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the cylinders have been removed is clearly indicated at Fig. 92. In this case the magneto or water pump has not been disturbed. The pistons, piston rings, and connecting rods are clearly exposed and their condition may be readily noticed.
Before disturbing the arrangement of the timing gears, it is important that these be marked so that they will be replaced in exactly the same relation as intended by the engine designer. If the gears are properly marked the valve timing and magneto setting will be undisturbed when the parts are replaced after overhauling. When an engine has been taken down to the point shown at Fig. 92, it is possible to ascertain if there is any undue wear present in the connecting rod bearings at either the wrist pin or erank pin ends and also to form some idea of the amount of carbon deposits on the piston top and back of the piston rings. Any wear of the timing gears can also be determined. The removal of the bottom plate of the engine enables the repairman to see if the main bearings are worn unduly. Often bearings may be taken up sufficiently to eliminate all looseness. In other cases they may be worn enough so that careful refitting will be necessary.
All engines are not of the type shown at Figs. 88 and 89. Where the crankcase is divided horizontally into two portions, the upper one serving as an engine base to which the cylinders and in fact all important working parts are attached, the lower portion, performs the functions of an oil container and cover for the internal mechanism. There is a tendency on the part of modern designers to combine the cylinders and a portion of the crankcase in one casting, using a detachable cylinder head construction in order to permit valve grinding and carbon removal without taking the engine out of the chassis frame. The connecting rods and pistons may also be removed where this construction is followed through the opening left after the detachable cylinder head is removed. In the engine shown at Fig. 93, not only the cylinders but practically the entire engine crankcase, except for the plate closing the bottom is cast in one unit. It will be evident that the removal of the bottom plate and cylinder head will provide access to the interior of the motor. Attention is directed to the inlet manifold construction which is cored in the cylinder block. The exhaust
manifold however, is a separate casting secured to the cylinder block in the usual way.
The important parts of an engine of the conventional four cylinder pattern where the cylinders are cast in pairs are clearly shown at Fig. 94, and their appearance may be readily noted. It will be evident that when the bottom of the crankcase is removed the crankshaft is exposed and the main bearing caps may be released by unscrewing the bearing cap retention bolts. A number of parts of typical engines are also indicated at Fig. 95. The view at A, shows the appearance of the usual arrangement of the
Fig. 92.—View of Automobile Engine with Cylinders Removed to Expose
Pistons and Connecting Rod and with Timing Gear Case Taken Off to Expose Gearing.
timing gears when cylinders of the T-head form are employed. As will be apparent one large gear is carried by each camshaft, these being turned by a pinion of half their size on the crankshaft. The method of retaining the timing gear varies with the construction of the engine. In the form shown at A, the gears are held on the flanged camshaft end by three square head cap screws which are wired together to prevent loosening. In the construction shown at Fig. 92, the camshaft gears are securely held by four