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Aviation History
1918
1918 - 1258.PDF
NOVEMBER 7, 1918 to assist in heating the carburettors, which are also waterjacketed. The average thickness of the walls of the crank-chambetis 9 mm. i - * .; Base-Chamber1' ' The bottom half of the crank-chamber is complicated in•design, and excessively heavy, weighing 73.5 lbs., complete with false bottoms. The walls are 6 mm. thick, and are strengthened insideand out by ribs spaced 130 mm. apart. A perforated plate of galvanised sheet steel is screwed on toa^'flange cast about half-way down the chamber. This plate has shallow oil sumps formed on it at each end and a largehole cut in it in the centre ; other holes, 25 mm. in diameter, .are^pierced in it in various places. Over this bottom isscrewed a sheet of finely perforated steel, covered on the under- side with very fine wire gauze. Below the filter plate thebottom of the base chamber slopes sharply to the centre portion, which is flat and has a small sump bolted on under-neath it. Cooling ribs are cast on the two sloping portions, both inside and out; the sides of the base chamber are carrieddown 40 mm. below the bottom and a strip of sheet aluminium of a bronze worm wheel, which floats on a square formedon the plunger. The worm wheel is driven from the crank- shaft by a worm cut on a small inclined shaft. Besidesrotating, the plunger is made to reciprocate by means of a scroll cam machined in the plunger, which works againsta hardened steel roller fixed into the pump barrel, and thus transmits the reciprocating motion to the plunger, the endof which is plugged and forms the piston of the main pump. The small ram fitted inside is also hollow and works onthe same principle, though in this case the barrel moves whilst the ram remains stationary. A port cut in the sideof this small plunger is put in communication alternately with the supp'y pipe from the tank and the delivery pipe tothe camshaft, by means of an oil way drilled radially in the main plunger. From the main oil pump the oil is forcedalong a delivery pipe to the centre of the engine, where it feeds the main oil lead running beneath the crankshaft andconnected to each of the journals by vertical branch pipes. The crankshaft is bored and plugged in the usual mannerand conveys oil from the journals to the crank-pins, whence the oil is forced up the small pipes attached to the connectingrods into the little end bearings. Fig. 21.—Parts of oil pump. is screwed on to their lower edge, thus forming an air chamber along the whole underside of the engine. The aluminium plate has three air ports covered with wire gauze at each end. According to a report these ports are fitted with a vaned shutter. The main air supply for the carburettor is taken from this false bottom through a passage cast in the side of the crank- chamber. The purpose of the false bottom is to cool the lubricating oil and warm the incoming air. Oil Pump and Lubrication System The lubrication system of this engine is on the wet sumpprinciple, having one large pump to keep the main oil in circulation, and a smaller pump to supply a small chargeof fresh oil to the system at each pump stroke. In this engine the main pump sucks oil from the sump,which is approximately of seven gallons capacity, and delivers it under pressure to the main journal bearings. The small pump supplies the camshaft with fresh oil takenfrom the tank cast in the top half of the crankcase. The main oil pump consists of a steel plunger 40 mm. in diameter,working in a cast iron barrel. This plunger is hollow and pas another plunger or ram, 7 mm. in diameter, fitted insideit- Both the barrel of the pump and the small plunger remain stationary, whilst the large plunger is rotated by means The delivery pipe from the small pump to the camshaft istaken up the front end of the engine and runs along outside the camshaft casing, being connected to the oil ways drilledin the cover plates by six inclined channels formed in the cover plates, as shown in the photograph, Fig. 10. From this central oil lead in the cover plates the oil isconveyed to the camshaft bearings by the vertical holes drilled in the ends of the cover plates, and to the inner rockerarms by short cross channels, which deliver the oil into grooves milled in the rocker arms, whence it finds its way to thejournals of the hollow rocker spindles and their bearings and also to the cam rollers and cams. The camshaft casing is always kept half full of oil, and pro-vision is made for filling up before starting by three holes fitted with screwed plugs, which are placed in the top of thecover plates. From the camshaft casing the oil overflows through twogrooves formed in the side of the front camshaft bearing, and thence finds its way to the sump down the verticalspindle casing, lubricating the vertical spindle bearings and gears on its way. The oil sump is exceptionally deep, and is fed from thesheet steel false bottom by three pipes, one from each end and one from the centre. (To be concluded.) I259
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