New Zealand Government Railways 4-8-0 Locomotives in New_Zealand

Class B (Locobase 9568)

Data from Howell, Comparative Statistics of the Australasian Railways, Journal of the Royal Statistical Society, March 1899, pp. 98-99 and John Garner's [], last accessed 7 September 2008.

Sharp, Stewart of Glasgow contributed four (works #4508-4511) in 1899 and the NZR's own Addington shops built six (works #24, 26, 43, 54-56 in 1899 to 1903) of these sizable Twelve-wheelers. Garner's comment about their design summarizes what one can tell from the specs and from a photograph: "Mechanically the 'B' was years ahead of its time, with a new simple design of piston valve and a modified Walschaerts [sic] valve gear. For their time the 'B's were powerful brutes and rated to haul 600 ton goods trains on easy grades, and could handle 220 tons over the steep grades north of Dunedin."

They were obviously worth retaining and most put in six decades of service, although three of the four Sharp, Stewart locomotives were converted to 4-6-4T class We in 1902 (see Locobase 5189). Four were later refitted with a new boiler fitted with a wide firebox over a eighteen-year period.

Class Ba (Locobase 5164)

Data from John Garner's comprehensive site at [] ... (October 2002); and [] (visited 21 May 2004); D[ennis] Rock Carling, 4-8-0 Tender Locomotives (New York: Drake Publishers, Inc, 1972), p. 81 and serial 231 on table XIII [13], pp.106-107.

A rare narrow-gauge Twelve-wheeler, these locomotives were intended for heavy freight work at speeds no greater than 30 mph (48 kph). Garner notes, however, that they also hauled passenger trains in the Otago area.

Of the 10, two were rebuilt in 1928 with larger fireboxes and boilers to raise steaming capacity to main-line requirements. notes that this was a substantial effort. The boiler's centerline was raised from 6' 3" (1.9 m) to 7' 4" (2.23 m), the grate area enlarged to 26.4 sq ft (2.45 sq m), and pressure raised to 200 psi (14.06 bar). Tractive effort climbed to 21,200 lb (9,616 kg).

Obviously, this was not an urgent requirement as the other three to be made over were only modified in 1948-1949. Rated to haul 700-750 tons on the level, a wide-firebox Ba could surmount the notorious Mihiwaka Bank (north of Dunedin) with 270 tons, 50 tons better than one of the other members of the class fitted with a narrow-firebox boiler

Class Bb (Locobase 5165)

Data from John Garner's comprehensive site at [] ... (October 2002). See also "New Engines for the New Zealand Government Rys", Locomotive Magazine, Volume XXIII [23] (15 February 1917), p. 20.

An obvious follow-on class to the Bas (Locobase 5164) with cylinders 1" (25.4 mm) larger in diameter, these 12-wheelers had the same small boilers and low factor of adhesion. Garner says that 10 of these engines were given shunting duties, where they were quite successful. That success led to the conversion of the entire class between 1932 and 1938.