766 Series (G1)

A new type of front-coupled trailing bogie tank engine, specially fitted for working suburban traffic through the “Underground” to Moorgate Street, etc., was brought out at the close of 1889. Altogether, 25 engines were built of this class, together with four others of slightly different dimensions, and they were all provided with appliances for condensing steam in the tunnels, and were also built with shorter chimneys than usual, only 12-ft. 7-in. above the rail level, to meet the exigencies of the “Underground” loading gauge. The external appearance of the engines is shown in the accompanying illustration of No. 931, Fig. 81.

The leading dimensions of the 25 engines first built were as follows: cylinders 18-in. in diameter with a stroke of 26-in., angle of inclination towards the driving axle 1 in 8 3/4, driving wheels (four-coupled in front) 5-ft. 7 1/2-in. in diameter, and bogie wheels 3-ft. in diameter ; wheel-base : coupled axles, centre to centre, 7-ft. 3 -in., driving axle to leading bogie wheel axle, centre to centre, 10-ft. 3-in. ; bogie wheel-base 5-ft., with the bogie pin 3-in. in advance of the centre, thus giving a wheel-base from the leading wheel centre to the centre of bogie pin of 19-ft. 9-in. ; total wheel-base 22-ft. 6-in. Total length of frame plates 29-ft. 3-in., the overhang being 5-ft. 3-in. at the leading end and 4-ft. 3-in. at the trailing end, measured from the bogie pin ; height of top of outer frame plates 4-ft. 2-in. The boiler barrel was 10-ft. 1-in. in length, with a diameter outside the smallest ring of 4-ft. o^-in., and it was pitched with its centre line 7-ft. 3-in. above the rail level ; length of firebox casing 5-ft. 6-in. Heating surface and grate area were practically identical with those of the latest standard goods engines already described. Capacity of side tanks 1,000 gallons. Empty, engines of this class weighed 45 tons 4 cwt., while in full working order the total was 53 tons 9 cwt., distributed as follows: leading wheels 17 tons 7 cwt. 2 qrs., driving wheels 17 tons 16 cwt., and bogie wheels 18 tons 5 cwt. 2 qrs. These engines were built at Doncaster and numbered in the order given below :—

A modified pattern of the latest standard type of bogie tank engine, fitted for working through the “Underground,” was brought out in 1895. Four engines were built to this new design in the following order : —

In external appearance, as can be seen from the accompanying illustration. Fig. 86, these engines were very similar to their predecessors, the chief difference being that the side tanks were shorter. The supply of water was, in fact divided over the two side tanks and a well tank placed at the rear of the foot-plate, below the coal bunker. In general dimensions these latter engines were almost identical width their forerunners, as will be gathered from the accompanying list. Diameter of driving wheels 5-ft. 7 1/2 in., and of bogie wheels 3-ft. Wheel-base: coupled wheels 7-ft. 3-in., from centre of driving axle to centre of leading bogie axle lo-ft. g-in., centre to centre of bogie wheels 5 ft., total wheel-base 23-ft. Cylinders 8 in. by 26 in., inclined downwards, as usual, in the ratio of 1 in 8 3/4. Boiler barrel lo-ft. i-in. long, with a diameter outside the smallest ring of 4-ft. o 1/2 in. ; height of centre above rails 7-ft. 3-in. ; and of chimney top above rails 12-ft. 7 in. Firebox casing 5 ft. 6 in. long outside, with a depth below the centre line of the boiler of 5-ft. 2-in. and 4-ft. 8-in., at front and back ends respectively. The weight was approximately the same as in the earlier engines, but rather; differently distributed.