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Aviation History
1918
1918 - 0593.PDF
MAY 30, 1918. THE 24O H.P. (8-CYLINDER) MERCEDES. (Continued from page 562.) Connecting Rods. THE H'section connecting rods and floating small- end^ bushes are similar to those used on the 160 h.p. engines except that the big-end bearings are 3.5 mm. shorter in the 8-cylinder engines. This reduction in the length of the big-end bearings has been effected by turning off the outer faces of the connecting-rod are cast integrally with the bottom half of the base- chamber, and, as usual, are secured by long bolts passing through the top half of the crank-chamber, and acting as the holding down bolts for the cylinders. Following the usual Mercedes practice the crank webs are made slightly heavier in cross section towards the front end of the crankshaft. The external diameter big-end brasses, evidently with the idea of reducing of the crank pins is 55.9 mm., and the length of the as much as possible the overall length of the engine. Crankshaft. f The exceptional length of the crankshaft and the disposition of the cranks is shown in Fig. 10. The crankshaft runs in 9 plain white metal bearings, and isjitted/with a thrust ball-race at the front, at which pins 70 mm. The decreasing internal diameters of the hollow crank pins and journals follow the Standard Mer- cedes practice, the holes bored in the rear end crank pins and journals being 40 mm., whereas the internal Fig. 8. end the driving pinion is supported by a large ball- bearing, mounted on an extension of the driving pinion. The firing sequence occurs alternately through the first and last sets of four cylinders, i.e., 1, 3, 2, 4, 8, 6, 7, 5. It will be noticed that numbers 1 and 2 cranks are at 1800 to each other, as are the cranks Nos. 7 and 8, whilst cranks 3 and 4, 5 and 6 are also set at 1800 to each other respectively, but are at 900 to the front and rear pair of cranks. The external diameter of all the journal bearings is 55.9 mm. The length of the front bearing, next to the reduction gear, is 90 mm. ; all the other journal bearings are 56 mm. long, with the exception of the rear bearing, which is 80 mm. long. The bottom halves of the main bearing housings Fig. 9. diameters of the crank pins and journals are gradually reduced throughout the length of the crankshaft to 22 mm. at the front end. The thrust ball race at the front end of the crank- shaft is situated directly behind the reduction gear pinion, and is held in position in the two halves of the crankchamber housing, the thrust race being located by a double flanged ring, and also by a split bush and gunmetal collar on the crankshaft. Full details of the crankshaft design are given in Fig. 11. Reduction Gear. In view of the fact that this engine is apparently the first attempt to introduce an indirect propeller drive on any enemy aero-engine in service, the con- struction of the reduction gears, as fitted to the
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