Novel Design of Twin-cylinder Two-stroke.
FOR some time past there have been rumours of a twin two-stroke to be produced by the Premier Cycle Co., of Coventry, but, though we were permitted to have. a private view of the experimental mode some months ago, it was not until this week that we have been able to give preliminary details of what is likely to prove the most startling novelty of the year. The new Premier is unorthodox in almost every feature, but this must not lead readers to think that it is untried, for it has undergone prolonged tests with the most satisfactory results, and the design, though unusual, is clever, and may lead to striking result in the near future.
A Very Novel Engine.
The engine is a twin vertical two stroke, with the crankshaft set longitudinally in the frame. It has a capacity of 322 c.c. (bore and stroke 64x50 mm.) There are no connecting rods in the usual sense of the term, but vertical piston rods working in long guides are fixed solidly to the piston head.
At the base of these rods a flat foot is formed, and set on a radius. The foot is carried in a white metal T section guide formed solid with the top half of the split big end bearing. Thus, when the crank is rotated, the piston rod moves vertically, while the curve of the plate or foot imparts a slight rotary action to piston. This action is utilised to open and close the ports for the various processes of suction, transfer, and exhaust. The space between the piston walls and piston rod guide is filled by an aluminium casting, and the inlet port draws gas from an automatic carburetter during almost the whole of the upstroke of the piston, instead of for the short period when the piston nears the top, as in most two-strokes.
On the piston descending, the induced gas is compressed in a cast aluminium receiver bolted to the cylinder, and thence is transferred to the combustion space via the cylinder head and baffle plate. The piston head is stepped on both sides of the baffle, the steps being arranged so as to make full use of the rotary movement of the piston. At the back of the balanced crankshaft lies a plunger pump, which forces oil from a sump in the crank case through the crankshaft to the big ends and piston rod slides, the oil passing through the centre of the pump plunger into the crankshaft. The guides and pistons are amply lubricated by splash, as the suction below the piston helps to raise the oil. Ball bearings carry the crankshaft at each end.
The Gear Box and Transmission.
Directly behind the crank case lies a pair of skew gears which drive the main gearshaft at right angles to the crankshaft. The three-speed gear has all its pinions constantly in mesh, and each gear is forked to the shaft as required by a central wedge bar, which expands balls against the inner face of the gear wheels in a similar manner to the well tried lathe gear. The final drive is by belt.
Even the frame is unusual, for all the head and saddle tube lugs for the duplex frame are cast with two circular bodies, which form the front and back ends of the combined tank and top frame tubes the two ends being brazed to a large diameter steel tube.
Both brakes are of the internal expanding type and lie side by side in the rear hub, the hubs themselves being mounted on journal ball bearings. The equipment is full and on standard lines, and it is likely that one model will be turned out in a biscuit colour with no plated parts, which gives an extremely smart finish. Incidentally, one of the latest 3½ machines finished as above was shown to us.
The standard models have undergone but little alteration. Both 3½ and 7 h.p. will be fitted with twin internal expanding brakes, and the 7 h.p. has steel flywheels stamped from the solid with the crankshaft. Special attention has been given to the prevention of oil leakage.
The Motor Cycle, November 19th. 1914. p569
Engine, Three-speed Gear, and Magneto forming a Single Unit.
In the "Buyers' Guide" issue of The Motor Cycle we were enabled to give the first details and sketches of the new Premier twin two-stroke, and by reason of its novel and striking design great interest has been evinced by all interested in motor cycles.
The twin engine, which is built under Alfton's patents, is now undergoing tests. In this issue we are enabled to publish illustrations of the power unit and frame; the latter are strikingly unusual both in detail and in general design. The compactness of the unit will be clearly seen from the photographs. In front, is mounted the outside flywheel; then come the two cylinders set longitudinally and operating the crankshaft through vertical piston rods and curved foot plates.
Forced Feed Lubrication.
At the back of the crankshaft the plunger oil pump is driven from an eccentric, and forces oil to the big ends and foot plate slides, and behind this again lies a pair of worm wheels driving the counter-shaft three-speed gear. This gear is very neat, and occupies an extremely small space, as the gears are only just separated, and are brought into action by a central shaft arranged so as to expand steel balls against the inner periphery of the pinions, thus locking them to the driving-shaft in turn. To prevent any possibility of the gears slipping out of position a simple and positive form of spring plunger is arranged, and the control rod from the tank operates through a squared joint giving just sufficient freedom of movement. Finally, the magneto is mounted at the rear of the unit, and is driven direct from the crankshaft. Except for the piston rod bearings and slides, ball bearings are used throughout, and careful provision has been made for the prevention of oil leaks, a screwed washer mounted on the shaft returning any excess of oil to the sump.
The special receivers in which the gas is compressed can be clearly seen, and also the expansion chambers, which are attached direct to the exhaust ports, and permit the burnt charge to expand before being led to the large silencer directly in front of the engine. These expansion chambers will, in the final design, be fitted with cooling ribs.
Operation of Compression Release Valves
The compression release valves are very simply operated. for a straight bar is mounted in guides directly over the valve in each cylinder head. A taper is formed with its smallest diameter kept normally over the valve stem by a spring. By means of a Bowden control the bar can be moved horizontally so that the tapers engage the valve stems and release the gas.
The principle of the duplex frame with its top tube tank has already been described. It may be remembered that both brakes are of the internal expanding type mounted in the rear hub. The mudguarding is excellent, and the rear guard is attached to a combined pressed steel carrier and tool box. The frame is extremely low, and the absence of tubes above and below the tank renders the machine particularly easy to clean.
The machine is the most novel and interesting medium weight we have yet seen, and we are looking forward with considerable interest to a road trial in the near future. We shall then hope to refer to the new Premier again.
The Motor Cycle, December 10th. 1914 p661