Fig. 189.—Methods of Testing to Insure Parallelism of Bearings After Fitting.
When the connecting rods are being fitted with the crank-shaft in place in crank-case, and that member secured in the frame, a steel square may be used as it is reasonable to assume that the wrist-pin, and consequently the piston it carries, should observe a true relation with the top of the engine base. If the piston side is at right angles with the top of the engine base it is reasonable to assume that the wrist-pin and crank-pin are parallel. If the piston is canted to one side or the other, it will indicate that the brasses have been scraped tapering, which would mean considerable heating and undue friction if the piston is installed in the cylinder on account of the pressure against one portion of the cylinder wall. If the degree of canting is not too great, the connecting rods may be sprung very slightly to straighten up the piston, but this is a makeshift that is not advised. The height gauge method shown above may be used instead of the steel square, if desired, because the top of the crank-case is planed or milled true and should be parallel with the center line of the crank-shaft.
CAM-SHAFTS AND TIMING GEARS
Knocking sounds are also evident if the cam-shaft is loose in its bearings, and also if the cams or timing gears are loose on the shaft. The cam-shaft is usually supported by solid bearings of the removable bushing type, having no compensation for depreciation. If these bearings wear the only remedy is replacement with new ones. In the older makes of cars it was general practice to machine the cams separately and to secure these to the cam-shaft by means of taper pins or keys. These members sometimes loosened and caused noise. In the event of the cams being loose, care should be taken to use new keys or taper pins, as the case may be. If the fastening used was a pin, the hole through the cam-shaft will invariably be slightly oval from wear. In order to insure a tight job, the holes in cam and shaft must be reamed with the next larger size of standard taper reamer and a larger pin driven in. Another point to watch is the method of retaining the cam-shaft gear in place. On some engines the gear is fastened to a flange on the cam-shaft by retaining screws. These are not apt to become loose, but where reliance is placed on a key the cam-shaft gear may often be loose on its supporting member. The only remedy is to enlarge the key slot in both gear and shaft and to fit a larger retaining key.
CHAPTER XII
[Aviation Engine Types]—[Division in Classes]—[Anzani Engines]—[Canton and Unné Engine]—[Construction of Gnome Engines]—[“Monosoupape” Gnome]—[German “Gnome” Type]—[Le Rhone Engine]—[Renault Air-Cooled Engine]—[Simplex Model “A” Hispano-Suiza]—[Curtiss Aviation Motors]—[Thomas-Morse Model 88 Engine]—[Duesenberg Engine]—[Aeromarine Six-Cylinder]—[Wisconsin Aviation Engines]—[Hall-Scott Engines]—[Mercedes Motor]—[Benz Motor]—[Austro-Daimler]—[Sunbeam-Coatalen].