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Aviation History
1924
1924 - 0497.PDF
AUGUST 7, 1924 two cams operate one exhaust valve each. The principle and most of the details should be clear from the accompanying analytical sketches. The casings containing the rockers, tappets, &c, are carried on two long bolts rising from the cylinder heads, the overhead camshafts passing between these bolts. The camshafts, incidentally, are enclosed in tubular steel casings carried between the valve cages and the rocker covers, and each camshaft runs in six aluminium bearings. These are of the split type, while the end bearings are of the gudgeon pin and one at the base of the skirt. The upper and lower are scraper rings, while the middle are compression rings. The connecting rod assembly is shown in some of our illustrations. It will be seen that here again there is a marked difference between the " Eagle " and the " Condor." In the former, it will be recollected, articulated rods are employed, while in the " Condor " the rods are forked, not only over the crank pins but also one of each pair over its 4F' v ?*<# ' • ' k • , i 41 UP4 if 11 , m-mm^t ' T- W- «P W * •' *C Ft r One of the overhead camshafts of the " Condor." Shafts and valve mechanism are supported by long studs from the cylinder heads. one-piece type. The camshafts themselves are of 5 per cent, case-hardening nickel-steel bar, ground true on the bearing surfaces and cam faces. As already stated, the camshaft drive is in the form of inclined tubular shafts with bevel gears at upper and lower ends, driven from the rear end of the crankshaft. Out-of- alignment and expansion effects are allowed for by hardened serrated couplings, and the inclined driving shafts are sup ported in ball bearings. The gears for driving the camshafts and all auxiliaries are driven from the rear end of the crank- mate. The rods are of " H " section, and are made from 3£ per cent, nickel steel forgings, heat treated to give a high Brinell number, and machined all over to reduce weight variations. A divided white-metal lined steel block is bolted to the forked rod, and the plain rod works on the centre portion of the steel block, the latter having a white-metal bearing surface. The small ends of both rods are fitted with floating phosphor bronze bushes. All bearings are positively lubri cated under pressure, and in the case of the connecting rod ends it will be seen that the oil is carried bv a small tube Analytical sketch of the rocker mechanism, tappets, etc. Inset, a suggested mounting arrangement allowing for longitudinal expansion. shaft through the medium of a spring-controlled friction- damped pinion.which eliminates crankshaft torsional vibration from all auxiliary drives. The pistons are made of a special aluminium alloy, and are of the " Zephyr " type, for which it is claimed that the crown is better supported while the cooling of the head is considerably improved. There are four piston rings, three above the which is given a series of zig-zag bends in order to relieve the stresses in it. The six-throw crankshaft is machined from a nickel chrome steel forging, and all journals and crankpins are bored for lightness and to convey oil to all bearings. Crankpins and journals are ground to close limits for size, and the shaft is carried in seven plain bearings of generous proportions. The 497
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