Missouri-Kansas-Texas 4-6-2 "Pacific" Locomotives in the USA

Class H-1 (Locobase 7081)

Data from MKT 1941 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 48425-48434 in October 1910.

The first of the Alcos for the Katy, these arrived with superheaters. They had 12" (305 mm) diameter piston valves with 1 1/16" (27 mm) lap, 1/4" (6.3 mm) lead, 6" (152 mm) total travel. Firebox heating surface area included three arch tubes that contributed 27 sq ft (2.51 sq m) in area. By the early 1920s four of the class (360-361 and 365-366) had been converted to oil burning.

The next ten (Locobase 7080) introduced larger cylinders and all used oil fuel.

Class H-2a (Locobase 7080)

Data from MKT 1941 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 50188-50194 in 1911.

Following the H-1s (Locobase 7081) by a year, these Katy H-2a had 14" (356 mm) diameter piston valves with 1 1/8" (28 mm) lap, 1/4" lead (6.3 mm), 6 1/2" (165 mm) total travel. This resulted in a useful increase in power while the boiler and grate remained essentially unchanged.

Firebox heating surface area included three arch tubes that contributed 30 sq ft (2.79 sq m) in area.

Class H-2b (Locobase 7082)

Data from MKT 1921 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 51871-51880 in 1912.

Following the H-2as (Locobase 7080), the H-2bs repeated the basic design while enlarging the boiler constituents by 20 tubes and 4 superheater flues.

As in the H-2as, firebox heating surface area included three arch tubes that contributed 30 sq ft (2.79 sq m) in area. By the early '20s, engines 371-374 burned oil.

All remained in service until 1949-1950.

Class H-3a (Locobase 5462)

Data from MKT 1941 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

These were express Pacifics for the Katy supplied in two batches by Alco - 5 in each of 1915 & 1916. By 1941, all but two had Baker gear -- 377, 385 had Walschaert gear. As with the H-2bs, these had 14" diameter piston valves with 1 1/8" lap, 1/4" lead, 6 1/2" total travel.

Compared to the H-2s, however, the larger H-3b fireboxes used four arch tubes (vice 3 in earlier classes) that contributed 45 sq m (4.18 sq m) to the firebox heating surface area. Tube count grew by 31 and superheater flues increased to 36.

Class H-3d (Locobase 7084)

Data from MKT 1941 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 6477-6481 in April 1923.

Other than deleting five boiler tubes from the H-3's total, these Limas were virtually identical to the earlier locomotives. Some of these Pacifics were later fitted with Boxpok drivers and slotted-steel pilot, but the basic dimensions remained the same.

Class K/H-3b, 3c (Locobase 7083)

Data from MKT 1941 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Alco's Schenectady Works delivered the first ten in 1917, works numbers were 57531-57540 in 1917. Lima followed with ten more in 1920; works numbers were 5960-5969 in September 1920.

Following the H-3a by a couple of years, these express Pacifics had slightly higher boiler pressure and thus more tractive effort. They were otherwise essentially identical to the H-3a. All used 14" (356 mm) piston valves to supply steam to the cylinders. The Limas arrived with cast trailing trucks and the others received theirs during updates.

All served the Katy for thirty years or longer. before being retired in 1949 and into the 1950s.