Alco C636 (Century 636): Specs, Production Roster & History

Last revised: August 26, 2026

The Alco Century 636 (C636) was the most powerful single-engine diesel-electric the American Locomotive Company cataloged for domestic sale: a six-axle, 3,600-horsepower road-switcher built around the turbocharged 16-251F and Alco’s new Hi-Ad trucks. Schenectady outshopped 34 between December 1967 and November 1968. Only three U.S. railroads bought production units—Spokane, Portland & Seattle (10), Penn Central (15, a Pennsylvania Railroad order delivered after the February 1, 1968 merger), and Illinois Central (6)—plus three expensive factory demonstrators that never sold a follow-on order.

Licensee A.E. Goodwin in Australia built another 35 C636s for Pilbara iron-ore roads (1968–72), for a worldwide C636 total of 69. Montreal Locomotive Works later built the related but separate M636 (111 at Montreal, plus Australian M-line copies). One unrebuilt Schenectady C636 still earns its keep: Delaware-Lackawanna #3642 at Scranton, photographed in service as recently as November 2025.

Illinois Central publicity photo pair of new C636s with a coal drag on the Kentucky Division summer 1968

An Illinois Central publicity photo featuring a pair of its new C-636s, #1101 and #1102, posed swinging off a coal spur at Grand Rivers, Kentucky in the summer of 1968. The six IC C636s (1100–1105) were assigned to the Kentucky Division and kept close to the Paducah shops because of reliability issues; they regularly worked coal trains in this territory. They were retired in 1979. American-Rails.com collection.

On this page: At a glance · In the Century catalog · Design · Why it sold so few · U.S. owners · The three demonstrators · Data sheet · Production rosters · M636, related not identical · What still runs

At a Glance

Item	Detail
Builder	American Locomotive Company, Schenectady, N.Y. (licensee: A.E. Goodwin, Australia)
Model	Century 636 (C636); specification DL636
Type	Six-axle (C-C) diesel-electric road-switcher
Horsepower	3,600 hp
Prime mover	Alco 16-251F (V-16), turbocharged, 1,100 rpm
Schenectady production	December 21, 1967 – November 21, 1968
Alco-built total	34 (3 demonstrators + 31 railroad units)
U.S. railroad buyers	SP&S 10, Penn Central 15, Illinois Central 6
First production	Spokane, Portland & Seattle #330–335 (December 1967; #331 dated December 21)
Last Alco C636s	SP&S #340–343 and demonstrators 636-1/2/3 (November 1968)
A.E. Goodwin C636s	35 for Hamersley Iron, Mt. Newman Mining, and Cliffs Robe River (1968–72)
Worldwide C636 total	69
Related MLW model	M636 (111 built at Montreal, 1969–75)—not a C636
Predecessor in line	C630 (3,000 hp, 16-251E)
Electrical	GE GTA-11 main generator (AC); six GE 752 traction motors
Last unrebuilt Alco C636	Delaware-Lackawanna #3642 (ex-Penn Central 6342), Scranton, Pa.

Where the C636 Fit in Alco’s Catalog

Alco launched the Century line in 1963 to replace the RS/RSD road-switchers after the mixed reputation of the 244-series engine years. Six-axle Centuries stepped up in a straight horsepower ladder: the C628 (2,750 hp, 16-251C, 1963), the C630 (3,000 hp, 16-251E, 1965), then the C636 at 3,600 hp. The naming was the usual Century code: C for Century, 6 for six axles, 36 for the 3,600-horsepower rating.

Visually the C636 is a C630 with a different intercooler box. The C630 has two grilles stacked on the box behind the cab; the C636 keeps only the upper grille. Both ride Alco Hi-Ad (high-adhesion) three-axle trucks rather than the older Trimounts of early C628s. Length between coupler pulling faces is the six-axle Century standard, 69 feet 6 inches.

The 3,600 hp rating put the C636 against Electro-Motive’s SD45 (20-cylinder 645, 3,600 hp, in production since 1965) and General Electric’s emerging U33C/U36C. EMD built more than 1,200 SD45s through 1971 while GE outshopped nearly 600 U33Cs and U36Cs. Alco simply did not get the orders.

