The next new class of engine constructed at Doncaster was a large eight-coupled tank locomotive with a pair of trailing wheels. This engine, No. 116, which is illustrated in Fig. 109, was, as originally built, so far as boiler. cylinders and wheels were concerned, practically identical in dimensions with the eight-coupled mineral engines of the “401 ” class, with the addition of side tanks and an end bunker, and condensing apparatus, this last being fitted with the intention that this locomotive should work passenger and goods traffic over the Metropolitan ” underground ” section of the G.N.R., and the chimney and steam dome were of a modified pattern in order to pass the Metropolitan loading gauge.
The cylinders were 19 3/4-in. in diameter, with a stroke of 26-in. The diameter of the eight-coupled wheels was 4-ft. 7 1/2-in., and of the radial trailing wheels 3-ft. 7 1/2-in.
The total wheel-base was 25-ft. 2-in., the two middle pairs of coupled wheels being 5-ft. 8-in. apart, centre to centre, and the two extreme pairs being respectively distant from these to the extent of 6-ft., whilst the trailing axle was 7-ft. 6-in. to the rear of the last coupled axle, centre to centre. The engine measured 35-ft. 7 1/4-in. over the buffer beams, the overhang being 6-ft. 5-in. and 4-ft. 0 1/4-in. at leading and trailing ends respectively ; the total length over all was 38-ft. 7 1/4-in. The boiler originally supplied was similar to that of the No. 401 class, and its centre line was 8-ft. 4-in. above the rails. As originally built, the side tanks and bunker were of exceptionally large capacity, being built to hold 2,000 gallons of water and 4 tons of coal respectively. In road-worthy condition, the engine weighed a total of 79 tons, the distribution being : on leading coupled wheels, 15 tons; on driving, intermediate and trailing coupled wheels, 17 tons per axle ; and on trailing radial wheels, 13 tons.
Almost immediately after being put in service, this powerful and otherwise successful engine was found to be too heavy for the Metropolitan line, and in response to the requirements of the permanent way department, Mr. Ivatt undertook so to modify the design as materially to reduce the gross moving load. With this end in view, he removed the boiler originally provided, and replaced it by one having a length of barrel of 11 -ft. 9-in., and a minimum diameter, inside, of 3-ft. 11 3/4-in.; the firebox was also reduced to 6-ft. 2-in. in length. This new boiler had a total heating surface of 1,043.7 sq. ft., of which the firebox contributed 107.7 sq. ft., and the tubes 936 sq. ft. ; the grate area was 17.8 sq. ft.
At the same time, the side tanks were reduced in length, lessening their capacity to 1,500 gallons, and only 3 tons of coal were carried. As thus modified, the engine weighed 70 tons 5 cwt., distributed as follows: on leading wheels 13 tons 10 cwt., on driving wheels 15 tons 5 cwt,, on intermediate coupled wheels 15 tons, on trailing coupled wheels 14 tons 10 cwt., and on trailing radial wheels 12 tons.
No. 116 ran for some time in its modified form, as shown in Fig. no, before being followed by others of the same class, but eventually a series, built in accordance with the revised dimensions, were built at Doncaster in the following order : —
|Date.||Doncaster No.||Engine No.||Date.||Doncaster No.||Engine No.|
Nos. 127-136, which had 19 3/4-in. cylinders, on completion, instead of being sent to the Metropolitan district, were stationed at Colwick, to work coal trains over the Nottinghamshire branch lines, and these were followed to the same depot by Nos. 137- 141, which began work between Colwick sidings and Pinxton, and later by Nos. 142-151, all these having 18-in. cylinders. At the beginning of 1908,
Nos. 1 16-126 were removed from London to Colwick, and prior to getting to work there had their cylinders reduced from 19 3/4-in. to 18-in. diameter, and tlie condensing gear removed. Nos. 1 27-131 were similarly stripped of their condensing gear and sent to Ardsley (Leeds). Nos. 127-136 are the only engines of the class now running with 19 3/4-in. cylinders. In October, 1909, No. 133 of this class was rebuilt with a boiler similar to that originally fitted to No. 116, bringing the total weight, with tanks full and 2 1/2 tons of coal in the bunker, up to 71 tons 7 cwt.