A French Machine with "Side-by-side " Twin Engine and many Other Innovations.
SINCE our brief inspection of the Viratelle - an interesting machine of French origin (a description of which appeared in the issue of December 9th) - M. Viratelle, whose name it bears, gave us a demonstration of its road performance. It may be recalled that the Viratelle is a water-cooled four-stroke machine, one model of which has two cylinders side-by-side; and as no similar motor cycle is on the British market its running was of particular interest. Probably the side-by-side twin is the neatest form of two-cylinder engine, and the reason why four-stroke engines of this type have not been more greatly favoured is on account of (1) the difficulty of balancing them if even impulse torque is obtained by arranging the cranks at 360°, and (2) the uneven firing torque if good mechanical balance is secured by using cranks at 180°.
We have had both types in the small car field, and excellent examples are still giving satisfactory service. The 8 h.p. Perry has the 360° crank arrangement, and the engines of the 7 h.p. Swift and 8 h.p. G.W.K. have cranks set at 180°. Owners of the first mentioned car will tell us that the vibration set up by the 360° setting is imperceptible, while Swift and G.W.K. enthusiasts state that there is no inconvenience or irritation accruing from the uneven firing, i.e., two explosions in one revolution and none in the next. The two-cylinder Viratelle engine is of the Perry type, and is, therefore, artificially balanced, as, say, two single-cylinder engines placed side-by-side. One would suppose that, as the pistons move in unison, vibration would be present, but, after our trial of the French machine, we must admit that these theoretical objections are not so serious as is generally thought.
Unfortunately, a sidecar body was unavailable ; consequently it was impossible to appreciate the comfort provided by the long laminated spring, which supports the bearers of the Viratelle chassis.
Perched on the carrier, however, which is incidentally abnormally wide, we were able to follow with interest the ease with which the machine is controlled. Starting is effected by inserting a detachable handle, which is neatly clipped to the carrier stays, into a recess at the front end of the transmission case. The engine responded immediately to a half turn of the starter, and, with the first gear engaged, a touch of the clutch pedal, which, since the gear is of the epicyclic type, is actually a brake, set the machine in motion.
The transmission is smooth, whilst the silence of the engine was quite car-like. The gears are engaged by moving a small lever on the handle-bars, and it is possible to prepare a gear ratio long before it is required. To bring it into direct engagement, the clutch is operated.
Responsive Gear Changing.
This scheme has a unique advantage, and would permit a change to a lower gear at the precise moment of advantage when ascending difficult gradients. The slow running of the engine is also worthy of note, and M. Viratelle demonstrated the working the front wheel within three inches of a slow moving vehicle. The efficiency of the radiator requires no comment, and the cylinders kept remarkably cool. The 3 h.p. single-cylinder model runs quite as well as the big machine, and hauls a light sidecar with ease.
It is hoped that these machines may have an opportunity of figuring in some open competitions, when their performance under difficult conditions would excite much interest.
The Motor Cycle, February 3rd, 1921, pp 126, 127.