The C636 was builder's last six-axle Century from Schenectady although not the final Alco locomotive ever built. After the November 1968 C636s, the plant still finished C415s and, in January 1969, Newburgh & South Shore T-6 switchers #1016 and #1017—the last units out the door.

Design

Under the hood sat Alco’s last high-output 251 variant, the 16-251F: four-cycle, 9-inch bore, 10½-inch stroke, turbocharged, rated 3,600 hp at 1,100 rpm. Some secondary sheets still print “251E” on the C636. The 251E is the 3,000 hp engine in the C630 and C430. The 3,600 hp jump is the 251F.

Electrical gear remained General Electric even though GE had been a full locomotive competitor since the U25B of 1959. The C636 used a GTA-11 AC main generator and six GE 752 traction motors. Dynamic braking was optional. Illinois Central’s six were built without it. Gear ratios in Alco-oriented tables used on this site are 81:22 (about 75 mph) and 77:26 (about 93 mph). Other mechanical summaries list the more common six-axle freight 74:18. Treat those as catalog options, not a single fleet standard.

Published weight is the item that used to overstate the case. Alco listed about 372,000 pounds with optional ballast up to 420,000 pounds. Heavy ore and some Australian units sat at the high end. A typical EMD SD40 of the period was in the high 360,000s to about 390,000 depending on ballast; an SD45 was in the same neighborhood. The C636 could be a heavy locomotive. It was not uniquely 420,000 pounds in every application, and it did not uniquely destroy track. What railroads did dislike, from the earlier C628/C630 onward, was Alco’s combination of high axle loading, Hi-Ad geometry, and a builder already on thin ice for reliability and parts.

Starting tractive effort on the Jean-Denis Bachand / Railroad Model Craftsman-style sheet is about 81,150 pounds at 25 percent adhesion. The olderdata sheet on this page listed 100,000 pounds at 7 mph. Those are different ratings (starting vs. a continuous/speed point). Both appear below so a reader can see the published range rather than a single rounded claim.

American Locomotive builder photograph of new Illinois Central C636 1100 at Schenectady New York May 1968

An American Locomotive builder's photo featuring new Illinois Central C636 #1100 in May, 1968 at Schenectady, New York.

Why It Sold So Few

Alco spent on the order of $5.5 million to build three demonstrators—636-1, 636-2, and 636-3—completed in November 1968, after most of the production run had already been delivered. The set was meant to tour Class I railroads and close the sale that the catalog had not. It did the opposite. Demonstrator 636-2 was the unit that actually went out. On a Santa Fe evaluation the same traction-motor blower failed and was replaced on three of four runs; the prime mover would shut down with it. Southern Pacific’s test was no better. Railfan & Railroad later called the C636 Alco’s “most notorious failure” of the late Century years: a 3,600 hp advertisement for how far build quality had slipped.

Alco's blower problem was real; it was not a 244-engine hangover. The 251F was a different machine from the 244s of the late 1940s and 1950s. What the 244 (and to a lesser extent the 539) had already done was spend Alco’s reputation. Mechanical departments that remembered early 244 crankshafts and turbo lag did not give the 251 a clean sheet, even when the later engine was the better product.

Two market facts finished the model. First, Alco was still buying its electrical cabinet from the company that was now its rival. GE’s own six-axle Universals were on the same bid lists. Second, EMD already had a 3,600 hp six-axle locomotive that worked. Railroads that wanted that horsepower bought SD45s in fleet numbers. Penn Central’s fifteen C636s arrived because the Pennsylvania Railroad had already been an Alco six-axle customer (C628, C630) and had the order in before the merger. Illinois Central wanted coal-drag horsepower on the Kentucky Division. SP&S, always Alco-friendly in the Pacific Northwest, took ten. Nobody else in the United States signed.

