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shaft and in the starter and accessory driveshaft. The latter part is case hardened as shown in Fig. 6. It is suggested that this may well be a compromise for making the best possible use of the available scrap materials.

Propeller reduction gears, cam, and knuckle pins are carburizing 4.5 percent nickel steel plus approximately 0.8 percent chromium. Reduction-gear pinions vary form this composition in the addition of 0.4 percent molybdenum. Nitriding is used only in the cylinder barrel (fig. 7). The steel conforms very closely to AMS 6470. Nitride depth is 0.010 to 0.020 in. in two barrels cut. Core hardness varied from Rockwell C 22 to 34 in one specimen. Magnetic inspection of all

Plating is used quite extensively. Cadmium plating appears on the supercharger oil seal rings and most of the propeller shaft in addition to

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molybdenum, and tungsten.

The one magnesium alloy found varies somewhat from American standard alloys in that it contains 4.6 percent aluminum, 2.6 percent zinc, and 0.28 percent manganese in addition to magnesium. It will be noted that this alloy is similar to AMS 4424 except that the aluminum content is low.

steel parts illustrated acceptable material.

showed

In the aluminum alloys found, 17S is used for many parts such as main crankcase, tappet guides, piston-pin plugs, and so on. For special purposes such as pistons, cylinder heads, and supercharger front housing, an alloy containing 3.93 percent copper, 1.37 percent magnesium, and 1.67 percent nickel is used either cast or forged.

An all-purpose steel, either case- hardened or hardened throughout, is used for connecting rods, crankshaft, valve rockers, and so on. Fig. 5 shows a section of crankpin. It contains approximately 1.5 percent chromium, 3.5 to 4.5 percent nickel, 0.3 to 0.4 percent molybdenum, 0.35 to 0.5 percent manganese, and varying small quantities of silicon and copper apparently as impurities. Carbon content is varied as required. The same steel with the molybdenum reduced and 0.5 to 0.9 percent tungsten and 0.2 to 0.4 percent cobalt added is used in the propeller

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