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A SPRING FRAME COMBINED WITH A SLIDING WHEEL.
ONE of the pioneer designers of the spring frame in the motor cycle world is Mr. F. W. Barnes, the works manager of Messrs. Zenith Motors, Ltd., Hampton Court, Middlesex. His first effort was the Zenette, the two side members of the frame being designed scissors fashion, each portion being separated from the other by coil springs.
The idea was ingenious, and worked well, but the design in those early days (1908) was crude. The new Zenith spring frame follows the very latest practice, is simple, by no means unsightly in appearance, and most effective. Two long leaf springs are employed, the forward ends of which are attached to the rigid portion of the frame, while the rearmost ends are attached to brass plungers sliding in the tubes of the movable portion.
This lower or movable portion, to which the rear wheel is attached, is connected to the rigid part by means of hinges attached to brass plungers sliding in the rigid tubes. The wheel, therefore, is free to move vertically, and to slide backwards and forwards, so as to preserve a constant belt tension in spite of the opening or closing of the expanding pulley on the engine-shaft.
Great improvement in appearance has been brought about by fixing the mudguard stays, mudguard, and carrier to the movable portion of the frame, so that they all move in unison with the wheel, and consequently there is not that ugly gap between the rear mudguard and the wheel at present to be seen in the Zenith when the highest gear is in engagement.
An Ingenious Self-adjusting Brake.
The sidecar attachment, which on an ordinary machine would be a clamp fixed to the near side chain stay, is a casting slipped over the spring and pushed forward as far as it will go. This is quite secure, and just allows of sufficient movement of this portion of the spring, which is, of course, very slight at this point.
Another important innovation is the new method of operating the rear brake by means of a rod instead of a Bowden wire, a piece of designing which was by no means easy to carry out in the case of a machine in which the back wheel is free to slide backwards and forwards.
The difficulty has been got over in the following manner. The long pedal operating the brake is provided with a stop, so that it flies back into the correct, position, and is connected to a long rod curved upward at its rearmost end and hinged to a point close to the rear spindle. This flat rod or bar passes through an adjustable yoke, in which there is a roller engaging with the bar. On the pedal being depressed the bar is lifted, presses the adjustable yoke upwards, which is connected to the brake shoe, and brings it up against the belt rim. This brake shoe is self-adjusting, an excellent feature of the Zenith brake, which has been in use for some little time, and allows the shoe to have a perfectly parallel motion, thus engaging the rim evenly and exerting the maximum degree of stopping power.
This device was seen more clearly on a 4 h.p. Zenith (85.8 mm. x 85 mm.), which was built to the order of the Russian Government. It was a standard clutch model, but possessed the important improvement just described. On this machine the instructions on the clutch, "Oil here freely," are written in Russian as well as in English, and this is the case also with the instructions as regards the operation of the gear, which are to be found on the top of the tank.
An interesting experiment we noticed in the Zenith Works was a pair of channel steel forks, which are much lighter than the ordinary forks, stronger, and on account of their smoothness in design, far more easy to clean. Though engaged mainly on war work. Zenith Motors are not neglecting their experimental department, and when new machines may be freely delivered the post-war model will be a thoroughly up-to-date machine, but in no way an untried model.
We had a very enjoyable little run on the 8 h.p. spring frame combination, and were greatly impressed by the smoothness with which it rode. Shortly after leaving the works, Mr. Barnes, who was riding in the sidecar, asked us to be sure and keep well in the centre of the road, so that we could drive over the maximum number of pot-holes, and at the end of that particular stretch we were compelled to ask him where the pot-holes were; they were certainly not noticeable. The machine was tried over varying road surfaces, and certainly up to the present it is one of the best sprung frames we have ridden. Naturally over exceptionally bad surfaces there was a good deal of motion, but all small indentations are entirely absorbed by the springs and are not noticeable, while the larger ones, though they threw the rider about, certainly eliminated the severe shocks which on an unsprung machine would be quite unbearable.
The Motor Cycle November 16th, 1916. Page 435