IT has long been a source of wonder to motor cyclists that the sleeve valve engine has not been adapted to motor bicycles. In the motor car world, the Daimler, Panhard, and Minerva cars are fitted with sleeve valve engines made under the Knight patents, their licences to manufacture dating from ten years |back, while the famous car of Swiss make, the Piccard Pictet, has a somewhat similar engine made under a British patent. 'Yet up to the present time little has been heard of an engine of this pattern being made of a size and type suitable for the popular little vehicle in which this journal lis especially interested. It may be argued that the poppet valve engine universally fitted to motor cycles is so satisfactory that nothing better is required. That it possesses reliability, keeps cool, maintains and gives off its power, is an argument which may be put forward by many.
Yet there is something wanting, something we have advocated for years, and that is 'silence. To silence the exhaust is not difficult, but to render innocuous the xattle and din proceeding from valves, cams, and timing wheels is not easy without interfering with the efficiency of the engine. We want rapid valve opening, Tapid closing, large valves, and a fairly high lift so as to get the utmost out of our small engines, and to get all these we have to put up with a certain amount of noise. Such noises are more wearing to the nerves on a long run than the regular patter of the exhaust. The solo rider suffers from the complaint, and the passenger in the sidecar fares worse, as the .sidecar body acts as a sounding board.
Advantages of the Sleeve Valve.
Now the sleeve valve engine has no valve noises. It can equal the poppet engine as regards power, it needs less attention as there are no seatings to be ground, and if it be proved that the moving parts wear well and that the sleeves do not seize it has a future before it which is full of promise.
It is most gratifying to be able to make the first announcement that Messrs. Barr and Stroud, Anniesland, Glasgow, have turned their attention to an engine of this type, which is already emerging from the experimental stage. This firm is, of course, well known to those of our readers who have served, or are serving, with the Navy, the Army, and the R.A.F., as it is world famous for the production of instruments demanding such accuracy of manufacture as range finders for all three arms. of the Service, and fire control apparatus for His Majesty's ships.
Inlet and Exhaust.
The Barr and Stroud engine is the first air-cooled, single sleeve valve motor the making of which is to be taken up seriously. It is made under the Burt and McCallum patents, which cover the engines formerly fitted to the Argyll car, and now used on the Piccard Pictet. The bore and stroke respectively are 70 x 75 mm. (290 c.c), and the engine is rated at 2 1/2 h.p.
Its cylinder is of aluminium, blacked so as to aid radiation, and near the top is cast an annular induction space, in which there are four inlet ports admitting explosive mixture via an inlet pipe set at 45 degrees to the fore and aft line of the engine, so that the< mixture is equally distributed to each pair of ports.
The fact of the induction space being so near the top of the cylinders helps to keep the detachable head cool. In its present form the two pairs of exhaust ports are connected by two aluminium castings on each side of the cylinder, which, in turn, are connected by a Y shaped exhaust pipe, the stem of the Y being below the down tube of the motor bicycle frame. Both inlet and exhaust ports, which are of peculiar shape, are covered and uncovered by means of a single sleeve, having a dual function, as it serves to do the work of both inlet and exhaust valves, and also acts as a cast-iron liner for the aluminium cylinder.
So far as the distribution gear is concerned, this is of more or less standard pattern, consisting of the usual train of wheels, but the engine shaft is so splined that the pinion can be fitted only in the correct position.
What would be the camshaft on an ordinary engine is a short shaft carrying two eccentrics, of which that nearest the timing wheel imparts an oscillating motion to the oil pump, while that on the further end of the shaft may be tnore correctly designated as a crank disc ; the crank pin passes through one end of a link, the other end being
The engine does not appear extremely unconventional attached to the sleeve by means of lugs at the top and bottom. The rotary motion imparted by this crank disc causes the sleeve to rise, and at the same time the link is forced outwards along the crank pin. Thus the sleeve is lifted about one inch and simultaneously turned about forty-five degrees. This action causes a very rapid opening and closing of the ports, as it happens when the speed of the sleeve is at its highest point. Consequently, the maximum efficiency should be obtained.
