• C420 and Rs-11

  • 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 mirrodie
Hi. I'm not new to this hobby but have a question about the C420 and RS11. They are from the same company but what made them different?

I know, for example, the difference between a 737, 767 and 757, but could not tell you the real difference between a 737-300, 737-500 and 737-600. But I know subtle differences exist.

So what was really different about those 2 engines? And to the untrained eye, were they glaring or subtle differences?
  by Allen Hazen
The basic difference is ... 7 years. The RS-11 was introduced in 1956, with a 12-cylinder, 1800 hp diesel engine. The C420 was the modernized version introduced in 1963, with an improved, 2000 hp, version of the same basic engine. (GE 752 traction motors and GE GT581 generator being standard on both models.)

Technically, the biggest change in the C420 was a centralized air filtration system, analogous to those on EMD's GP30 and GE's U25B. This is reflected visually: the RS-11 has a row of square ventilation openings (sometimes covered with louvers, sometimes not) along its long hood, just below the roof. The C420 has one large intake just behind the cab, and then plain sides until you get close to the radiator end of the hood.

Cosmetically, the RS-11 has notches in the corners of its hoods (where the number boards and the sandbox fills are): the C420 has much shallower notches at the end of the long hood (and the short hood on high-short-hood units), and the low-nose versions have notchless noses.

To confuse you more, there are several related models. The RS-32 and RS-36, built in 1961-1963, are very similar in appearance to the RS-11, and almost identical in appearance to each other. (The square vents on the hood sides are grouped into two groups of three rather than evenly space along the hood as on the RS-11: otherwise visible differences are very subtle things like the precise shape of the lifting pads.) The RS-32 had the uprated, 2000 hp, engine used in C420. (Alco had two different systems of model numbering. RS-11 and RS-36 are also known as Dl-701; RS-32 and C420 as Dl-721 and Dl-721A.) I think Alco's idea was that the RS-32 would replace the RS-11, but some railroads wanted lower-power units, and the RS-36 was an 1800hp version (but with some electronic refinements in common with the RS-32). (Norfolk & Western rostered RS-11, RS-36 and C420, so the N&W locomotive photos a George Elwood's marvelous site, http://rr-fallenflags.org/ , might be a good place to practice learning to spot the differences.)

Finally, Alco's Canadian subsidiary MLW produced two similar models, the RS-10 and RS-18. The RS-18 was, internally, virtually the same as an RS-11, but has notchless corners to its hoods: I recently mistook a low-nose RS-18 for a C420 in a photo, though if you look carefully they are easy enough to distinguish. (RS-18 production lasted into the mid 1960s; late RS-18 have the hood-side vents grouped as on the RS-32/36.) The RS-10, produced for a few years in the mid 1950s, had a carbody similar to that of an RS-18, but used the earlier model, 1600 hp, engine used in the RS-3.

I hope that's more helpful than confusing!
  by scottychaos
Im experiencing de'ja vu! ;)
We had this same question a few years ago..here is the old thread:

http://www.railroad.net/forums/viewtopi ... =4&t=21515

I will just re-post my reply from that thread here!

The rear grills look quite different..
the C420 has a smooth "century style" air intake at the rear of the longhood, same style as the other centuries.

the RS11 has an intake that takes up more of the carbody, and grills that stick out from the carbody side, not smooth..
the century has a nice, neat smooth long hood side..no bulging grills like the RS11.

the RS11 also has the round fan on the rear of the roof..again similar to the older RS3 style..the Century has no round fan on the roof.

The nose notches are also different..
the RS11 has "RS11 style notches" and the Cenury has "Century style notches"! ;)
The RS11 notches are much "deeper" than the Century notches.
the RS11 often (but not always) has sand plugs on the notches, the Century does not.

after awhile you will be able to easily tell a RS11 from a high-hood C420 at a glance.
they each have a distincive "overall look" that is easy to spot once you are familiar with them..
much like telling the difference between a 1965 and 1967 Ford Mustang..
the differences are clear and obvious once you know what they are..

the C420 is also a much more massive-looking engine than the RS11..
it just "looks" like a Century..while the RS11 looks like...a RS11! ;)


Both models can be found in high-hood and low-hood (nose) versions..
For the RS11 the high hood is much more common than the low hood.
and for the C420, the low hood is much more common that the high hood!

  by MEC407
mirrodie wrote:I know, for example, the difference between a 737, 767 and 757, but could not tell you the real difference between a 737-300, 737-500 and 737-600. But I know subtle differences exist.
Since Allen and Scot did a great job of answering your C420/RS-11 question, I'll take a quick stab at your 737 question. :wink:

737-300: first flew in 1984; 109 feet 7 inches long; seats a maximum of 149 people.

737-500: first flew in 1989; 101 feet 8 inches long; seats a maximum of 132 people; replacement for the 737-200.

737-600: first flew in 1998; 102 feet 6 inches long; seats a maximum of 130 people; replacement for the 737-500.
  by Eliphaz
The Century series also introduced the V fronted two-window cab, on low nose units. the RS series all had single window flat fronted cabs.

The cab position of the C-420 is distinctly farther back than the RS-11, I think, and I have the feeling, being too lazy to go 'look it up', that the RS-32 cab was farther forward than either.
  by Allen Hazen
I'm also too lazy to go and check, but I think the cab is in about the same position on the RS-11/RS-32/RS-36. I suspect you are confusing the RS-32 with the RS-27.

The RS-27 (built 1959-1963) being the predecessor of the the C424, related to it about the way the RS-32 is related to the C420. Visually, it looks like a low-nose RS-11/RS-32/RS-36, but with the cab moved forward, leaving a very short, snub-nose, short hood. Over-all length similar: long hood longer because the RS-27 and C424 had the 16-cylinder, 2400 hp, version of the engine instead of the 12-cylinder, 1800/2000 hp version.

The cab may be a tiny bit further back (so, the short hood a bit longer) on the C420 than on the earlier 12-cylinder models. Alco wanted to market the C420 for optional passenger use, and so designed it with a large short-hood to accommodate a steam generator. The C420 is actually a bit longer, overall, than the C424, i.i.r.c.: the C424 was designed as the smallest (so cheapest to build) possible freight locomotive with the 16-cylinder engine, and the C420 was given more generous dimensions to allow it to be adapted for passenger use: or so I recall from the "Railroad Model Craftsman" articles on these models in the 1980s.

(Thanks for mentioning the V-shaped cab front on the C420: it is a noticeable difference from the (low-nose versions of) the earlier models. Including the low-nose RS-18: I really SHOULDN'T have confused that with a C420!)
  by cdw
The C420 is an easier unit to work on. For example the primary and secondary fuel filters, oil filters and oil cooler are all located in the same area ,on the RS11 the oil filters and oil cooler are located in the fan compartment which is cramped.The hood is designed different on a 420 to allow additional room for power assembly change out. the radiators are overhead in the fan room. This allows the use of fail safe shutters in place of air operated shutters. On a 420 The engine air filters are easyer to service,and if bag filters are installed it is actualy a pleasure! On a 420 the compressor is in the fan room with more access area to work on it and align it. The air equipment is more accessable on the 420 to allow for change out. In my opinion the C420 is easyer to maintain than the RS11.
Dick Welles