A.C. SPORTING CARS.
The Touring Models, Sports Models, and Racing Chassis.
THE A.C. Sporting car is naturally a direct descendant of the A.C. Touring car. The specification of the two are, as regards externals, identical.
The Sports chassis embodies certain modifications in design and materials so as to enable it to put up better performances on both road and track, but more especially, of course, on the former, as for track work the A.C. Racing model, which is a separate machine from the sports model, is more generally used. It is perhaps unnecessary, in these days of such wide knowledge of things that go to confer speed and power on a car, to specify the details of these modifications. Briefly enumerated they include alterations in the timing gear and perhaps also in the design of the camshaft so as to ensure the engine getting a full charge of mixture at high speeds, and reduction in the weight of some of the reciprocating parts. As regards the rest of the chassis, the difference between the sports and touring models is not great. A few opportunities are taken for weight reduction which may be made possible by the use of special materials for certain parts. Weight in the touring car chassis itself is already reduced so very nearly to the absolute minimum that these opportunities are very few and far between.
There are, of course, differences in the body work, and to this brief reference will be made in the course of what follows : the same remark applies to the racing car chassis.
A.C. One of the Original Light Cars.
Dealing then in the first case with the A.C. Touring car chassis, it may be worth while to commence by pointing out that the A.C. was amongst the earliest of light cars. It was developed as a real car, with all the essential details of such, at a time when the majority of cars of its capacity were of the cydecar type. Since those days its designers have kept in the forefront of their programme, one essential requirement, that of keeping the A.C. a real light car all the time, and they have never failed to realise that the true way of attaining economy of motoring, is by aid of scientific reduction of weight, to which end, however, no sacrifice either of comfort or quietness or any other desirable quality is tolerated.
Importance of Weight Reduction.
Looking at it from the motorist’s point of view, whether he may be a sporting or touring enthusiast, this matter is of outstanding importance. Every pound of unnecessary material in his car involves a constant drain from his pocket. Not only does it demand a greater consumption of fuel and tyres, but also implies increased wear and tear with a subsequent, and consequent, falling off n performance, as time goes on. When that expensive pound of weight is eliminated, the costs to which it inevitably gives rise are eliminated too.
To the sporting motorist this matter, however, makes a most pressing appeal, for he always has in mind the fact that by reducing the weight of the chassis, while maintaining the power of the engine at a maximum, his speed and performance factor is proportionally increased.
A ” Virtuous ” Circle.
Mr. S. P. Edge, in, drawing attention to this matter, has pointed out that the engineer who addresses himself to the problem of making a car lighter enters upon a “
virtuous” circle. For example, if he saves half an ounce in the piston the probabilities are that as a direct result of that economy he will save not less than Io pounds throughout the engine as a whole. A lighter engine in its turn will mean a lighter chassis so that in the end the economy of material will be considerable. Again, a lighter chassis means less load upon the engine, so that, apart from the sports necessity of improving the power-weight ratio, it is possible to follow the circle round again by diminishing the size of the engine, lightening its weight, and again lightening the chassis to suit, and so on.
There is, of course, a limit to the possible rational progress round this ” virtuous ” circle, otherwise there is a risk of emulating the coster who, by gradually reducing the daily allowance of food to his donkey, had at last got it almost to the point when it would be subsisting on nothing at all, when unfortunately it died. However, the fact certainly stands, that very considerable success has been met with by the designers of the A.C. car in this matter of weight reduction, as may be evidenced by consideration of the fact that the cheapest model A.C. is the ” Soveriegn,” and this complete and ready for the road, all on, as it were, weighs only 14 cwts.
The Four-Cylinder A.C.
The general design of the four-cylinder model with which which we are first dealing, embodies monobloccast cylinders, with separate air cooled exhaust manifold, and equipped with detachable head and end cover. The valves are totally enclosed and the camshaft, which
is lubricated by oil, fed under pressure, runs in three bearings. The tappets are fitted with rollers and have ample bearing surfaces to the guides. The tappet adjustment is carried out by screw and lock nuts.