Inside the sleeve works the aluminium alloy piston, possessing two rings at the top and a drilled groove at the base so as to allow any excess of oil to escape. There is nothing very special in its design, except that inside in the centre of the head a small pyramidical point is cast dead over the oil hole in the connecting rod small end, so that oil drips exactly in the place where it is most wanted, and this device, we are told, is most effective.
Aeroplane engine practice is adopted so far as the gudgeon-pin fastening is concerned, as this is secured by means of a split wire ring sprung into a groove. The connecting rod is of high quality steel, and is provided with a split big end, while the crankshaft is of the solid variety of special steel provided with balance weights and drilled for lubrication.
We now come to the oiling system. Reference has already been made to an eccentric on the sleeve-operating shaft driving the oil pump. This latter is of the plunger type, of which tlie plunger works in a vertical brass barrel with a :ball non-return valve at its base secured inside the crank case. The function of the pump is to deliver oil from a reservoir under pressure to the off side main bearing. Leakage from this bearing supplies oil to the timing gear, lubricant being carried up the train of wheels, and any excess being drawn off by suction on the up-stroke of the piston, through a non-return valve in the crank case. After being forced through the off side main bearing, the oil passes through the hollow crankshaft and issues through a hole in the crank pin lubricating the big end, it being flung therefrom on to the walls of the sleeve. The oil then passes to the near side main bearing, and any excess in the crank case is forced through a non- return valve at its base by the descending piston back to the reservoir.
The detachable cylinder head is of aluminium, hemispherical in shape, having a cast iron bearing for the sleeve, and carries the sparking plug and a mushroom relief valve, as no exhaust valve lifter is, of course, possible in an engine of this kind. This release valve is to be connected to the exhaust port, so that no noise occurs when it is brought into operation. The head is held in the cylinder by means of a castellated ring.
In outward appearance the engine strongly resembles a two-stroke, chiefly owing to the absence of valves and to the position of the exhaust port castings, while the illusion is still further aided by the fact that it has an outside flywheel, which in future models will be on the transmission side of the engine.
On the Road.
After a careful examination of the engine and its parts, we were privileged to make our first trial trip on an air-cooled sleeve valve engined motor bicycle. The bicycle to which the engine was fitted was of well-known make, fitted with chain-cum-belt transmission and a two-speed gear.
In cold and damp weather, a run of about fourteen miles was made over fair roads of an undulating nature, including one fairly steep hill. An Amac carburetter was fitted, which was provided with so small a jet that the air lever could not be used, and it was therefore, to all intents and purposes, of the single lever variety. An attempt to start by paddling off on a slight up grade presented no difficulty, as the engine fired at once. With a view to testing the engine severely, and owing to the greasy nature of the road, no attempt was made to change into high gear for some time. Once clear of the bad road, the speed was increased, and no incident occurred until one of the firm's experimental staff who accompanied us led the way up a steep hill which could not be rushed.
This was taken on low gear and with the throttle fully opened, but on reaching the summit the high gear was engaged without a falter, and throughout the run not a sign of a "konk" could be detected, and the engine kept remarkably cool. The next rise the engine took on top gear in excellent style, and thereafter followed a certain amount of straight road, on which a good pace was obtained. Although the makers admitted that the balance could be improved, we noticed very little to complain of in this respect, but we were truly sorry that the exhaust silencing arrangements were somewhat crude.
This fact prevented us from appreciating that the engine, apart from exhaust explosions, was really quiet, and only when throttled right down could the silence of the engine be adequately realised. There was no silencer proper, merely a long exhaust pipe with a flattened end, but when throttled right down or descending a hill nothing but a muffled swish could be noticed.
The engine may be said to have emerged from its experimental stage, but at the present moment its makers are not prepared to make any statement either as regards its delivery or its production, nor are they prepared to answer any correspondence concerning it. We hope, however, to be able to make further announcements at an early date. In our opinion, the engine shows great promise. We tried hard to seize it up, but it refused to oblige us, and we believe that in its present form as a small single-cylinder, as a large V twin, or as a moderate power flat twin, it has great possibilities.
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