Class K-55 (Locobase 7231) 
Data from RI to 1951Locomotive Diagrams Combined supplied in May 2005 by Allen Stanley from his extensive collection.
As part of the USRA's distribution of Mikados, Baldwin built the first 9 of the Rock Island's batch of 20 and Alco produced the latter 11. Locobase has several examples of as-built light Mikes, so this entry shows the Rock's firebox reconditioning in which 28 sq ft of arch tubes was replaced by 77 sq ft of thermic syphons.
Class K-60 (Locobase 2796)
The first of the Rock's Mikados, these engines were built in the following batches:
Numbers Builder Date Valve gear
2500-2539 Baldwin 1912 Baker
2540-2549 Alco 1912 Walschaerts
2550-2574 Baldwin 1913 Baker
2575-2594 Alco 1918 Walschaerts
48 more followed after World War I.
Piston valves were of a generous 16" diameter and the engines were delivered with brick arches and 29 sq ft of arch tubes. WJ Tollerton, Chief Mechanical Superintendent said in Railway Age (9 January 1914) that they'd proven to be "excellent steamers; there is experienced no difficulty in maintaining full boiler pressure at all times and the absence of black smoke at the stack is evidence of their boiler efficiency." Per 1000 gross ton miles on the Herington-Pratt, Kansas section (126 miles at a ruling grade of 0.8%), the Mikes dropped coal consumption from 96 lb to 66 lb compared to the earlier 2-8-0s while raising the average train load from 1,650 tons to 2,400 tons.
Tenders held either 16 tons of coal or 3,200 to 4,400 gallons of oil. Boiler pressure in these engines began at 180 psi; the earlier ones were raised to 190 psi and later engines were delivered at 200-210 psi. Many had firebox updates in which the arch tubes were replaced by 82 sq ft of thermic syphons, which increased direct heating surface to 361 sq ft. Some even received roller bearings.
Clearly a prized workhorse that soldiered on to the end of steam on the Rock.
Class K-64 (Locobase 7232)
Data from RI to 1951 Combined Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.
The Rock Island continued building after World War I a line of Mikados that it first procured in 1912, but wrought several important changes. Both the direct heating surface and the superheater surface areas were increased, the former being accomplished by including 116.7 sq ft thermic syphons and the later by increasing the number of flues. The postwar class of 48 can be further subdivided by the number of tubes and a consequent difference in evaporative heating surface. The first two batches, which arrived in 1920 and 1922, were as shown in the specs. The last 24 are depicted in Locobase 7233.
Class K-64 (Locobase 7233)
Data from RI to 1951 Combined Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.
As the run of Mikados described in Locobases 2796 and 7232 came to its conclusion in 1923, Brooks rang one more change on the boiler. Ten more tubes were deleted in favor of two more superheater flues, which resulted in a still higher percentage of superheater area in relation to overall heating surface. The firebox heating surface remained the same and still included 116.7 sq ft of thermic syphons.
Class K-64B (Locobase 11)
Data from 1930 Locomotive Cyclopedia and RI to 1951 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.
Firebox had thermic syphons. One of a series of Mikado classes built for the Rock Island before and after World War I. Boiler pressure was later raised to 215 psi and the class redesignated K-68B to signify the increased tractive effort. A 14,000-gallon tender added later put 237,600 lb on the rails.
Class K-67B (Locobase 7223)
Data from RI to 1951 Diagram Combined Books supplied in May 2005 by Allen Stanley from his extensive collection.
Firebox had 82 sq ft of thermic syphons. These were the last Mikados delivered to the Rock Island and differed from the K-64B from Brooks (Locobase 11) only in steam pressure and having 2 fewer boiler tubes.
