ALCO S-2 and S-4
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| Power type | Diesel-electric |
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| Builder | ALCO and MLW |
| Build date | S-2: April 1940 – June 1950 S-4: August 1950 – January 1961 |
| Total production | S-2: 1502 S-4: 797 |
| AAR wheel arr. | B-B |
| Gauge | 4 ft 8½ in (1,435 mm) |
| Length | 45 ft 5¾ in (13.86 m) |
| Width | 10 ft 0 in (3.05 m) |
| Height | 14 ft 6 in (4.42 m) |
| Prime mover | Alco 539T |
| Engine type | Four-stroke diesel |
| Aspiration | Turbocharged |
| Displacement | 1,595 cu in (26.14 l) per cylinder 9,572 cu in (156.86 l) total |
| Cylinders | Straight 6 |
| Cylinder size | 12 ½ × 13 in (318 × 330 mm) |
| Power output | 1,000 hp (746 kW) |
The ALCO S2 and S4 were 1,000 horsepower (746 kW) switcher diesel locomotives produced by ALCO and Canadian licensee Montreal Locomotive Works (MLW). Basically, the two locomotives differed only in trucks, with the S-2 using ALCO's own Blunt trucks, and the S-4 riding on standard AAR type A switcher trucks. Both were powered by ALCO 539 turbocharged, 6 cylinder diesels. The S-2 was built between April 1940 and June 1950, with a total of 1502 completed, while the S-4 was constructed between August 1950 and January 1961 (MLW until 1957) with total sales of 797. A modified version, the S-7, was built by MLW only; 29 were built between June and August 1957.
[edit] Identification
The S-2 and S-4 are distinguishable externally from the very similar S-1 and S-3 660 hp (490 kW) switchers in that they have a larger exhaust stack with an oblong base and a larger radiator shutter area on the nose sides. The S-1/S-3 radiator shutter area is taller than it is wide, while the S-2/S-4 radiator area is wider. The larger stack is due to turbocharging. The carbody and cab of late S-2s are nearly indistinguishable from those of S-4s. Hence, a truck swap can cause many to mis-identify a unit.
[edit] Survivors
A few S4s are still in service on shortline railroads around the United States. Several more are preserved in US and Canadian railroad museums.
Western Pacific 563, one of 2 S4s purchased by that railroad, is today preserved at the Western Pacific Railroad Museum at Portola, California.
[edit] References
- Pinkepank, Jerry A. (1973). The Second Diesel Spotter's Guide. Kalmbach Publishing Co., Milwaukee, WI. ISBN 0-89024-026-4.
- Toppan, Andrew et al. Alco/MLW S-2 Roster. Retrieved on December 29, 2005.
- Toppan, Andrew et al. Alco/MLW S-4 Roster. Retrieved on December 29, 2005.
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