THOUGH described in The Motor Cycle immediately after its success in the 350 c.c. class of the French Grand Prix, a further reference to the unconventional Garelli two-stroke cannot fail to be of interest, especially as the makers are now represented in England.
Few examples of departures from accepted practise, such as the Garelli is, have attained success at the very out-set of their careers, but with this machine success was obtained not only in the small field at Strasbourg but in a much larger and more dangerous one of 39 riders on the Monza track in the Gran Premio delle Nazioni. It must be mentioned here that the engine design is not actually novel and owed its origin to an English inventor, but the Cavaliere Garelli was the first to adapt the principle to a motor cycle engine.
Two Pistons on One Rod.
Briefly the Garelli engine (50x89 mm.) has two cylinders with clear air space between, two pistons and a common combustion chamber. Of the two pistons which are of chrome nickel steel the right-hand one has a flat top and the left-hand one a domed top, which acts as a deflector and prevents turbulence. These pistons, which are, of necessity, very long, are connected at their base by a single gudgeon pin in the centre of which works the small end of the single connecting rod.
On the mixture supplied by a one-lever Zenith carburetter (fitted with additional extra air inlet) being drawn into the crank case and compressed, the transfer port, which is inside the cylinder (actually in the dividing wall between the two) is uncovered by the left-hand piston, fills the left-hand cylinder and the combustion chamber and helps to excel the residue of burnt gases in the right-hand cylinder as the exhaust port is still uncovered; the pistons then rise and compress the charge which is fired by the plug in the left-hand cylinder, but as there is a common combustion chamber both pistons receive the explosion pressure.
Following the tendencies of modern Italian design unit construction is followed, but otherwise the lower part of the engine follows standard two-stroke practice in the main, but there are two inside flywheels, one of which incorporates a most ingenious transmission shock absorber.
A star-shaped piece forms part of the main shaft and between the points of the stars there engage corresponding spring-loaded plungers, which work in steel bushes in the flywheel of the racing engine, while in the touring engine ball a disc clutch absorber is employed.
Particular mention should be made of the clutch, whiich is of the multi-disc variety and is entirely enclosed in the unit, which, of course, contains the first reduction gear by spur wheels and the change speed gears.
Magneto Completely Enclosed
Equally as neat as the clutch is the Mea-Garelli magneto, which is likewise entirely enclosed in the unit, but is easily detachable therefrom.
The result of this design is that the whole of the mechanism is enclosed and the only visible moving part is the final transmission chain.
Not the least interesting part of the machine is the internal expanding brake in the back hub, which possesses two sets of shoes, with the result that two independent brakes are incorporated in the one shell, each separately controlled.
Detachable wheels are fitted, and the front forks, which are of a special design, are extraordinarily flexible.
All controls are entirely enclosed, no naked wires being visible, while the change speed lever acts directly on the gear box, there being no intermediate toggles or rods.
Owing to the high-class finish and the fact that there is a heavy import duty on the machine the price is high, being £135.
Now that the Garelli has arrived in England its road performances will be as eagerly awaited as its victories in races were acclaimed in the most important Continental events during the past season.
A. F. Lago, Ltd., 2. Featherstone Buildings, High Holborn, London, W.C.I, are handling the machine.
The Motor Cycle December 7th, 1922.