GP-40 … issues?

[Allen Hazen]

I recall reading somewhere that every GP-40 built went back to the factory for (under frame?) modifications. And I have seen a photo of a plain-black GP-40 identified as a loaner, built by EMD to substitute for units back "home" undergoing modification. (I think the unit was, after the end of the program, sold to the CMStP&P.)

What I haven't seen is any explanation of what this was about. Can anybody tell me what it was about the GP-40 that required after-sale modification by the builder? Or any other details about this episode?

[SSW9389]

First the easy part. There were 20 EMD GP40 Loaners. They were all built in May 1969 on two different orders 7179 and 7180. Serial numbers were sequential. See http://utahrails.net/ajkristopans/40SERIES.php#gp40" onclick="window.open(this.href);return false; for the order numbers and serial numbers.

The 20 Loaners were: EMD 11-20 to PC 3260-3269; EMD 21 to TP&W 1000; EMD 22-26 to PC 3270-3274; and EMD 2068-2071 to CMSP&P 2068-2071. Frame research pending.

Ed in Kentucky

[SSW9389]

See Evan Werkema's Santa Fe Subjects Site. It says cracked frames were the reason for building the 20 EMD Loaners. http://atsf.railfan.net/gp40/" onclick="window.open(this.href);return false;

The Annual Motive Power Survey in the January 1970 issue of Extra 2200 South notes that the Loaners were built while frames were corrected on other railroads GP35s and GP40s. See note 1 page 16. Also states that some of the Loaners were built in April 1969.

Ed in Kentucky

[Allen Hazen]

Thank you, Ed!
The account on the "Santa Fe Subjects" is very informative: more so than many things on the WWWeb.
--
Frame cracks. I suppose EMD based the GP40 frame on the GP35 frame… but lengthened a bit, supporting a heavier engine, and maybe subjected to a bit more stress on a more powerful locomotive with (at least after IDAC was added) better adhesion control so more of the power could translate into stress at lower speeds, and… Predicting the effect of repeated stress on complex metal structures isn't easy.

Thanks again. The question had been niggling in the back of my mind for a while.

[bogieman]

"Frame cracks" is a pretty broad description. While the GP40 used an underframe very similar to the constant section GP35, the cracks that occurred had nothing to do with the more powerful engine. The cracks occurred at the weld between the center bearing and the bottom plate. The EMD swinghanger truck has a center bearing about 18" in diameter and 10" tall welded directly to the bottom plate. Prior the GP40, all were welded inside and out - the center bearing is hollow with about a 10" diameter hole in the bottom for access to weld the ID. On the GP40 early production, the welding was simplified to weld only on the OD, which proved to be a bad mistake. A single-sided weld in an alternating fatigue load environment is effectively already "cracked" and it's usually only a matter of time until that crack propagates to the outer surface of the weld. The obvious fix is to weld it on the inside and grind out the outside to beyond the extent of the crack and re-weld that area. In production, the underframe is upside-down so the welds can be made down-hand, it's a confined area with poor visibility on the ID side. A skilled welder can do it overhead to make the repairs, but it is time-consuming. Suffice it to say all swinghanger truck center bearings have been welded inside and out in production since.

Dave

[Allen Hazen]

Bogieman--
Thank you for that explanation. "Pushing" technology can be dangerous, so I was assuming that the increased power and size of the GP40 over earlier GP types was the ultimate cause of the problem. From what you say, however, it was an attempt to reduce labor and cost in production: also a known potential source of … issues.
Thanks again!