LO 9-2 Describe the functions, construction, composition, types, and applications of diesel engine cylinder head assemblies

LO 9-02: Describe the functions, construction, composition, types, and applications of diesel engine cylinder head assemblies.

Classification by Valve Train Arrangement

Cylinder heads are further classified by the arrangement of the valve train mechanism. For example, the camshafts in diesel engines are commonly one of two types—either an overhead camshaft or in-block camshaft Figure 18. Overhead camshaft engines have one or two camshafts located in the cylinder head. The most important reason for the use of overhead camshafts in early engines, built in the late 1980s, was to eliminate injector pushrods. Pushrods can bend during high- pressure injection events. These overhead camshaft engines use unit injectors, which are often actuated directly by a camshaft that enables the highest injection pressures. Without the natural bending and flexing of pushrods, overhead camshafts increase the maximum pressure of the injection event. Valve timing is also more accurate and easier to vary in an overhead camshaft configuration Figure 19. In-block camshafts have only the valves, rocker levers, and bridges located in the cylinder heads above the piston, and the camshaft is located in the engine block Figure 20. This camshaft arrangement is also simply referred to as a pushrod engine because the camshaft actuates the valves through a pushrod and rocker lever Figure 21.

FIGURE 09-18: A low-mounted camshaft in this block is supported by camshaft bushings.

FIGURE 09-19: This engine uses a single overhead camshaft and unit injectors.

FIGURE 09-20: This small two-valve/cylinder industrial diesel engine uses pushrods and an in-block camshaft.

FIGURE 09-21: Compare A. an overhead camshaft design with B. the in-block camshaft valve configuration.

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