Armstrong Siddeley 15hp
This Page is under development
As the mid 1920s progressed and the side valve, six cylinder engines gained favour with the buying public the company set in motion plans to develop the 14/4 into what would become the 15HP car.
Introduced to the market in 1927 the car was very much the 14/4 but with the major change being under the bonnet. The new owner could now lift the bonnet side panel and proudly display the six cylinder, 1900cc monoblock engine housing a four bearing crankshaft and four bearing camshaft,
The cast iron crankcase concealed the parallel valves, the timing chain cover of aluminium, as was the sump. Under the trays which were a close fit to the engine to ensure a good draw of air through the radiator produced by the flywheel mounted cooling fan.
The detachable head, making 'decoking' at 10,000 mile intervals so much easier, along with the water pump and electric starter were all items to cheer the heart. The day of the owner driver was by 1930 well established. The larger tasks were still left to the local dealer/garage to perform, but a majority of drivers understood the basics and truly cared for their car. After all it was probably the second most expensive life purchase they would make. The dimensions of the chassis, wheelbase and layout remained the same as the 14/4, only now the engine fulfilled the public's aspirations.
The new 15hp. car would however, over the next three years, undergo five major changes which would reflect in the progress of Armstrong Siddeley cars into the 1930s. As an aside, it is interesting that it would be another 28 years before an Armstrong Siddeley car again sported a four cylinder engine.
In the April of 1928, after 1150, 15hp. cars had been produced, a new chassis layout was introduced with the rear springs now mounted under the rear axle, which required the springs to be lengthened, also the axle ratio was increased from 5.1 to 1 to 5.5 to 1. The merit of this change would seem to be that the centre of gravity was lowered which gave greater stability, especially in cornering, as roads improved and vehicle cruising speeds increased. It also facilitated stepping in and out of the vehicle and made for a 'sportier' look.
In February 1929 when 2500 cars had been constructed the 15hp was designated the 15hp. Mk2. No dramatic changes were made but over the next 200 cars constructed incremental changes continued to be made. The water pump was no longer driven by a common shaft with the dynamo, but was now placed in the centre of the timing cover and driven off the camshaft. Then a new type of steering was introduced followed by an improved radiator. Gear ratios were changed and the handbrake improved.
In July 1929, now almost 4000 cars down the line, the scuttle mounted fuel tank (10 gallons capacity) was moved to the rear of the chassis and some 250 cars later in December, enlarged to 12 gallons. This change replaced the gravity fed feed to the Claudel Hobson carburettor and necessitated the introduction of an engine mounted fuel pump. The luggage grid fixed to the rear of the car was modified and the spare wheel mounted on the running board, while the battery was brought 'indoors' and placed under the driver's seat. The radiator cowl was chromed but only the beading to the front and rear edges showed as the space between was painted in the body colour. A feature on Armstrong Siddeley cars of the thirties which distinguished them from most of their competitors. Some A.S. cars when restored have had the radiator cowl given the full chrome treatment, but this is the owner’s choice to which he or she is fully entitled.
Having moved the scuttle mounted fuel tank changes were made to the dashboard, A double dashboard was experimented with to allow for the storage of tools. The Instrument layout was changed and included a petrol gauge and ammeter. Ancillaries, such as side and headlamps, window surrounds etc, were all now chrome plated. The final changes made in March 1930 were the introduction of the Wilson 4 speed preselective gearbox, a banjo type rear axle and the moving of the handbrake lever to the driver's side of the car,
By now the 15hp car had changed greatly from the 14/4 car from which it stemmed. Indeed one might be forgiven for concluding that the 15hp Mk 2 cars were used as a test bed for proving ideas and developments which would, if satisfactory, be introduced to the complete range of cars as the new decade of the thirties approached
Once again at the beginning of October 1930 changes continued to be made to the specification of the car.
The most obvious being the fitting of the traditional Armstrong Siddeley ‘V’ shaped radiator to bring the car in line with its larger stablemates.
Steps were taken to allow the now lengthened chassis of the 15hp.car to be even closer to the ground with a deep and wide cross member introduced to brace the frame while providing a mounting point for the pre-selective ball joint fixing and torque tube assembly. Semi-elliptic springs continued to be fitted all round, underslung at the rear, but now with 'Silent bloc' type bushes in the eyes of the springs. (The Silent bloc Company was not formed till 1935) Engine power was improved by modifying the combustion chambers and repositioning the spark plugs.
Engine cooling water flow was improved and the latest pump type V36 BD Claudel Hobson Carburettor now fitted.
The New Long 15hp was announced in time for the 1930 ‘London Motor Show and Paris Salon' held at Olympia.
In an earlier paragraph we mentioned the need for the engine to be 'decoked' as part of the servicing at 10.000 mile intervals. It was normal to lap in the valves as part of this activity in order to ensure a good seal. To many readers, familiar only with modern cars, this may be a somewhat puzzling requirement. Fuel at this time was unleaded and contained no additives. This caused a considerable build up of carbon in the combustion chambers resulting in a falling away in performance. It was only after 1930 that fuel containing the lead and 'anti- knock' additives with which we are familiar began to be used.
Having completed this procedure replacing the head gasket and tightening down the head require care that it be put down evenly to ensure a good seal and avoid straining the fixing studs. It must be remembered back than torque wrenches and lb/ft settings were unheard of. The approved way to tighten a nut was to turn it until the open ended spanner just started to slip off the nut. If you ever wondered why spanners are of differing lengths, it is because they were designed to prevent over tightening of the appropriate sized nuts and consequent stripping of the thread.
Long 15hp car.
wheelbase -9ft 7 in long and 4ft 8in wide.
Overall length 13ft 1in. width 5ft 8in.
Next section the 1930 to 1934 15hp. cars ?