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Armstrong Siddeley 15hp

As the mid 1920s progressed and the side valve, six-cylinder engine 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 as 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. The conversation might turn to the engineering highlights, features such as the crankshaft and camshaft now each supported by four bearings, the aluminium covers to the timing chain and sump, the water pump and electric starter along with the other ancillaries, were all items to cheer the heart.

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Armstrong Siddeley long 15hp 1933 3.jpg
Armstrong Siddeley long 15hp 1931 1.jpg

From a practical standpoint, the detachable head made 'decoking' at 10,000 mile intervals so much easier and less time consuming. 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 cars. 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, only now the engine fulfilled the public's aspirations.

As an aside, it is interesting to note that it would be another 28 years before an Armstrong Siddeley car again sported a four cylinder engine.

The new 15hp. car would, however, over the next three years, undergo five major changes which would reflect in the development of all models of Armstrong Siddeley cars into the 1930s


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.

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Armstrong Siddeley 1931 15hp Mulliner.jpg
Armstrong Siddeley long 15hp 1933 9.jpg

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 now 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.

Armstrong Siddeley long 15hp 1933 20.jpg

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 stable mates.


Steps were taken to allow the now lengthened chassis of the 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 preselective ball joint fixing and torque tube assembly.  Semi-elliptic springs continued to be fitted all round, under slung 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 was now fitted.

The New Long 15hp was announced in time for the 1930  'London Motor Show and Paris Salon'

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Alterations and improvements continued to be made. In 1931 attention was directed to reducing the noise and inherent vibrations of a piston engine by applying a damping mechanism to the free end of the crankshaft - commonly known as a vibration damper.


The following year saw a number of changes. The first applied to all the cars in the then current range which of course included the 15hp. This was the departure from the flywheel fan with side trays for engine cooling to a belt driven front of engine mounted fan acting directly on the radiator which would become the industry standard for many years to come.


At the opposite end of the car a change to a lift-off petrol filler-cap was made. Secured by a spring it could be hooked to the top lip of the filler pipe which ensured that it was not left at the pump after filling with fuel. Perhaps one is less sure about the claim that it prevented the cap from being stolen.


November 1932 saw the six cylinder side valve engine have the piston stroke lengthened from 101.6mm to 114mm increasing capacity from 1928cc to 2169cc which along with induction improvements gave a power boost to the car. To counter this the brakes were upgraded to the Bendix 'servo' four wheel cable operated system which gave a stopping distance of 67 feet when applied at 30mph and 100 feet at 50 mph.


The battery was moved to under the rear seats and now took the form of two 6 volt batteries placed each side of the prop-shaft tube and coupled together to give the 12 volts required.

During 1933 the Claudel Hobson down draught carburettor became the standard fitting for these cars.


The 15hp continued into 1934 when it was replaced by the new 17hp car.

Today in an era of mass production it seems unbelievable to us that with so many changes, alterations and improvements it was possible to make good profits from the car division of the company. However we must remember the realisation of mechanical transport for the individual was just coming out of its infancy.


Perhaps we are seeing a similar trend in this generation as manufacturers of electric cars endeavour to hone the product into one which will satisfy the buying public, giving style, comfort, performance and the all important range between charging.

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Armstrong Siddeley 1931 15hp Mulliner 3.jpg
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