SOM THING NEW IN MOTOR-CYCLES First Details of Remarkable Ariel “Four.”

ASATISFACTORY four-cylinder motor cycle has been from very early days, the desire of a large number of riders, and the aim of more than a few designers. But the inherent qualities of the four-cylinder power unit of smoothness of torque and quietness were, so far as early attempts are concerned, rather heavily outweighed by cooling, carburation and installation difficulties. In the few examples which have been on the market in more recent years overheating and carburation troubles have been overcome, but there still remained the drawbacks of excessive wheelbase, weight distribution and questions of frame design. Hence, the reason for the ” four ” remaining in the background, while the allconquering single has gone forward in design and achievement.

With the introduction of a” four” devised on entirely new lines by the Ariel concern however, it is safe to say that there is a good likelihood of the multi-cylindered motor-cycle becoming established as a popular type before very long.

It was only in the past few weeks that news went round that this machine was to be marketed, and the details here given are, in point of fact, the first to be released by its manufacturers.

500 c.c. Known as the “Square Four,” the new Ariel is of 500 c.c. The engine layout is exceedingly interesting and embodies entirely new principles. In place of the usual ” inline ” or ” double-flat-twin ” arrangement of other designs, the cylinders are arranged so that in effect the power unit consists of two vertical twins geared to a common driving shaft. There are two crankshafts, gear-coupled and mounted on large diameter ball bearings. The main coupling gears are of specially developed tooth form, so that noise and back-lash are eliminated, and they run in a separate oil-fed chamber situated within the crankcase. The cylinders are cast et; bloc, with a detachable head, which has the

exhaust passages, and a radial induction manifold integral_ in the casting. All valves are in the head, and they are operated by the camshaft direct through rockers, the whole being totally enclosed by an aluminium casting, fitted with an inspection cover. The camshaft and magneto are both driven by a chain which is automatically kept at the desired tension. The conconnecting rods which are of light, high-tensile steel, run on substantial roller bearings at the big ends.

The lubrication system has been very carefully arranged. Employing two gear-pumps it is of the drysump type.

A single Amal carburetter (with twist-grip control) supplies the mixture and ignition is by a very compact Lucas magneto.

The drive from the engine to the rear wheel is by the usual primary and final chain arrangement. The gearbox is a fine job made specially for the machine by Messrs. Burman. It has four speeds, and a four-plate cork-inset clutch with a shock absorber. The box is supported by a frame member below, and not hung, and the whole can be swivelled so as to give a very simple and quick adjustment for the countershaft chain. The frame, which is a particularly robust piece of work, is of the duplex

cradle type, built from solid steel forgings and aircraft quality tubing. The front forks are tubular girder with central compression spring and adjustable dampers. Both front and rear wheels have taper roller bearings and brake drums of 7 inches diameter. The petrol tank is of typical Ariel pattern and has a 21 gallons capacity. Mounted in the forward end is an attractive instrument panel, very neat and balanced in appearance. It carries a Smith’s 100 m.p.h. speedometer, a Smith’s 8-day clock, an oil pressure gauge, and embraces the very large quick-release petrol filler cap. The whole is illuminated at night by a concealed bulb, which is incorporated in the lighting set. Current is supplied by a 6-volt Lucas magdyno and an accumulator;

The whole layout of the “Square Four ” is amazingly compact, and at first glance it is easy to mistake it for a single cylinder machine, as it has a normal wheel-base and the power unit is practically devoid of excrescences.

At the time of writing, we have not yet had an opportunity of trying out this most interesting motor cycle. But we can vouch for the fact that the engine is astoundingly silent, a ” revver ” and dead smooth. With full equipment it is to be marketed at £75 10s.