loud-)

  by Allen Hazen
Thanks for the weight. D-77 is the version ??? used on Dash-2 models ??? Things (this seems to be an almost universal law of engineering) get heavier over time, so one of the earlier versions might have weighed a bit less. Or the weight I saw quoted didn't include the shipping skid. Or I misremembered.
A lot of railroads bought RS-1 after 1942, so... I have the Kirkland and Steinbrenner books, and have been going over them obsessively in the past few weeks looking for traction motor information (Grin!). What is the Draney book you refer to? It's not a familiar name to me.
Modifying a Blomberg to accept GE 752 motors would, I guess, almost certainly involve doing something at the bolster end of the traction motor: to lengthen the wheelbase would involve a whole new truck frame casting, which is surely the most expensive part of the structure! But I've never seen any details about what is involved. (Come to think of it, GE isn't the only company to market locomotives with 752 motors in Blomberg trucks-- didn't Southern Pacific ask for GE motors in some of its GP35?)

  by Engineer Spike
Along with one of Mr. Hazen's posts. I remember reading that New Haven's RS2's had 65/70 mph gearing. Would it havethe 726?
The point was that the RS3 had faster gearing and the 752 motors, but was able to have the same minimum continuous speed, and or TE.

  by pugsley720
"Allen Hazen" wrote:

"Thanks for the weight. D-77 is the version ??? used on Dash-2 models ??? Things (this seems to be an almost universal law of engineering) get heavier over time, so one of the earlier versions might have weighed a bit less. Or the weight I saw quoted didn't include the shipping skid."

Been enjoying this discussion a good deal, I worked in the coil shop of a large remanufacturer of traction motors for just over 21 years. (Now a division of GETS) While we were primarily an EMD rebuild facility when I was there, we did do some GE coils also.

To the best of my knowledge, your assumption is correct for the version of the EMD motor. For the most part all EMD motors from the D-47 through the D-78 are basically the same, at least as far as the coils were concerned. Only major differences that I was ever aware of was bearings or armature insulation, both of which were constanty under revison/improvement, bearings more so than insulation. Both EMD and GE settled on polyimide based wire enamel and polyimide film with fiberglass tape outer insulation for armatures prior to my employment starting in 1979. It was simply far superior to the old mica insulation of the earlier model series.

The D-78 used essentially the same armature as the D87A, and the major difference in those from the D-77 was copper size for the conductors and the conductors were transposed within the cell section of the core iron to help control eddy currents and reduce heat.

GE field and aramture coils were substantially larger that EMD. An EMD main field weighed around 102 pounds without pole iron, a GE 752 E series main weighed about 125 pounds if I recall correctly, and that is without the pole piece. The A series (AF, AG) weigh even more. As a side note, "back in the day" when there were a number of us "young bucks" in the shop in the late 1970"s, one of our favorite tests of manhood was to see who could lift a bad order 752 main potted on its pole piece the the highest...well over 200 pounds. Today that practice would earn you some swift discipline, and we all wonder why we have bad backs! :wink:
  by Allen Hazen
Engineer Spike--
I don't know about the New Haven's RS-2, but (according to Kirkland's book) early RS-2 (like early FA-1) had 726 motors, with a switch to 752 motors in later production. So at least some of the New Haven's units may have had the earlier motor. (After 1950, GE came out with an upgraded version of the 752, which would have been used on RS-3. With the same gearing-- 74:18, giving a top speed of 65 or maybe 70mph, was standard-- there would thus have been TWO improvements in continuous speed and continuous tractive effort for Alco roundnose roadswitchers: one between the early and late RS-2, and another for the RS-3. I'm not sure which is relevant to the New Haven.)

Tests of manhood just don't impress the OSHA! (Grin!) My impression (vague recollections of articles I didn't fully understand, in "Railway Age" and other places) is that both GE and EMD made major improvements in their traction motors around 1979: better motors were needed for high horsepower locomotives with EMD "Super Series" (GP-50/SD-50) and GE's "Sentry" (late Dash-7) wheelslip/adhesion systems.

An RS-1 feature in "Extra 2200 South" in the 1970s (I can check the exact issues if you want bibliography, but don't remember off hand) says that ALL RS-1 were built with the 75:16 gear ratio, which if true means that you are right in guessing that the 73:18 option was like the "FA-3". But I don't know how much weight to put on the "E2200S" information.

(And thanks to all-- I'm learning a lot from this string!)

  by Allen Hazen
For those interested-- a related string (on EMD locomotives built with trucks from Alco trade-ins) has recently (November 2005) started on the Railroad.net EMD forum.
  by kajefreak
Can anyone tell me what the difference between a D77 and a D78 and a D47 are?
Just started in the field about 6 months ago and enjoying it.
but some Q i have cant get answered at work because of the work in progress theres no time.
any info would be appreciated
Ive been told the difference is in the armature ...the frames are the same and so are the coils.
and if so..........
then does this effect the horsepower or the speed.
when we volt drop them the get the same readings in the coils.
Curious Kaje

  by pugsley720
In as few words as possible, the biggest difference between a D47, D77, and D78 is bearings and insulation. These two items were and likely still are constantly under development and improvement.

For the long answer, based on my experiences at at my former employer, the field coils for D47 through the D78 are the same and pretty much interchangeable. D47's would come in as unit exchanges, and as long as the conductor copper was within spec, they would be rewound and shipped out as D77 or D78, whatever the customer ordered. They all used the same size conductors, and the same pole pieces. There were minor changes in insulation over the years as technology advanced, especially in turn to turn materials. The earlier D37 used smaller conductor stock. The even earlier D27 used yet another size conductor and a different winding, being a 7 turn and a 9 turn winding in series on each main pole vs. two 8 turn windings for all EMD motors from the D37 through the D78. The D27 and many D37's used an older mica/resin groundwall insulating system, the D37 also saw the introduction of silicon rubber groundwall insulation on EMD motors, which is still in use today.

The armatures had differences in conductor size and/or insulation from one model to the next, to gain power from the motor or reduce heat and increase motor life.

The D78 utilized a different armature winding than the D77, basically a D87 style armature in D77 coiled stator frame. The D78 coils had a larger conductor cross section, and the conductors were transposed in the slot cell section, the D77 and earlier were straight wound through the coil. This change was intended to control eddy currents and reduce heat, thereby increasing motor life while increasing power. The slot wedges and insulation between the coils within the slots changed from D77 to D78.

Bearings, commutators, and insulations were constantly being upgraded, the search for higher dielectric strength, cooler running, and longer life was never ending. This led to subtypes of the various motors, just as the 567 and 645 prime movers have variations, the traction motors have variations depending on upgrades in bearings or other technology, such as D77, D77B, and so on.

Hope this helped some.