Alternative History EMD: the "SD55"

[Allen Hazen]

Prompted by the "Why wasn't the SD-45 as popular as the SD-40?" sting, I have been rereading Preston Cook's excellent three-part SD-45 article in the May, June and July issues of "Railfan and Railroad."

--First installment confirms that the 20-645 (in the 645F version) continued in production into the 1990s for marine and stationary applications.

--The second installment discusses the maintenance problems. Crankshaft bearings were apparently a sore point: addressed both by tightening tolerances in EMD's engine production and urging the railroads to sharpen up their maintenance practices. The biggy, though, was the fact that
"...the early crankcaes were also found to have a tendency to crack the welds which attached the crankshaft supporting "A-frames" to the crankcase lower stress sheets. ... The problem was ... occasionally encountered on 16-cylinder engines as well, but by far the highest incidence was on the No.10 and No. 11 A-frames in the 20-cylinder, the two bearing positions forward of the very large rear main bearing."
Cure: improved welding techniques, and, from 1972 on, "A-frames which had a considerably enlarged foot in the shape of a letter "D" set sideways."

--Third part has the intriguing tidbit (after a description of the SD-45X test units)
"A 4200-h.p. "SD55" was offered by EMD in 1972 but was not included in the Dash-2 catalogue, and none was ever sold."
Comment: Not in the catalogue, and Cook puts "SD55" in scare-quotes: so this probably shouldn't be considered am "official" model number. The 645E3A engine used on the SD45X (as opposed to plain 645E3 on normal SD45) did, however, have features (such as the "rocking-pin" bearing for the cylinder wrist pin) that were used on the 645F engines on the later 50-series.

[mxdata]

The 4200 horsepower rating for the 20 cylinder 645E3A in rail service would be very consistent with the 4000 horsepower rating of the 645F for marine, these two engine models are very similar structurally, although the turbocharger on the 645F was a much more conventional design than the variation on the 645E3A. Back in the 1960s when the SD45 came out with the 20 cylinder 645E engine at 3600 horsepower the comparable marine engine was rated at 3500 horsepower.

[Allen Hazen]

mxdata--
Thanks for your (typically informative!) reply!
Preston Cook, in the "R&R" article cited, mentions the non-standard turbocharger on the SD45X. (It had a quill drive (shades of electric locomotive technology!) instead of the simpler sort of mechanical connection normal EMD turbochargers used in the lower power settings: better to insulate the turbo from engine vibration, I think.
Are the engines run at lower r.p.m. in marine service than in locomotive? Or is there some other reason for the lower power rating?

[mxdata]

Marine engines have very low auxiliary load compared to a locomotive installation, so you might at first think that they could be rated higher than a comparable locomotive engine. However, they have to contend with sea conditions, and the usual practice is to run a slightly lower rating in marine service than what you allow for railroad or power generating applications. This covers the situation where a tug may be running on a tow with a following sea and burying the stern, which usually is an overload condition for the engines. If you take the gross horsepower produced by a railroad engine (power for traction plus the power used by the auxiliary systems) and subtract 10% from that rating, you come out pretty close to most of the marine ratings. Also, marine engines are not necessarily all rated at the same RPM, it was very common for EMD to publish load curves for 900RPM and 800RPM maximum speeds for the same engine. The lower RPM was usually published for re-engining situations where the new engine would be installed with an existing reduction gear from an earlier (slower) engine.

Folks who do not like us discussing marine engines in this forum please accept my apology in advance.