Particular care is taken with the balance of the crank shaft, as also with that of all the reciprocating parts, so as to ensure freedom from vibration at nearly all speeds. The brackets for the starter and dynamo are somewhat ingeniously designed. Lubrication is by pressure through a crank pump, to all engine bearings through a drilled crank shaft, the piston and gudgeon pins being lubricated by splash in the usual manner.
Unusual Arrangement of Transmission Gears.
The arrangement of the transmission gear of A.C. cars is along unusual but not, of course, unique lines, in that the gear box is mounted in one with the rear axle casting. A fabric lined clutch transmits through a long propeller shaft to this gear box which is actually situated above the differential casing. The tube which surrounds the propeller shaft, the rear axle casing, and the gear box, are all of a special aluminium alloy which is claimed to be unusually strong, yet particularly light.
The brakes are arranged, one as a transmission brake, operated by hand, the other in drums and the rear wheels operated by foot. The location of the hand brake drum is unusual : it is in line with usual practice, in that it is behind the gear box. The main shaft of the gear box is prolonged and carries a disc which is mounted behind the rear axle. Actually, therefore, this drum, or disc as it really is, lies behind the rear axle.
The drums in the rear wheels are 12″ diameter and the brake gear, operated by the pedal, is designed for use as a service brake. The hand brake, however, will hold the car in any reasonable circumstances. Adjustment of the brakes is simple, that for the hand brake being by means of a nickel-plated nut which is accessible from the rear of the car. The foot-brakes are adjusted by other nuts which are easily accessible just in front of the rear wings at both sides of the car.
The Six-Cylinder Chassis.
As regards the six-cylinder chassis, this differs in its general design from the four-cylinder model in a.good many respects. The design of the engine is largely based on war-time experience of aero-engine construction, due regard, however, being had to the fact that an ordinary owner-driver of a car requires an engine which is as docile as it is lively, and capable of retaining its tune for long periods without attention. The six cylinders are set in a monobloc aluminium casting which is an open rectangular water jacket, making no direct contact with the cylinder wall except at their lower ends. The upper ends are spigoted into a combustion chamber formed in the detachable monobloc cylinder head. This system is a decided improvement in the usual practice, since the cooling water is in direct contact with the cylinder wails through their entire length. Moreover, on removal of the cylinder head, the water jacket can be cleaned as readily as the combustion chambers. The latter are dome-shaped and are machined and polished inside, thus reducing heat loss to a minimum and giving an exact equality of compression as between one cylinder and another. The overhead camshaft and rocker gear for the overhead valves are encased in the upper section of the cylinder head. The induction and exhaust passages are short and the valves are large and are so situated as to open directly into the spherical dome of the combustion chambers. A silent chain is used for the drive to the camshaft, and provision is made for automatic adjustment of its
tension. It is possible to remove the cylinder head without disturbing this chain.
Particular attention has been directed to the design of the aluminium manifold, so that practically equal distribution of the inlet gas is maintained. Furthermore, the inlet manifold is water-jacketed. Two exhaust pipes are provided leading to a large common silencer and the exhaust is correspondingly quiet.
The transmission on the six-cylinder model is through a patent disc clutch to a three-speed and reverse gear box with right-hand control. An enclosed propeller shaft is used and carries the drive to an overhead wormdriven rear axle. The brakes take effect, one on a disc at the end of the wormshaft, the other on the rear wheels. Quarter-elliptic springs are used for front and rear.
Gear Ratios of A.G. Cars.
The gear ratios of A.C. four-cylinder touring car chassis are top 4.5, second 8.2, first 16.2. In the sports model these are respectively 3.8, 7 and /4. In the six-cylinder chassis the top gear ratio is 4.33, the second 8.31 and the first 15.4. In the sports model the corresponding figures are 3.28, 6 and 12.
