A NEW BRITISH BIG TWIN.
The Sporting Duzmo, with Overhead Valves.
IN placing the new 1000cc twin Duzmo on the market, the manufacturers are making a direct appeal to the sporting section of riders to whom power, speed, and flexibility are great attractions. It has often been stated that this section of the public has no wide choice of British machines ; thus the new Duzmo will be an attractive addition to the high-powered solo class. The cylinders closely resemble that of the single-cylinder model which competed in the A.C.U. Six Days Trials. Having a bore and stroke of 89x79 mm., the cylinders are set at an inclined angle of 50°.
Detachable heads, held down by long bolts, and machined all over internally, are employed ; and the arrangement of the overhead valves is such that there is a total absence of pocketing, the rocker gear being supported from lugs cast integrally with the head. In the case of the forward cylinder, the exhaust pipe curves neatly round, and terminates in a drilled fish-tail extending well beyond the rear spindle on the near side, while the rear exhaust pipe is brought straightaway to the off side of the machine. Lubrication is by means of a Best and Lloyd mechanical pump, and, in addition, an auxiliary hand pump is fitted. There is a separate oil lead to the back of the front cylinder.
A separate camshaft is utilised to operate the valves of each cylinder, and the whole of the exhaust lifting gear is enclosed within the timing cover. An interesting innovation in this respect is an arrangement by which the front exhaust valve is raised before the rear valve, so that the risk of oiling up the rear plug is lessened. Articulated connecting rods are used — a feature which is unconventional as far as motor cycle engines are concerned, although common practice in aircraft.
The rear connecting rod has a large roller bearing big-end, and close above the bearing is a lug and pin to which the forwar'd connecting rod is attached. Floating both in piston bosses and small ends, the gudgeon pins are located by spring split rings, the pistons themselves being of aluminium, and of more or less conventional design.
Precautions against Valve Breakage.
We were informed that no trouble has been experienced with broken valves falling into the cylinder and causing damage to the piston and cylinder head. In this connection the valve gear is so arranged that, unless the fracture occurs close up to the head, the valve cannot drop into the cylinder. Stainless steel is used in the valve construction, and is giving every satisfaction. The finish of the engine is excellent, and the appearance most attractive.
Transmission is by chain throughout, a Sturmey-Archer three-speed gear providing the necessary change of ratios. Rear braking is carried out by means of a shoe operating on a dummy belt rim, and a Webb internal brake is incorporated in the front wheel. Wide petrol tank, straight handle-bars, and narrow mudguards provide a very sporting appearance to the macliine; though, in the case of the touring model, ample mudguards are provided, and it has an expansion chamber of generous dimensions.
Brampton forks and a Brooks racing saddle are fitted, and in conjunction with conveniently placed footrests, the riding position and general controllability are distinctly good.
Single Lever Carburetter Standard.
Such excellent results have been obtained from the Cox-Atmos sinle-lever carburetter on test that this device will be standardised.
Whether the new Duzmo will succeed in attaining a 100 m.p.h. gait on the track or not, its performance in competitions will be watched with interest.
Mr. J. Wallace, the designer, is confident that the new model will cater for a market which undoubtedly exists, and his confidence should be justified. The Duzmo is being manufactured at Cedar Road, Enfield Highway, Middlesex.
Sources: The Motor Cycle
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