The next class to make its appearance was a marked development of Mr. Stirling’s early design of locomotive for working the underground suburban traffic to Moorgate Street and the South of London. While retaining the four 5-ft. 7-in. driving wheels, coupled in front, this new class of engine had the trailing end carried on a four-wheeled bogie, thus constituting a much easier riding engine. At the same time the gross weight of the locomotive in full working order was actually less than that of the earlier six-wheeled type.
The leading dimensions of these locomotives were as follows : cylinders 17 1/2-in. in diameter with a stroke of 24-in. ; diameter of driving wheels 5-ft. 7-in., and of bogie wheels 3-ft. i-in. ; wheel-base: coupled wheels 7-ft. 3-in., driving wheels to leading bogie wheels lo-ft. 3-in., leading bogie wheels to centre of bogie pin 2-ft. 3-in., bogie pin to trailing bogie wheels 2-ft. g-in., total wheel-base 22-ft. 6-in. ; over-hang of frame plates at leading end 5-ft. 3-in., and at trailing end 4-ft. 3-in. from bogie pin, total length of frame plates, 27-ft. The boiler was pitched with its centre 7-ft. above the rail level, having a length of barrel of 9-ft. 10-in., and a diameter inside the smallest ring of 3-ft. 9 1/2-in., and
the firebox casing measured 4-ft. 6-in. in length, with a depth below the centre line of the boiler of 5-ft. 1-in. at the leading end, and 4-ft. 7-in. at the back. The heating surface was: tubes 806 sq. ft., firebox 81 sq. ft., thus giving a total of 887 sq. ft.
Over the bogie was a large tank and bunker having a capacity for 1000 gallons of water and 30 cwt. of coal. The total weight in working order was 40 tons 14 cwt. 3 qrs., distributed as follows:— leading wheels 11 tons 10 cwt. 3 qrs., driving wheels 14 tons 14 cwt., and bogie wheels, 14 tons 10 cwt.
In all, 48 engines of this type were built at Doncaster between the years 1872 and 1881, their dates, works numbers and running numbers being as follows:—
|Date.||Doncaster No.||Engine No.||Date||Doncaster No.||Engine No.|
Of the list given above, however, more than one-half, from No. 621 onwards, were provided with larger tanks and bunkers at the trailing end, which also caused a corresponding increase of the total weight of the engines. The accompanying illustrations of Nos. 517 and 246, Figs. 46 and 47 respectively, show the leading external characteristics of these two classes of engine. It will be noticed that the earlier class had the number plates on the side sheets, while the later ones had them on the sides of the bunkers. Some of the earlier engines, however, among which were Nos. 241, 245, 248, 507, 513, 515 and 516, were afterwards fitted with larger bunkers, and then had the number plates removed to the position shown in Fig. 47. These engines, and those of the 126 class, together with rebuilds of Mr. Sturrock’s Metropolitan engines, are the only types on the G.N.R. with brass number plates. Nos. 510, 511, 513, 515, 528, 529, 531, 241 to 250, 621 to 628, 654 and 655 were fitted with condensing apparatus for working through the “underground,” and were also provided with shorter chimneys, so as to pass the Metropolitan Railway loading gauge. The two engines, Nos. 629 and 630, which are included in the foregoing list, should really be considered as a separate type.