Fig. 132.—Part Sectional View of Renault Twelve-Cylinder Water-Cooled Engine, Showing Connecting Rod Construction and Other Important Internal Parts.
CAM-SHAFT AND CRANK-SHAFT DESIGN
Before going extensively into the subject of crank-shaft construction it will be well to consider cam-shaft design, which is properly a part of the valve system and which has been considered in connection with the other elements which have to do directly with cylinder construction to some extent. Cam-shafts are usually simple members carried at the base of the cylinder in the engine case of Vee type motors by suitable bearings and having the cams employed to lift the valves attached at intervals. A typical cam-shaft design is shown at [Fig. 133]. Two main methods of cam-shaft construction are followed—that in which the cams are separate members, keyed and pinned to the shaft, and the other where the cams are formed integral, the latter being the most suitable for airplane engine requirements.
Fig. 133.—Typical Cam-Shaft, with Valve Lifting Cams and Gears to Operate Auxiliary Devices Forged Integrally.
The cam-shafts shown at [Figs. 133] and [134], B, are of the latter type, as the cams are machined integrally. In this case not only the cams but also the gears used in driving the auxiliary shafts are forged integral. This is a more expensive construction, because of the high initial cost of forging dies as well as the greater expense of machining. It has the advantage over the other form in which the cams are keyed in place in that it is stronger, and as the cams are a part of the shaft they can never become loose, as might be possible where they are separately formed and assembled on a simple shaft.
