Unformatted text preview: on ‘Theory of Machines’. 1190 n A Textbook of Machine Design The fuel is admitted to the engine by the inlet valve and the burnt gases are escaped through the
exhaust valve. In vertical engines, the cam moving on the rotating camshaft pushes the cam follower
and push rod upwards, thereby transmitting the cam action to rocker arm. The camshaft is rotated by
the toothed belt from the crankshaft. The rocker arm is pivoted at its centre by a fulcrum pin. When
one end of the rocker arm is pushed up by the push rod, the other end moves downward. This pushes
down the valve stem causing the valve to move down, thereby opening the port. When the cam
follower moves over the circular portion of cam, the pushing action of the rocker arm on the valve is
released and the valve returns to its seat and closes it by the action of the valve spring.
In some of the modern engines, the camshaft is located at cylinder head level. In such cases, the
push rod is eliminated and the roller type cam follower is made part of the rocker arm. Such an
arrangement for the horizontal engines is shown in Fig. 32.20 (b...
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- Spring '11