Amongst the main improvements which have been effected in A.C. cars for 1925 the following are worthy of special mention. Alteration has been made in the design of the cylinder water jackets and pipe, so that the effective cooling thus ensured, which is increased by the use of a slightly larger radiator, obviates the necessity for a cooling fan except in an abnormally hot climate. No cast iron is used anywhere throughout the chassis, except for the cylinder and combustion head. Every part taking a load or strain is made from steel forgings. The gear box has now more robust bearings and wider gears. The brake drums on the rear wheels are larger in diameter and the braking surface is now a combination of asbestos fabric and cast iron. ()Riess bushes are now fitted to the spring shackles and brake operating gear, leaving only three greasers on the whole car to have attention. Both axles are now provided with pads to receive the head of the
lifting jack, and stays are fitted between the rear axle casting and the tie rod to prevent accidental deformation of the axle when jacking up. The switchbox on the instrument board now incorporates the ignition switch and plug holes for an inspection lamp. A longer wheelbase has been provided for four-seater bodies and the driving position has been improved so as to afford a better view of the road.
The body design of the sports model has been considerably improved so as to reduce wind resistance. This will be apparent on comparing two of our illustrations, one of which shows the 1924 sports model with the comparatively short stubby tail and the other a 1925 one, which has a longer and more gradually tapering rear portion. A patent disappearing hood is now fitted, which when not in use lies entirely hidden beyond the rear seat. A sloping ” V ” type windscreen is fitted, the lower edge of which is shaped to follow the contour of the scuttle-dash, thus providing a perfect low line of vision. All the four springs on the sports model are bound with tape or whipcord. The body is finished in polished aluminium, and is equipped with disc wheels which are painted A.C. grey. The upholstery is in blue antique real leather and the usual equipment of tools and accessories is included.
The guaranteed chassis speed of the four-cylinder sports model on Brooklands Track is 70 m.p.h. over the flying half mile. If the purchaser is willing to pay the cost of the certificates issued by the Brooklands authorities, the speed will be demonstrated before delivery. The price of the four-cylinder sports fully equipped is 4500.
The six-cylinder sports model is guaranteed correspondingly to give 85 m.p.h. and its price is £630.
The Racing Model.
As regards the racing A.C. this, as has been stated, is special in a good many particulars. The combustion head of the engine is of bronze instead of cast iron, and the valves are carried in rocking guides which are the patent of Mr. Sydney Smith. Coil return springs are added to the rocking levers which now no longer
move across the stern of the guide as used to be the case.
A centrifugal water pump with intake at the centre through two pipes and delivering to the radiator through one is now fitted.
Everything that can be drilled to ensure lightness is so drilled, and some of the brackets and wheels seem to be, on examination, more holes than metal. Very free use is made of aluminium castings throughout the chassis, wherever its employment is at all practicable. The dimensions of the casting for the rear axle are reduced to a minimum, the shafts for the rear wheels projecting some distance on each side, instead of the casing being taken right up to the wheels as usually happens. The front axle has a torque tube which has a ball joint in the front of the crank case. The axle itself is tubular and its front steering tie rod is split to pass on either side of the starting handle-shaft.
Recent Performances of A.C. Cars.
It will be clearly remembered, by all readers of this journal, that an A.C. car ran well in the zoo miles race this year at Brooklands, being only beaten by the super-charged Darracqs. The latter, by their performances in that race, established several new records, including that for ioo miles, which had hitherto been held by the A.C. The opinion was expressed by many, at the time, that Mr. Edge would not long be content to allow that record to remain in other hands than his own, and it is interesting therefore, but not in the least surprising, to learn, just as we are going to press with this page, that J. A. Joyce, driving a 1,500 c.c. A.C. racing car, has again captured the zoo miles record, amongst many others of almost equal importance, if not so well sounding.
The hundred miles was covered in 57 mm. 35.30 sec., which is equal to 104.19 m.p.h., or 167.67 km.p.h. The hour record was broken at a speed of 104 miles 321 yards per hour, and the fastest lap, the 22nd, was covered at 105.52 m.p.h. One mile, one kilo, two miles, and five kilos, were all covered at 105.97 m.p.h. These and other records were established by a car the engine of which was not aided by a super-charger.