ALCO S-2 and S-4

Infobox Locomotive
name=ALCO S-2 and S-4


imagesize =250
powertype=Diesel-electric
builder=ALCO and MLW
gauge=RailGauge|ussg|lk=on
wheeldia=convert|40|in|m|3|abbr=on
aarwheels=B-B
builddate=S-2: April 1940 – June 1950
S-4: August 1950 – January 1961
totalproduction=S-2: 1502
S-4: 797
length=convert|45|ft|5 +3/4|in|m|2|abbr=on
width=convert|10|ft|0|in|m|2|abbr=on
height=convert|14|ft|6|in|m|2|abbr=on
poweroutput=convert|1000|hp|kW|0|abbr=on
primemover=Alco 539T
cylindercount=Straight 6
cylindersize=12 ½ × 13 in (318 × 330 mm)
displacement=convert|1595|cuin|l|abbr=on|lk=on per cylinder
convert|9572|cuin|l|abbr=on total
aspiration=Turbocharged
enginetype=Four-stroke dieselThe ALCO S2 and S4 were convert|1000|hp|kW|0 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.

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.

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.

References

*
* Toppan, Andrew et al. " [http://www.thedieselshop.us/Alco_S2.HTML Alco/MLW S-2 Roster] ". Retrieved on December 29, 2005.
* Toppan, Andrew et al. " [http://www.thedieselshop.us/Alco_S4.HTML Alco/MLW S-4 Roster] ". Retrieved on December 29, 2005.