THE 12-CYLINDER

THE 12-CYLINDER ROLLS-ROYCE

Once again the unhurried policy and the unrivalled technical resources of Messrs. Rolls-Royce have permitted them to produce a masterpiece amongst motorcars. 12-cylinder aero engines have been built at Derby for the last twenty years, and an experimental 12-cylinder car was tested on the road shortly after the war. This model was considered too advanced to be put on the market at that time, and so the 6-cylinder with successive improvements continued to be the favoured type. The 12-cylinder car was however by no means forgotten, and now when the time is ripe the Phantom III makes its bow, embodying all the modern developments which have been tried and found of value since the debut of the Phantom

In order to attain easy and luxurious travel with luxurious coachwork it is essential to have a large engine, and under these conditions a 12-cylinder unit oilers important advantages. Light reciprocating parts can be used, the torque and acceleration are improved and more silent running results. Th6 engine speed and with it the power output may be raised withOut increasing the stresses on the working parts and, even with a slight reduction in capacity, the 12-cylinder engine shows a gain of 12 per cent, over the 6-cylinder Phantom II engine.

Apart from this a 12-cylinder engine is materially shorter than a 6-cylinder unit of the SaIllfs capacity. The wheel-base of the Phantom Ill measures 11 ft. 10 ins., as compared with the 12 ft. 6 ins. of the older car, the amount of space available for mounting the body remains unchanged. The new car is actually 2 inches shorter than the Continental shortchassis model, and an increased steeringlock and light steering make for. effortless driving in traffic and ease of manevuvring whether in confined spates or on the hairpins of an Alpine Pass. A well-designed system of independent suspension can be of the greatest ad

tage, especi;t1ly when traversing rough roads at speed, the improvement in springing being noticed particularly in the back seats, while another important point is that road-shocks are not communicated to the steering Wheel. It is interesting to notice that Messrs. RollsRoyce prefer to use semi-elliptic springs at the back, finding that it confers a steadiness often difficult to obtain when all the wheels are independently sprung.

A notable feature of the front springing is the fact that all working parts are enclosed.

In any survey of the new car the engine obviously comes first. The twelve cylinders are in two rows of six, forming a 60 degree vee, and their bore anti stroke are respectively 3i inches and 41 inches (82.6 mm. and 114.3 mm.) giving a capacity of 7,340 c.c. and an R.A.C. rating of 50.7 h.p.

The dominant feature of the engine is the rigid box-like casting of the crankcase. The water-jackets are cast integral with this, and the cylinders are in the form of hard steel liners which have their outside surfaces in contact with the cooling water.

Two valves per cylinder are carried in detachable aluminium heads, and these are operated by push-rods from a single cam-shaft carried in the vee between the cylinder-blocks. The tappets are in two parts, one fitting inside the other, and oil under pressure forces them apart and keeps the valve clearance at a constant figure. Two 14 mm. plugs are used for each cylinder, and there are two distributors and two coils mounted at the front end of the engine. There are two carburetters for each bank of cylinders and these are carried between the blocks and surmounted by a large air-cleaner and silencer. The carburetters, which are Rolls-Royce manufacture, are of the single-jet type with the orifice controlled

by a piston which moves in accordance with the depression in the induction pipe. In addition there is a small independent carburetter which supplies mixture for easy starting and slow running. The

petrol tank holds 33-gallons, and the carburetters are supplied by means of electric pumps. The crank-shaft is fully balanced and is carried in seven main bearings. The lubricating oil is pumped through a pres sure filter and then through a honeycomb cooler maintained at an even temperature

by the cooling water from the radiator. This latter is of characteristic Rolls-Royce design, somewhat wider and less high than on the Phantom II model, and is fitted with shutters controlled by a thermostat. The engine is mounted on rubber independently of the gear-box. The clutch is of the single dry-plate type, and is coupled up to the gear-box through two universal Joints. Constant-mesh pinions are used

for all the indirect gears and for reverse, and in addition synchro-mesh mechanism is fitted to second, third, and top gears. Torque reaction is taken by the back springs and so the propeller shaft is open, with needle-bearing universal joints at each end. The final drive is by hYpoid Spiral-bevel gears, which keep the propeller

shaft well below the floor level, and the fully floating back-axle is built up with that multiplicity of bolts and smoothness of contour which has always distinguished this part of a Rolls-Royce car. The chassis sweeps up from the front, is level amidships to form a rigid plat form for the main weight of the body and is carried in a gentle curve over the back axle. Immense strength is imparted to the side members by joining up the inner flanges to form girders of boxsection. A box-section cross member beneath the radiator gives the rigidity needed for independent suspension, and an X-member of large dimensions braces the structure between the engine and gearbox, but in spite of all this the chassis

shock-absorbers of the well-known RollsRoyce pattern are fitted and,. like those on the front suspension, their action can be varied by means of a small lever on the steering wheel. A stabiliser consisting of a torsion bar and connecting links further stiffens the rear suspension. The four-wheel brakes are applied by the familiar mechanical servo-motor

is actually 8 per cent. lighter than the one employed on the Phantom II.

Each front wheel is carried on two levers of ” wishbone ” formation, which swing in a plane not at right angle to the centre line of the chassis but slightly rearwards of this. In this way the track does not alter, nor does the car heel over when taking a corner. The motion of the upper lever is resisted by a helical spring carried horizontally and enclosed in an oil-filled chamber. This housing also contains the shock-absorber and the riding-control mechanism. The steering gear is of the worm and sector type mounted in the normal posi

tion. The two wheels are steered by means of transverse rods from a central bell-crank system carried in front of the engine. Long semi-elliptic springs are used for the back-axle, each leaf being ground to a perfect fit on its sliding surface. The spring gaiters are lubricated from the chassis lubrication system. Hydraulic

which is in fact a friction clutch driven by worm gears from the gear-box, and the pull is compensated by means of balance levers and miniature differential gears.

The wheelbase, as has been said, is, 11 ft. 10 ins., while the track is just over 5 feet. This allows of back seats 49 ins. wide, giving ample room for three people abreast without detracting from the appearance of the car. The chassis of the Phantom III costs £1,850, a Continental touring saloon is listed at £2,535, while the striking open sports touret depicted in the new catalogue is available at £2,510. The new catalogue incidentally is a beautiful production fully in keeping with England’s finest car.

The Phantom III has come at a time when the prestige of Great Britain is at its highest in the world of motor-cars, and will set the seal on the exhibits at Olympia, which are viewed by visitors. from every quarter of the globe.