NEW ZEALAND RAILWAY STEAM 5




The ten “Aa” class Pacific type locomotives supplied by Baldwin in 1914 were classical American in every way. I never knew them in their original form but caught up with them towards the end of WW2 by which time they had been rebuilt with “Ab” boilers and cabs and redesigned tenders. They were also equipped with compressed air power reversing. They hauled freight mainly between Palmerston North and Taihape, were good steamers but not as freely as the “Abs”, and rough riders at speed over 35 MPH. An oddity was that the shafts of the fire shovels of both the originals and rebuilds were three inches longer than those belonging to all of the other NZR locomotive classes.

Palmerston North was home-base for a fleet of “Bb” class 4-8-0 tender engines that performed the yard shunting, ran the usually lightly loaded Foxton branch goods daily service and supplied exchange locomotives for Marton Junction and Danevirke. Originally built for main line freight work they were grossly under boilered or over cylindered with their small narrow fireboxes, but proved highly successful in the main shunting yards up to the end of steam.

There was nowhere on the NZR network that members of the 141 “Abs” did not run. They represented the definitive locomotive of the time. They handled all of the main passenger trains relatively efficiently and economically. Indeed, they were incredibly free steamers and of most uncomplicated configuration. Their weight distribution was a little short of ideal being light on the leading bogie and heavy on the rear end single axle truck. Through their lives two tons of cast iron weight was added to the front ends. They were prone to fracturing their main frames through the arches behind the cylinders. Indeed one that I was on with a provincial express clean broke on one side at speed a mile short of our crew change point. The thumping with each piston stroke was like that of a power hammer.

The “Wab” engines were the tank version of the ubiquitous “Abs”. They had the same boiler, cylinders, running gear and cab. The rear bogie was of the two axle trailing type to carry the added weight of the coal bunker. The side mounted water tanks provided useful weight over the driving wheels that enabled the boiler pressure to be raised to 200 PSI thus returning an additional 2366 pounds pull at the drawbar. Although there was higher demand on the boilers they steamed even more freely than the “Abs” from which they were derived. They rode well but forward vision was restricted by the height of the tanks and their projection of 3 inches outside the width of the cabs. In the latter days of steam several of them were converted to “Ab” class tender locomotives.

The new “Ka” engines coming on line were a quantum leap in quality of service with their massive roller bearing axle boxes and extremely free steaming boilers. They rode well and the running gear gave trouble free service between programmed overhauls. They bore a clumsy style of so called stream-line smoke-box and boiler-top casings that added nothing to the aesthetics and hampered the maintenance staff. They were also equipped with the French ACFI feed-water heating system with which I was familiar on the Taihape based “K” 919. About halfway through completion of the “Ka” order the fitting of the cowlings and ACFI system was discontinued and eventually removed from all engines of the class. Easily maintained exhaust steam injectors as on the original “Ks” were made standard equipment.

The 40 “J” class engines of my time followed by 51 closely related “Jas” and “Jbs” to make a total of 91 with their oil sealed Cannon roller bearing driving axle assemblies and Baker valve gear were probably the NZR’s finest steam locomotive package. The first 40 bore fairings along the tops of the boilers that hid the funnels and steam and sand domes. The smoke-boxes bore coned fronts with the headlamps in the centres. This paraphernalia was eventually removed and all members of the class were turned out in their naked glory.