The construction followed in principle a design first adopted by Wickham in 1936 for use on a South American mountain railway, where weight saving was of vital importance. Vehicles were still in service by 1957 and the bodies had given no trouble at all. Similar sets were also working by that time in Bolivia, Peru, Columbia, Venezuela, Tasmania and in East & West Africa. No underframe was used, the all steel body skeleton formed a tubular stress bearing box girder designed to take all bending, torsional, buffing and traction loads. The various items of equipment were attached by means of steel brackets welded on as necessary.

The girder was formed from solid drawn square steel tubing with a wall thickness of approximately 1/8 in (10 gauge) and as each was, during assembly and welding, completely closed to atmosphere, no internal corrosion could occur. The skeleton of the power car weighed only 5 ¼ tons. The 16 gauge corrugated steel flooring was welded to the tubular longitudinal and cross frame members giving additional strength for taking care of buffing loads. The roof sticks on the cars were most unusual, and was due to the fact that most of the Wickham railcars previously built were shipped abroad to numerous different countries with different width and contour requirements, and so it was not practical to make press tools for every different type. The Class 109s had two flat members spaced apart by a zigzag strip and welded as a unit, which required only simple fixtures for manufacturing and was light and rigid. A load of 1 ½ tons spread over the centre six inches produced a deflection of only 5/16 in. A further advantage was the ease with which the wiring conduit, supply and control services could be run through the gaps.

This rigid stress bearing structure allowed the body frame to be initially fabricated in fully rotating fixtures by electric welding. Similar fixtures were used in the erection shop for easy fitting of wiring, pipework, engines and transmission, the cars being revolved to the most suitable position for the work in hand.

A vehicle in the rotary manipulator. Through the second mans window can be seen a man working with ease on the ceiling sections half way along.

Aluminium sheets were supplied by British Aluminium Ltd, who also supplied the aluminium tubes and sections along with Northern Aluminium Ltd. Asbestos insulation came from Sprayed Insulations Ltd. The square section steel came from Accles & Pollock Ltd. Fire protection equipment came from Graviner Manufacturing Co Ltd. The whole of the door locks were supplied by Joseph Kaye & Sons Ltd of Leeds. Both Docker Brothers Ltd and Vulcan Products Ltd supplied the paints and varnish.

Unusually, aluminium was used for the fuel and vacuum tanks, which were electrically welded by the argon arc process, and solid drawn aluminium tubing was used for the vacuum brake pipe layout. Compressed air control piping was of solid drawn steel tube, thought to eliminate to a large degree troubles caused by scale loosening and choking control valves. Ermeto couplings were used for connections.

Load Testing

This comprised strong-backs distributed over the railcar floor area, spring loaded bolts being passed through this floor and attached to eyebolts grouted in concrete. Load was applied by hand wheels on each strong-back through calibrated springs, the body skeleton being supported at the bogie centres.

Integral body frame under load testing. Note the spring-loaded bolts along the vehicle floor are attached to the floor of the workshop.

Bogies

The standard Derby design bogies were used, with a wheelbase of 8' 6", modified in certain details by welded assemblies in place of riveted construction and the fitting of Woodhead-Monroe hydraulic shock absorbers between bolster and body. Lighter springing was made possible by the weight saving method of construction. Trial runs showed the riding and general performance to be very satisfactory. Rubber mouldings were supplied by Waterford Rubber Manufacturing Co, and springs from Turton Bros & Matthews Ltd and Jonas Woodhead & Sons Ltd.

The top design speed of the unit was the standard 65mph at maximum governed engine speed of 1,800rpm, although as the tare weight of the car and trailer was only just 47tons the manufacturers confidently expected better acceleration and lower fuel consumption.

Brakes were the standard Gresham & Craven Ltd quick release system. Buffers were supplied by Oleo Pneumatics Ltd. British Timken Ltd supplied the axleboxes, with John Baker & Bessemer Ltd supplying the wheels and axles. Speed indicator equipment came from J Stone & Co Ltd. Steel castings came from Lake & Elliot Ltd. Screw couplings came from W&E Moore Ltd, and compression joints from the British Ermeto Corp Ltd. Aluminium pipe fittings were supplied by William E. Cotton Ltd, and the heaters by S Smith & Son Ltd.

