New Zealand Government Railways 4-6-2 Locomotives in New_Zealand

Class Aa (Locobase 4962)

Data from [] accessed in January 2002. See also DeGolyer, Volume 63, pp. 187+. Works numbers were 41826-41835 in December 1914.

These appear to be the last Baldwin gasp before New Zealand began supplying most of its own locomotives as the Ab class that followed the next year. They all arrived in June 1915. Firebox heating surface area included 11.7 sq ft (1.1 sq m) of arch tubes. Piston valves measured 9 1/2" (240 mm) in diameter.

Retirements came in December 1955 (648, 652-655) and February 1957 (649-651, 656).

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Class Ab (Locobase 2489)

Data from John Garner and his website [] (October 2002). See also Brian Greenwood's Brian's Place website for the history of the Ab class at [], last accessed 25 August 2017; and See also S H Jenkinson, "The Future Development of the Locomotive in New Zealand", New Zealand Journal of Science and Technology, Volume 4, No 6 (January 1922), pp. 291-302.

Built in several groups over several years with 18 coming from the Addington shops,

20 more from New Zealand railway shops, and another 20 from A & G Price. (The most numerous contribution, which came from Glasgow's North British Locomotive Company, appears in Locobase 20282.)

OS Nock (RWC IV, pl 103) comments: "An infallible testimony to the excellency of their design was the freedom with which they attained speeds of around 60 mph ...despite coupled wheels no larger than 4' 6" in diameter." Or, as the "Steam Incas" website ([]) noted, these were one of the most successful New Zealand locomotive classes. An Ab could pull a 400-ton passenger train or a 750-ton freight over a relatively easy profile and has been described as the first locomotive in the world capable of developing 1 HP for every 100 lb (45.36 kg) of engine weight. (See Greenwood's careful reconstruction of the evidence supporting that claim.)

Jenkinson's 1922 analysis of the future of locomotives in New Zealand reported a record run in 1916 that produced an average horsepower of 637 (475 kW). He suggested that on that run the engine generated 1,000 hp (746 kW) at various points, burning coal at the rate of less than 2 lb per bhp-hour.

"It will be hardly credited," Jenkinson proclaimed,"that this power is developed from 1,500 sq ft of heating-surface, and 35 sq ft of grate area, and from a boiler weighing 15 tons, with all fittings, and that the prewar cost of the same was bout 900 pound, or 15 shillings per horse-power."

Noting that such figures would "stagger those conversant with boiler powes and costs generally", Jenkinson succintly laid out the case for steam locomotives, writing that the figure "represent fairly what can be expected from a well-designed modern locomotive-boiler with a superheater and large fire-box ....The fuel-efficiency of these boilers is extraordinarily high when working steadily at low blast-pressure."

Brian Greenwood, while agreeing in the main with the Ab's high reputation, reported that the first crosshead design's weakness had to be remedied by introducing a new cast crosshead. Bogie bearing troubles also were cured eventually by fitting roller bearings. The Vanderbilt tender design's draft gear wasn't satisfactory and the underframes were prone to rust.

The first of these engines didn't head to the scrapyard until 1956 Several left service in March 1969, the latest retirement dates for this subgroup.

NB: The direct heating surface (including the firebox heating surface) is an estimate calculated by subtracting the calculated tube heating surface from the reported total evaporative heating surface.

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Class Ab (Locobase 20282)

Data from Reference No. L759 or Code Word Aglistige builder's card in Locobase archive. See also S H Jenkinson, "The Future Development of the Locomotive in New Zealand", New Zealand Journal of Science and Technology, Volume 4, No 6 (January 1922), pp. 291-302. Works numbers did not track the road numbers, but in order of works numbers, NBLC delivered 22836-22860, 22866-22877 in 1921; 22879, 22881-22885 in 1922; 23039-23043 in 1923. (22878 and 22880 were lost in the SS WILTSHIRE when she wrecked on Great Barrier Island on 31 May 1922.

Locobase 2489 describes the Ab class's origins and performance. This entry shows the North British locomotives separately because of the significantly lower superheater area when compared to John Garner's figure for the class.

Withdrawals of the NBLC engines began in October 1958 with 775 (745 was written off after an accident in January 1957) and the last to leave service (823) was retired in July 1969.

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Class Ad (Locobase 5163)

Data from John Garner and his website [] (October 2002), supplemented by diagrams supplied by NZGR's general manager T Ronayne in "Locomotive Building in New Zealand", Railway Engineer, Volume 34, No 4 (April 1913), pp. 118-186.

These were unusual engines in many respects. First of all, they were de Glehn compounds, moreover, their low pressure cylinder diameters were smaller than their strokes. A limited loading gauge on the narrow-gauge may have required such a rare ratio. Even so, A L Beattie's design presented a compounding ratio just about centered in the usual range.

Second, the first four arrived with Stephenson gear inside, Walschaerts outside. The others had all Walschaerts gear. Interestingly, the Stephenson engines ran faster on the flat, but the all-Walschaerts locomotives were better in the hills.

Eventually the higher cost of maintaining compound locomotives led the NZR to rebuild all but one as two-cylinder simple-expansion engines between 1941 and 1949.

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Class G (rebuilds) (Locobase 5173)

Data from John Garner's comprehensive site at [] ... (October 2002). See also "New Zealand's Latest Locomotive - The "Gö Class", New Zealand Railways Magazine, Volume 12, Issue (1 November 1937), archived at [], last accessed 24 February 2019.

Outside valve gears were actuated by Walschaerts and the inside motion came from Gresley conjugated gear. Maximum cutoff was 50%.

Garner notes that these rebuilds of the overmuscled G-class Garratts were not particularly successful post-conversion either. Using the Ab's boiler with the three-cylinder running gear of the Garratt created an imbalance in which the cylinders emptied the boiler all too readily. In addition, the engines proved very slippery.. They were soon relegated to freight work, odd service for slippery Pacifics and indicative of just how unsatisfactory these engines had proved.

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Class Q (Locobase 2564)

Data from DeGolyer , Volume 24, p. 18. Some data from [] accessed in January 2002. 19202-19207 became 338-343, 19248-19254 were designated 344-350. Two arrived in December 1901, the majority in March 1902, and the last two in September 1902.

These were almost the first-ever "Pacifics." According to Hollingsworth (1982), it was NZGR's AW Beattie who responded to a Baldwin suggestion of a camelback 4-6-0 with the idea of putting a trailing axle under the bigger firebox. The larger grate was needed to burn the lower-calorie New Zealand lignite coal. The idea was accepted and the 4-6-2 came into being. They were numbered in order of their works numbers.

J J Parmalee of the NZGR wrote a progress report in a letter dated 3 April 1902. He noted that the engines had been modified at Dunedin, then sent to Qevercargill to enter service. He gave details of a series of spring and front truck adjustments as well as moving the equalizer fulcrum bolt forward 3" (76.2 mm). Parmalee added: "I did not recommend this [moving the fulcrum] as it does engines no good, but I did recommend leaves in back drivers and truck springs, and to move one ton from back drivers onto back truck which would equalize weights nicely [rest of sentence unclear]."

Then in a note any line manager will recognize, Parmalee concluded:" However, Government officials seem satisfied with their own way and engines are running well."

These engines ran successfully for many years, although one describes them as "not brilliant". . 340-341 and 344 went first in 1941. 1948 saw six retirements (338, 342, 345, 348-50). 347 was pulled in 1955 while 339, 343, and 346 lasted until 1957.