Alco announced it would leave the locomotive business as 1968 ended. U.S. diesel deliveries that year had fallen below 1,000 in a market that had once seen 4,500. The C636 did not cause the shutdown by itself. It was the last high-horsepower pitch from a builder that had already lost the argument.

Penn Central Alco C636 6339 at Buffalo New York April 3 1972 Warren Calloway collection

One of Penn Central's huge C636s, #6339, at Buffalo, New York on April 3, 1972. Warren Calloway collection.

U.S. Owners

Spokane, Portland & Seattle (10)

SP&S took the first production C636s: #330–335 in December 1967 (builder numbers S-3488-01 through -06) and #340–343 in November 1968 (S-6010-01 through -04). They were Northwest forest and drag power on a road that had bought Alco six-axles for years. At the March 1970 Burlington Northern merger they became BN #4360–4369. BN retired the group around 1980. None are known to survive.

Penn Central (15)

The Pennsylvania Railroad ordered fifteen C636s as the next step after its C628s (#6300–6314) and C630s (#6315–6329). Delivery was March–April 1968, after February 1, so they were lettered Penn Central #6330–6344 (S-3499-01 through -15) from new. PC put them on heavy freight, including Appalachian coal. Conrail inherited them as #6780–6794. Most were off the roster in the early 1980s. One unit, PC #6342 / CR #6792, went to Delta Terminal as #1001, then to Delaware-Lackawanna, where it still runs as #3642.

Illinois Central (6)

#1100–1105 (S-6000-01 through -06), May 1968, were coal power on the Kentucky Division. They had no dynamic brakes. They became Illinois Central Gulf engines at the 1972 GM&O merger, same numbers, and were retired about 1979. All six were later scrapped (reports put the cuts in the early 1980s after a pass through used-power dealers such as PNCX). No IC C636 survives.

The Three Demonstrators

636-1, 636-2, and 636-3 (S-6008-01 through -03) were completed in November 1968. After the failed Class I tour they were sold to Morrison-Knudsen as 5401–5403. MK used them as contractor power: Libby Dam construction in Montana, a period on Pacific Great Eastern, Black Mesa & Lake Powell construction in Arizona, and a well-photographed lease to the Clinchfield at Erwin, Tennessee, in November 1971 during a CRR power shortage. In 1973–74 they went to Québec Cartier Mining as #77–79 and spent years on heavy ore trains in Quebec.

Cartier later disposed of them. 5401 / QCM 79 was reported scrapped in 2002 after a crankshaft failure. The other two passed through New York, Susquehanna & Western and Western New York & Pennsylvania; both of those Alco-built C636s have been cut up. They are not the M636s still moving on Genesee Valley Transportation properties.

Morrison-Knudsen C636 #5401 (formerly demonstrator 636-1) at Erwin, Tennessee in November, 1971

Morrison-Knudsen C636 #5401 (formerly demonstrator 636-1) is seen here on the Clinchfield at Erwin, Tennessee in November, 1971. The CRR was leasing the unit during a power shortage. MK wound up purchasing all three demonstrators, which were later sold to Cartier Mining. Warren Calloway photo.

Data Sheet and Specifications

Figures below follow the Kirkland-era American-Rails compilation long used on this page, with the engine letter corrected to 251F and weight expressed as the catalog range rather than a single 420,000-pound figure. Alternate mechanical-digest numbers are noted underneath.

Specification	Value
Entered production	December 21, 1967 (Spokane, Portland & Seattle #331)
Years produced (Alco)	December 21, 1967 – November 21, 1968
Model specification	DL636
Engine	Alco 16-251F, V-16 (some secondary sheets still print 251E; 3,600 hp is the F rating)
Horsepower	3,600
Engine speed (rated)	1,100 rpm
Carbody	Alco Century road-switcher
Length (coupler pulling faces)	69 ft 6 in
Weight	372,000 lbs catalog; optional ballast to 420,000 lbs
Dynamic brakes	Optional (IC built without)
Trucks	C-C
Truck type	Alco Hi-Ad (high adhesion)
Truck wheelbase	12 ft 6 in
Wheel diameter	40 in
Traction motors	GE 752 (6)
Main generator	GE GTA-11 (AC)
Gear ratio (as listed this site)	81:22 (75 mph), 77:26 (93 mph)
Tractive effort (as listed this site)	100,000 lbs at 7 mph
Top speed (as listed this site)	93 mph

