In the mid 1930's the oil pipeline network in the Arabian States was still in its infancy. The only option for moving oil from refineries to the depots not served by pipeline was the lorry.
Scammell Lorries Ltd built two articulated tankers to the specification required by the Anglo Iranian Oil Company for this work in 1935. A high road speed and the ability to climb long hills with varying gradients and hairpin bends to an altitude of 10,000 feet was needed in addition to good cross-country ability. This had to be achieved with a payload of 4,000 gallons weighing 14.5 tons.
To provide the power necessary to cope with the arduous conditions, Scammell used a Parsons straight-eight marine engine. This was converted from marine to road use by Scammell at their Watford works.
The heavy cast iron crankcase was replaced with aluminium with the 8 cylinders cast in pairs. New cylinder heads of Scammell design replaced the originals. The cylinders were arranged in two groups of four, each with its own exhaust and inlet manifolds. The cast pistons were replaced with aluminium ones in the unlined bores and a centrifugal type governor was fitted. The result was a 14 litre petrol engine with 4.8:1 compression ration giving 160bhp.
Two Claudel Hobson down-draught carburettors were fed by two Amal 170 pints per hour fuel pumps from two 45 gallon chassis mounted fuel tanks. Ignition was by magneto and coil with separate distributors and plugs for each system. The coil ignition was used for starting and the magneto for normal running. Cooling was by an extra large still-tube type radiator incorporating the 'Coffee Pot' header tank as used on the Pioneer.
The transmission was a strengthened Pioneer five-speed gearbox. This was coupled to a double-layshaft auxiliary box of Scammell design. Strengthened rocking beam axles from the Pioneer provided the drive in 6x4 configuration.
The front beam axle was mounted on semi-elliptic steel leaf springs. These were shackled to the chassis and to a floating cross beam. The cross beam was mounted to the front of the chassis using Gruss air suspension units made by J MacDonald and Co (pneumatic Tools) of Glasgow. The resultant articulation of the front axle, coupled to the rocking beam rear bogie provided the necessary cross-country versatility. Tyres were Dunlop 13.50x20 on both prime mover and trailer.
The braking system was a Clayton Dewandre compressed air type with a twin cylinder water cooled compressor driven from the engine. A mechanical brake was fitted to the drive axles and a Neate brake fitted to the trailer, which also had a cable operated parking brake.
The trailer was coupled to the unit by way of a steel ball in a phosphor bronze cup mounted under the trailer. This cup located into the king-pin socket which was mounted on two leaf springs fixed transversely to the chassis directly above the drive axles.
The chassisless trailer consisted of a tank built by Thompson Brothers of Bilston mounted onto a Scammell designed two axle bogie. The bogie used two inverted semi-elliptical steel leaf springs, centrally mounted to the frame and with radius arms shackled to their ends. This allowed independent movement of each individual wheel.
The tank contained three compartments. The two rearmost were of 2,000 gallon capacity each with a 200 gallon compartment in the front. This small tank was the reserve tank for the prime mover.
The cabin had provision for a man to sleep in the passenger side and contained a tank for fresh drinking water. A fireproof screen behind the cab and upturned exhausts were fitted to comply with petrol regulations.
The completed vehicle weighed 13.5 tons giving a gross weight of 28 tons when fully loaded and was capable of maintaining 35 m.p.h. on the open road. Although able to cope admirably with the conditions, the Scammells were heavy and expensive, resulting in only two being built.
From my article in Vintage Roadscene, Vol 5-17, December 1988-February 1989.