alloy plugs pressed into the pin. The heads of these plugs are relatively thick and the spherical contacting area is decreased by a large chamfer. Two angular holes through this chamfer serve the dual purpose of
venting the cooling means.
VALVE GEAR — The cam is a
in turn, is
a push fit
track ring running on a tin- cast bushing of very good
cam is case-
hardened to Rockwell C 60. Core hardness is Rockwell C 32. The drive is through a pair of spur gears from the crankshaft to the intermediate cam drive. This intermediate cam drive is mounted on a stub shaft on the crankshaft front main diaphragm and is made as a cluster gear incorporating a pinion which drives the internal gear integral with the cam. A bronze bushing in the cluster gear completes the assembly. It is interesting to note that no lock is provided on the screw which retains this gear, rotation being such that the right-hand thread is expected to tighten during engine operation. This gear train provides for cam rotation at on-sixth crankshaft speed and in a direction opposite the crankshaft rotation. Three lobes on each cam track provide for operation of all fourteen exhaust and all fourteen intake valves. As was noted previously, cam lobes and tappets are tilted at an angle of 14 deg.-30 min. to provide more nearly straight-line action of the push rods and tappets. Thrust resulting from this angle is taken through th flange of the cam bearing ring to the intermediate front section diaphragm. As a result, the designers have found it permissible to retain the cam by three short retaining pieces each held by two studs which also pass through holes in a second flange on the cam bearing ring. Clearance for the internal cam gear is provided underneath the retainers. The cam is designed with constant- velocity pick-up and seating sectors for a running clearance of 0.045 in. ± 0.025. At 2,000 rpm., pick-up and seating velocity of both intake and exhaust valves is 1.95 fps. The cam design gives 50-deg. overlap, 264
approximately as follows, although an accurate check was not made: inlet opens 20 deg. early, closes 64 deg. late; exhaust opens 80 deg. early, closes 30 deg. late. Valve lift is 0.54 in.
Tappets are arranged in pairs in 14 17S aluminum-alloy tappet guides (one per cylinder). A great deal of machining was done to cut these guides out of what must have been extremely simple forgings. They are bored and slotted elaborately for various reasons including oil feed and drainage. Tappets are Rockwell C 61 throughout, although the photomicrographs show a change in structure near the surface. They are 0.62-in. diameter and are fitted with pressed-in ball sockets for push-rod actuation. Tappet rollers, 1.25-in. diameter (Fig. 22), are Rockwell C 61 throughout and are mounted on 0.31 in. diameter case-hardened (Rockwell C 61 case, 30 core) floating pins. Push rods are low chrome-alloy steel tubing with pressed-in ball ends of low-alloy steel heat-treated to a hardness of Rockwell C 30, except at the tip which is quenched to obtain a hardness of Rockwell C 60. Fig. 23 shows a section of the push-rod ball end. Push-rod housings are aluminum alloy attached by means of a packing gland type joint to the cylinder rocker box. There were no lower push-rod housing connections available when the engine was inspected, but photographs of a similar engine indicate a single piece which forms attachment for two push-rod housings and is, in turn, attached to the crankcase by the three studs which also retain the tappet guide block.
Valve rockers are cadmium-plated steel forgings of the alloy described previously. See Fig. 24.) They oscillate on pressure-lubricated plain tin-bronze bushings pressed and pinned into a bore in the arm. These ride on a flanged steel journal supported by a stepped rocker bearing bolt. Rocker thrust is taken by the bushing flange against a shoulder on the journal. The push- rod ball socket is permanently installed in one end of the rocker. Adjustment is at the valve end by means of a screw threaded into the arm and locked by means of a jam nut. A flatted ball bears on the valve stem and is seated in the adjusting
screw, providing a familiar type of construction.
Hollow-head and -stem exhaust valves (Fig. 25) and the familiar “tulip” head solid-stem intake valves (Fig. 26) are used. The exhaust valve steel is the high-chromium, high- nickel plus tungsten and cobalt alloy generally used in this application. It is forged and machined in one piece with welded Stellite tip and face. Face and tip hardness is Rockwell C 56; stem Rockwell B 96. and head, Rockwell B 93. Metallic sodium is used as a coolant. The inlet valve is a familiar material with 13.2 percent tungsten, 3.2 percent chromium, 0.8 percent nickel, 0.1 percent cobalt, 0.4 percent manganese, 0.4 silicon, and 0.5 percent carbon. Rockwell C 35 to 45 with the tip hardened to 55.
Major valve dimensions are as follows: exhaust, 2.53-in. diameter head, 45-deg. face, 0.62-in. diameter stem; intake, 2.67-in. diameter head, 45-deg. face, 0.46-in. diameter stem. Valves seat on inserts in the cylinder head as mentioned previously. The bronze intake insert is 2.75-in. OD by 2.24-in. ID; the steel exhaust insert is 2.67-in. OD by 2.18-in. ID. Valve-spring upper washers are retained by a split lock incorporating a tapered OD and a corrugated ID which fits three circumferential semi-circular grooves in the valve stem. Two springs are used per valve
the inner seating on a washer on
the guide flange and the outer on a loose steel washer in the cylinder. Springs are cadmium-plated carbon steel with a hardness of Rockwell C 40. Quality is very good.
REDUCTION GEAR — the 0.7:1 propeller reduction gear is of the planetary type; parts are shown in Fig. 27. A large internal gear with 84 teeth is splined to the crankshaft front extension as described previously. This gear is of two-piece construction, being made up of a flange integral with the splined hub. The internal ring gear is attached to the OD of this flange by means of a large number of small diameter trough bolts. The roots and flanks are Rockwell C 62. Core hardness (including tips) is C 26. The 36-tooth sun gear of this planet set is attached to the crankcase front section by through bolts in the conventional manner. Roots and flanks of this gear are Rockwell C 60. Core hardness (including tips) is C 38. (See Fig.