The engines, transmission, control gear and heating followed the British Railways standard design and was supplied by British United Transport. They used the 'L' type 150hp engines with fluid couplings each driving via a cardan shaft an air operated four speed Wilson epicyclic gearbox, the drive from each gearbox to its adjacent bogie was by Hardy Spicer propeller shaft to a BUT double-bevel reverse box mounted on the inner axle. The various auxiliary drives to fan, Stone dynamo and Clayton exhauster also followed the standard pattern.

The rotary manipulator allowed this view of a DMBS underframe before the engines were fitted.

Cab

Standard BUT 'L' type cab controls were used, with the tachometers, vacuum & pressure gauges mounted on a sloping panel between the throttle and gear controllers. This panel also carried the main switch, main switch indicator light and changeover switch for the revolution counter. Indicator lamps were mounted on a vertical panel, on the left and at an angle to the driver so that they can be observed without craning the neck, being at the same time clear of the driver's ahead vision. On the right within comfortable reach of the drivers hand was the Gresham & Craven vacuum brake valve. The hand brake wheel was also within the drivers reach without leaving his seat. A comfortably upholstered Chapman driving seat was fitted, which was fully adjustable for height and could be moved forwards or backwards by the driver as required.

The drivers controls. Note the sloping panel in front of the driver containing the gauges.

Interior

Both the exterior and interior panelling was of 16 gauge aluminium sheet, the inside panelling up to luggage rack level had Warerite plastic veneer sheeting bonded to the surface. The roof covering over the luggage racks was corrugated rubber, roof panels were Vynide cloth covered. Both the first and second class saloons had the Warerite interior finish, first class in simulated walnut and the second class light oak. Very few panel fixing screws were visible, all others were covered at the top by the tubular aluminium luggage racks and at the bottom by the heater duct, special extruded aluminium sections with suitable locating grooves and special section window frames provided neat and rattle proof retaining fixings. Bakelite supplied the Warerite panels for the interior. The leathercloth was supplied by ICI Ltd.

Heating ducts and the roof vents were supplied by Aircraft Materials Ltd, and luggage rack brackets came from Dean & Sons Ltd. Hinges came from Beaton & Sons.

The Widney windows, apart from the special frames were of the standard British Railways design with polished and aluminium finish. These windows had the standard sliding top lights with deflectors at the top for ventilation purposes, further ventilation was supplied by Airvac roof ventilators, the roof openings being concealed by the longitudinal troughing which also supported the interior lights. The windows were supplied by Hallam Sleigh & Chester Ltd and Beckett, Laycock & Watkinson Ltd.

Draught deflection partitions were arranged at each entrance door, these were fitted with glass panels and shaped to give a light and spacious appearance.

The corrugated steel floor was filled with sprayed asbestos for sound insulation and then covered with asbestos filled flame-proof hardboard, the final floor covering being of heat resistant rubber sheeting. The flooring material came from Rubberware Ltd, and the flooring sections from Metal Sections Ltd. In the power car suitable traps fitted with locks were fitted over vital parts of engine and transmission but all normal servicing could be carried out from the side or over pits.

Steel tubular framed seats were supplied by GD Peters of Slough and arranged 2 + 3 in 2nd class, with a patterned green moquette with leather trim on Dunlopillo. The 1st class saloon, arranged 2+2 were of a similar design, but gave a suitably greater degree of comfort, and finished in blue moquette with leather trim.

2nd class saloon

The guard's compartment was laid out to meet British Railways standards. A seat, electric food warmer, first aid kit and accident equipment including ladders were provided.

Only the trailer car had a toilet, this being accessible from the power car through the standard bellows gangway supplied by AG Wild & Co Ltd. The partitions into the driving cab had lockable sliding doors.