ALCO DH643

4 ft 8+1⁄2 in (1,435 mm)Length75 ft 10 in (23.11 m)Loco weight378,000 lb (171,000 kg)Prime moverAlco 251C, (x 2)Engine typeV12 Four-stroke diesel, (x 2)AspirationTurbochargerDisplacement8,016 cu in (131.36 L)Cylinders12 (x 2)Cylinder size9 by 10+1⁄2 inches (229 mm × 267 mm)TransmissionVoith hydraulicLoco brakeStraight airTrain brakesAir

Performance figures
Maximum speed	77 mph (124 km/h)
Power output	4,300 hp (3,200 kW)
Tractive effort	95,000 lbf (422.58 kN)

Career
Operators	Southern Pacific Railroad
Numbers	9018–9020 (later 9150–9152; final 9800-9802)
Locale	North America
Scrapped	1973

The ALCO C-643DH, also known as the Century 643DH, was a twin-engine diesel-hydraulic locomotive, the first diesel-hydraulic road switcher built in the United States. It had a C-C wheel arrangement and generated 4,300 horsepower (3,200 kW). Only three were built, all for Southern Pacific Railroad in 1964 (#9018–#9020). The Alco C-643DHs joined 21 Krauss-Maffei ML-4000 diesel-hydraulics already on the Southern Pacific's roster. They spent most of their service lives in the flat San Joaquin Valley in California.

Dissatisfaction over the poor performance of diesel-hydraulic locomotives, as well as their use of foreign-made components (the hydraulic transmission was of German Voith design), eventually led Southern Pacific to sell the 3 C-643DHs for scrap in 1973. None of the 3 examples built survived into preservation.

Original owners

Railroad	Quantity	Road numbers	Notes
Southern Pacific Railroad	3	9018–9020	renumbered 9150–9152

See also

• List of ALCO diesel locomotives
• ALCO Century 855

References

• "ALCO 244 and 251 Diesel Engines". Pacific Southwest Railway Museum. Archived from the original on 13 January 2006. Retrieved 20 February 2006.
• Kirkland, John F. (1989). The Diesel Builders, Volume Two: American Locomotive Company and Montreal Locomotive Works. Interurban Press, Glendale, CA. ISBN 0-916374-81-5.
• Pinkepank, Jerry A. (1973). The Second Diesel Spotter's Guide. Kalmbach Publishing Co., Milwaukee, WI. ISBN 0-89024-026-4.
• Strapac, Joseph A. (1993). Southern Pacific Historic Diesels, Volume 2: Diesel-Hydraulic Locomotives. Shade Tree Books, Bellflower, CA. ISBN 0-930742-15-X.
• Strapac, Joseph A. (2001). Southern Pacific Historic Diesels, Volume 8: Alco Roadswitcher Locomotives. Shade Tree Books, Bellflower, CA. ISBN 0-930742-23-0.

External links

• Alco Six-Axle Centuries Roster
• Southern Pacific DH-643