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


Class Details by Steve Llanso of Sweat House Media

Class K (Locobase 2485)

Data from John Garner, "Class K 4-8-4", on his New Zealand Railways Steam Locomotives website at [link], last accessed 2 December 2021. See also Brian Hollingsworth, The Great Book of Trains (London: Salamander Books, Ltd, 1987), pp. 130-131; H le Fleming (in Ransome-Wallis, 1959; Wikipedia's "NZR K Class"; and McCormack, Hayley. The Arrival of a MOTAT Icon. MOTAT Museum of Transport and Technology. First published: 15 May 2020. URL [link], last accessed 2 December 2021.

Large engines for this gauge and axle loading, these locomotive look much larger than they are until one takes in the size of the cab windows. They had 1 1/2"(38 mm) plate frames and 11" (279 mm) inside-admission piston valves. OS Nock (RWC V, pl 75) comments that "they were fast runners and topped 60 mph frequently." Tonnage ratings were 500-ton passenger trains at 50 mph (80 kph) or 1,000-ton freight trains at 30 mph (38 kph).

Like the later Ka batches (Locobase


Class Ka, Kb (Locobase 20966)

Data from John Garner, "Class Ka 4-8-4" on his New Zealand Railways Steam Locomotives website at [link], last accessed 2 December 2021. See also Brian Hollingsworth, The Great Book of Trains (London: Salamander Books, Ltd, 1987), pp. 130-131; H le Fleming (in Ransome-Wallis, 1959; Wikipedia's "NZR Ka Class" at [link]; and "NZR Kb Class"; and "Ka942" on the Mainline Steam website at [link], last accessed 14 December 2021 .

Several years after the introduction of 30 class K dual-service locomotives, NZR's Hutt works introduced the updated Ka engines. Extending the design, the new engines featured roller bearings on all axles and high-tensile-strength steel frames. Mainline Steam notes that the roller bearings eliminated the "bronze bushes that gave trouble on the thirty K class." Frame design changes extended the firebox cradle casting to just behind the rear driving axle, "reducing the amount of stress on the frame."

They retained the large grate and the 11" (279 mm) piston valves. H. le Fleming (in Ransome-Wallis, 1959) states that Ka engines actually picked up speed (from 23 to 26 mph/37-42 kph) on the 2% Raurimu spiral pulling 215 tons.

Kas 958-959 came fitted with Baker valve gear, which Wikipedia claims made them "quite free running on passenger train duties". On the other hand, these two were "less effective and powerful on freight trains compared to the rest of the class".

The steam excursion site [link] (10 October 2004) notes that as delivered, the Kas were "streamlined" with a casing that hid "the mass of pipework, two tanks and two pumps associated with the ACFI [Compagnie des Auxiliaires des Chemins de Fer et de l'Industrie] feed water appliance, mounted on top of the boiler, the smokebox, and on the running boards."

Never regarded as a handsome variation, the casing created eddies that pulled smoke and dust into the cab. When this apparatus was replaced by exhaust steam injectors in the late 1940s, the shops took off the casing.

All Kas operated on the North Island. Beginning in the later 1940s, all of the class was converted to oil burning and trailed tenders holding 1,900 US gallons (7,192 litres) of oil.

Taking the South Island's particular demands into account, the NZR's Hillside shops in Dunedin adopted the Ka design and put the first Kb in service in 1939, before Hutt put Kas on North Island service. A principal adaptation was the two-cylinder booster engine that added 8,000 lb (3,629 kg or 35.59 kN) to starting tractive effort as well assisting on the Midland Line between Springfield and Arthur's Pass. They also installed Nicholson thermic syphons in the firebox. High-quality West Coast coal proved quite acceptable and the Kbs were never converted to oil firing.

The inexorable inroads of diesel main-line power and railcars reduced both Ka and Kb numbers throughout the 1960s.

Ka 942 and Kb 968 evaded the ferro-knacker. Both ended up on the Mainline Steam roster.

Principal Dimensions by Steve Llanso of Middle Run Media
ClassKKa, Kb
Locobase ID2485 20966
RailroadNew Zealand Government RailwaysNew Zealand Government Railways
CountryNew ZealandNew Zealand
Whyte4-8-44-8-4
Number in Class3041
Road Numbers900-929930-964, 965-970
Gauge3'6"3'6"
Number Built3041
BuilderHuttHutt
Year19321939
Valve GearWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)14.25 / 4.3414.25 / 4.34
Engine Wheelbase (ft / m)34.83 / 10.6234.83 / 10.62
Ratio of driving wheelbase to overall engine wheelbase 0.41 0.41
Overall Wheelbase (engine & tender) (ft / m)58 / 17.6858 / 17.68
Axle Loading (Maximum Weight per Axle) (lbs / kg)30,968 / 14,04730,968 / 14,047
Weight on Drivers (lbs / kg)123,872 / 56,187123,872 / 56,187
Engine Weight (lbs / kg)194,208 / 88,091194,208 / 88,091
Tender Loaded Weight (lbs / kg)107,520 / 48,770107,520 / 48,770
Total Engine and Tender Weight (lbs / kg)301,728 / 136,861301,728 / 136,861
Tender Water Capacity (gals / ML)5950 / 22.545950 / 22.54
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)1900 / 7191.501900 / 7191.50
Minimum weight of rail (calculated) (lb/yd / kg/m)52 / 2652 / 26
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)54 / 137254 / 1372
Boiler Pressure (psi / kPa)204.50 / 1410204.50 / 1410
High Pressure Cylinders (dia x stroke) (in / mm)20" x 26" / 508x66020" x 26" / 508x660
Tractive Effort (lbs / kg)33,477 / 15184.9333,477 / 15184.93
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.70 3.70
Heating Ability
Tubes (number - dia) (in / mm)
Flues (number - dia) (in / mm)
Flue/Tube length (ft / m)17.60 / 5.3617.60 / 5.36
Firebox Area (sq ft / m2)190 / 17.65190 / 17.65
Grate Area (sq ft / m2)47.70 / 4.4347.70 / 4.43
Evaporative Heating Surface (sq ft / m2)1922 / 178.561922 / 178.56
Superheating Surface (sq ft / m2)428 / 36.42485 / 36.42
Combined Heating Surface (sq ft / m2)2350 / 214.982407 / 214.98
Evaporative Heating Surface/Cylinder Volume203.30203.30
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation97559755
Same as above plus superheater percentage11,51011,706
Same as above but substitute firebox area for grate area45,84946,626
Power L113,09014,089
Power MT931.881003.00

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