• 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 Allen Hazen
QUESTION: The PRR regeard its PA-1 units for lower speeds when they reassigned them from passenger to freight service. Does anyone know exactly when this was done? (And, second question, is it likely that -- at the same or a different time -- they would have replaced the original motors with newer ones?)
Relevant to some new information I have been sent.
As to the second question, the units were built in late 1948 and 1948. On the assumption that they had 752 motors, this would mean they had the original subvariant: 752 A or 752C, I think. By the early 1950s GE had an upgraded version of the 752 motor, and for what was for the time a high-horsepower freight unit the up-rated motors might have been desirable.
  by jr
Withers Publishing put out an eleven volume set of softcover books on PRR diesels in the 1980s and 90s. Each major model has a chapter devoted to it, and each chapter has a page or two, of technical detail.

Paraphrasing some information from the chapter on PAs and PBs:

By the early 1950s, PAs were increasingly assigned to more demanding mail train service. This caused traction motor overheating. Therefore, in 1951, they started adding vents to the noses of PA's to increase cooling air flow. No mention of corresponding problems or modifications to PBs.

In 1952, original 726 motors were replaced with 752 motors in an effort to solve the overheating problem

[And addressing Dr. Hazen's most recent question] In September and October of 1954, PAs and PBs were re-geared from 60:23 to 64:19 and reclassified AFP-20 (Freight/Passenger)

And a side note from the chapter on Erie-Builts, the data sheet shows them has using the 746 motor.

  by Allen Hazen
So, the change in traction motors came before the re-gearing. (PRR didn't, I think, re-gear the PB units: the Alco boosters continued to be used in passenger service, in otherwise E-7/E-8 consists, even after the PA cab units were transferred to freight service.)

As I said earlier in correspondence with JR, the reference to 726 motors here is VERY surprising. The PRR's PA/PB units were of the sub variants Dl-304A (cab units) and Dl-305A, and were built in 1947-1948. Other sources say that this subvariant of the PA series was built with 752 motors. My suspicion (though I hate to be in the position of imputing errors to a source) is that there is an error here: perhaps the 1952 change in traction motors was to replace the original motors, which would have been of (one of) the earliest submodels of the 752, with the more robust later 752 type available after 1950, and the author of the page in the Withers volume, seeing in a PRR document that more robust traction motors had been installed, assumed that the less robust ones must have been 726. Burt I find the whole matter very confusing.

(And I'm very grateful to JR for sharing some new information on this old, but still surprising, string!)
  by jr
Regarding the gearing on the PB's, according to Withers:

They were re-geared "by 1957", returning to the AP-20 classification, and assigned to the passenger pool to work with E7s and E8s. They subsequently returned to the AFP-20 classification "by 1960".

It seems unlikely that PRR would re-gear the PB's twice, in their waning years before retirement (which happened in September, 1962). Certainly not impossible, though.

Withers cites internal PRR documents MP-229, which was put out on a monthly basis, and 109-L.