The motor shown at [Fig. 92], B and [Fig. 88] employs cylinders of the “L” type. Both valves are placed in a common extension from the combustion chamber, and being located side by side both are actuated from a common cam-shaft. The inlet and exhaust pipes may be placed on the same side of the engine and a very compact assemblage is obtained, though this is optional if passages are cored in the cylinder pairs to lead the gases to opposite sides. The valves may be easily removed if desired, and the construction is fairly good from the viewpoint of both foundry man and machinist. The chief disadvantage is the limited area of the valves and the loss of heat efficiency due to the pocket. This form of combustion chamber, however, is more efficient than the “T” head construction, though with the latter the use of larger valves probably compensates for the greater heat loss. It has been stated as an advantage of this construction that both manifolds can be placed at the same side of the engine and a compact assembly secured. On the other hand, the disadvantage may be cited that in order to put both pipes on the same side they must be of smaller size than can be used when the valves are oppositely placed. The “L” form cylinder is sometimes made more efficient if but one valve is placed in the pocket while the other is placed over it. This construction is well shown at [Fig. 92], D and is found on Anzani motors.
Fig. 93.—Sectional View of Engine Cylinder Showing Valve and Cage Installation.
The method of valve application shown at [Fig. 87] is an ingenious method of overcoming some of the disadvantages inherent with valve-in-the-head motors. In the first place it is possible to water-jacket the valves thoroughly, which is difficult to accomplish when they are mounted in cages. The water circulates directly around the walls of the valve chambers, which is superior to a construction where separate cages are used, as there are two thicknesses of metal with the latter, that of the valve-cage proper and the wall of the cylinder. The cooling medium is in contact only with the outer wall, and as there is always a loss of heat conductivity at a joint it is practically impossible to keep the exhaust valves and their seats at a uniform temperature. The valves may be of larger size without the use of pockets when seating directly in the head. In fact, they could be equal in diameter to almost half the bore of the cylinder, which provides an ideal condition of charge placement and exhaust. When valve grinding is necessary the entire head is easily removed by taking off six nuts and loosening inlet manifold connections, which operation would be necessary even if cages were employed, as in the engine shown at [Fig. 93].
Fig. 94.—Diagrams Showing How Gas Enters Cylinder Through Overhead Valves and Other Types. A—Tee Head Cylinder. B—L Head Cylinder. C—Overhead Valve.