Alternate published package (Diesel Shop / RMC-style summaries, often mixed with later M636 geometry): 74:18 gearing, ~65 mph, starting TE about 81,150 lbs at 25% adhesion, continuous about 79,500 lbs at 12 mph, fuel ~3,200 gallons, Westinghouse 26L brake. Some of those dimensional lines (13 ft 7 in truck wheelbase, Dofasco trucks) describe the Montreal M636, not the Schenectady C636. Prefer a builder order sheet or railroad diagram when documenting a specific unit.

Production Rosters

Alco, Schenectady

Total built = 34

Owner	Road number(s)	Construction numbers	Completion	Notes
Spokane, Portland & Seattle	330–335	S-3488-01 thru S-3488-06	December 1967	First production; to BN 4360–4365
Penn Central	6330–6344	S-3499-01 thru S-3499-15	March–April 1968	PRR order; to Conrail 6780–6794. PC 6342 survives as DL 3642
Illinois Central	1100–1105	S-6000-01 thru S-6000-06	May 1968	No dynamic brakes; all later scrapped
Alco (demonstrators)	636-1, 636-2, 636-3	S-6008-01 thru S-6008-03	November 1968	To Morrison-Knudsen 5401–5403; then Cartier 77–79. All subsequently scrapped
Spokane, Portland & Seattle	340–343	S-6010-01 thru S-6010-04	November 1968	Last railroad C636s from Schenectady; to BN 4366–4369

Owner totals: SP&S 10, Penn Central 15, Illinois Central 6, Alco 3 = 34. Serial blocks and months match Extra 2200 South / Diesel Shop / Kirkland-style lists used on this site.

A.E. Goodwin, Australia

Goodwin built C636s under license for three Pilbara iron-ore operators. As-delivered numbers below follow Extra 2200 South. Hamersley units are often later cited in the 3000 series after renumbering; the table keeps the as-built 2006–2017 block. Robe River’s first five were constructed for Bechtel as 262.001–262.005; Mt. Newman’s 5452–5456 were Bechtel 100.0001–100.0005.

Total built = 35

Owner	Road number(s)	Construction numbers	Completion
Hamersley Iron	2006–2007	G-6011-01 thru G-6011-02	April 1968
Hamersley Iron	2008–2011	G-6014-01 thru G-6014-04	December 1968
Hamersley Iron	2012	G-6028-01	July 1969
Mt. Newman Mining	5457–5459	G-6027-01 thru G-6027-03	June–August 1969
Mt. Newman Mining	5460–5464	G-6035-01 thru G-6035-05	December 1969–April 1970
Hamersley Iron	2013	G-6040-01	July 1970
Mt. Newman Mining	5465–5468	G-6041-01 thru G-6041-04	July–August 1970
Hamersley Iron	2014–2017	G-6043-01 thru G-6043-04	October–November 1970
Cliffs Robe River Iron Associates	262.001–262.005	G-6060-01 thru G-6060-05	February 1971
Cliffs Robe River Iron Associates	1715	G-6060-06	February 1972
Mt. Newman Mining	5452–5456	G-6012-01 thru G-6012-05	June 1972

Hamersley 12 + Mt. Newman 17 + Robe River 6 = 35. Wikipedia’s older “29 Australian C636s” omits the Robe River six. Goodwin and later Comeng also built M636 copies for the same mines; those are not C636s and are not in this table.

M636: Related, Not Identical

Montreal Locomotive Works introduced the M636 in 1969, after Schenectady had stopped. It is the C636’s Canadian successor: still 3,600 hp and a 16-251F, but riding Dofasco trucks instead of Alco Hi-Ads, with the M-line carbody refinements MLW had already applied to the M630. British Columbia Railway later took wide-cab M630s; the M636s for CN and CP were conventional cabs. CN’s forty were ordered without dynamic brakes.

