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Aviation History
1918
1918 - 0686.PDF
are! interchangeable as in the 160 h.p. engines and are of similar design ; the valve operating gear is, however, of new design, and follows more the construction of the valve gear on the 260 h.p. Mercedes engines. General details of this construction and working of the valve gear shown in the sketch, Fig. 4. . It will be noticed that the rocker arms and their spindles are now integral, being machined from steel forgings. The camshaft casing is constructed entirely from malleable-ircn Fig. 5.—Section of carburettor (semi-diagrammatic). castings, and the valve rocker spindles work in direct contact with ths malleable-iron, no bronze bushes being provided as bjarings for the rocker arm spindles, and the covers of th2 camshaft casing form the top portion of the rocker spindle bearings. The rocker spindles are hollow, and are lubricated through two Tholes drilled radially ia the spindles by oil thrown off the revolving cams into the two holes drilled in the rocker arm carrying the cam roller. This design of valve gear is undoubtedly a great improve- m2nt on the arrangement adopted in the 160 h.p. Mercedes, the construction of which is well known, having the rocker arms working through slots in the camshaft casing, which are provided with felt-packing strips and baffle plates for re- taining the oil in the camshaft casing. Camshaft, The camshaft is of similar design to the 160 h.p. Mercedes, and the casing is supported on long studs which are screwed into the head of each cylinder. ••^With regard to the valve timing, this, it will be noticed, is different from the standard 160 h.p. Mercedes, as shown in the comparative list of leading particulars. The valve lift has been increased from 0.440 in. on the 160 h.p. engines to 0.452 in. Only very minor differences occur in the actual dimensional details of the half compression gear in the new engine. Details of this mechanism are now well known ; the general design is, however, clearly shown in the general arrangement sectional drawing of the engine, Fig. 3. Carburettors. No alteration has been made in the design of the twin-jet dual carburettors. Both carburettors are enclosed in a cast aluminium water jacket, which is coupled at the bottom by a water pipe to the delivery pipe of the water pump at the top of the water jacket of the rear cylinder to the top portion of the water jacket of the carburettors, as shown in Fig. I. Each carburettor feeds three cylinders by a branched induc- JUNE 20, 1918. tion pipe of "steel tube which is lagged with asbestos cord and bound with adhesive tape. The throttles are, of course, intercon- nected, and are operated by a cable and also by a con- trol lever and rod. The float chambers are of ordinary de- sign, but are fitted with separate niters attached to the bottom of each float chamber, which are easily detachable. These niters are provided with needle-valve drain cocks. No compen- sation arrangement is provided for alti- tude control. The bore of the main jets is 1,473 mm., and the bore of the pilot jets, .558 mm., which is the same as in the 160 h.p. Mercedes carburet- tors. A semi- diagrammatic sec- tional view of one of these carbu- rettors is repro- duced in Fig. 5, for reference. r^The air-intake to the carburettors is taken through the passage cast in the central portion of the top and bottom halves of the base- chamber, which forms an air chamber between the front and rear oil pumps in the lower portion oi the bottom half of the base. Air enters the central air chamber through two holes cast in the sides of the chamber and also warm air through a large diameter pipe leading from the central portion of the tophalf of the crank-chamber. Camshaft Drive. The'method of fixing the camshaft driving bevel at the top end^of the vertical shaft, as shown in the sketch, Fig. 6, is r^: Fig. 6 Method of attaching the camshaft driving pinion to the top end of the vertical driving shaft, and the arrangement of the Skefko twin race ball bearing on bottom end of vertical shaft. From ouxil'Cy Sumpf Rerurn to Oil TOOK Fig. 7.—Diagrammatic section of oil pump. 684 J
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