Montreal production, from Extra 2200 South / Diesel Shop:

Owner	Road number(s)	Qty	Construction numbers	Completion
Canadian Pacific	4700–4728	29	M6031-01 thru M6031-29	November 1969–October 1970
Canadian National	2300–2319	20	M6037-01 thru M6037-20	April–September 1970
Canadian Pacific	4729–4743	15	M6038-01 thru M6038-15	October–December 1970
Canadian National	2320–2339	20	M6052-01 thru M6052-20	January–April 1971
Québec Cartier Mining	71–73	3	M6058-01 thru M6058-03	January 1972
Ferrocarril del Pacífico	651–658	8	M6062-01 thru M6062-08	June 1972
Québec Cartier Mining	74–76	3	M6072-01 thru M6072-03	October 1973
Ferrocarril del Pacífico	659–666	8	M6073-01 thru M6073-08	December 1973
Québec Cartier Mining	81–85	5	M6085-01 thru M6085-05	March 1975

Montreal M636 total = 111 (CP 44 + CN 40 + Cartier 11 + Ferrocarril del Pacífico 16). The older roster on this page listed only the first CN twenty and the CP 4700s, misspelled the Mexican road as “Ferrocaril del Pacfico,” and then added C636 + M636 into an “83 units” total that does not match either model. CP also took one M640 (#4744, 4,000 hp, 18-251F) in March 1971—the only M640, not a C636.

Cartier later bought used CN M636s. Those ore-haulers, plus CP 4743, are why M636s still appear on U.S. short lines next to DL’s one remaining C636. They are cousins, not the same locomotive.

What Still Runs

As of 2025–26 the only unrebuilt Alco-built C636 in existence is Genesee Valley Transportation’s Delaware-Lackawanna #3642 (Alco 3499-13, April 1968, nee PC 6342). It works the Pocono grades out of Scranton with GVT’s MLW M630s and M636s. RailPictures and roster sites logged it on PO75 and Taylor Yard transfers as recently as November 2025. Diesel Shop’s Delaware-Lackawanna list, revised July 22, 2026, still carries 3642 as active.

Legacy

The C636 is Alco’s last high-horsepower argument in a market that had already chosen EMD and GE. Thirty-four units from Schenectady, thirty-five more from Goodwin, and a much larger Montreal M636 afterlife. The U.S. story is three railroads, a failed demonstrator tour, and one locomotive still climbing out of the Lackawanna valley. That is a thinner commercial record than the 2008 copy implied, and a clearer one.

Sources

Kirkland, John F. The Diesel Builders, Volume Two: American Locomotive Company and Montreal Locomotive Works. Glendale: Interurban Press, 1989. (Production/specification tradition for this page; Australian C636s are Goodwin, not the three Schenectady demonstrators.)
Solomon, Brian. Alco Locomotives. Minneapolis: Voyageur Press, 2009.
Foster, Gerald. A Field Guide to Trains. New York: Houghton Mifflin, 1996.
Pinkepank, Jerry A. Diesel Spotter’s Guide. Milwaukee: Kalmbach, 1967. (Too early for C636 production; useful for Century context only.)
The Diesel Shop, Alco C636 / A.E. Goodwin and MLW M630/M636/M640 production rosters (Extra 2200 South tradition; updated lists)
Diesel Era staff, “Penn Central’s Alco C-636 and GE U33C” (PC/PRR order history)
TrainWeb / Old Time Trains, Alco demonstrator 636-1/2/3 to Morrison-Knudsen 5401–5403 and Cartier (North American construction-lease chain)
The Diesel Shop, Delaware-Lackawanna roster, revised July 22, 2026 (DL 3642 active)
Trains News Wire, Scott A. Hartley, August 20, 2023 (GVT six-motor purchases; WNY&P C636s already gone)

Production serials and owner totals are the Extra 2200 South / Kirkland compilation long used on American-Rails. Engine letter, demonstrator history, M636 counts, and 2026 survivors are corrected.