A cam is a rotating member which imparts reciprocating motion to another member called the follower in a plane which is at right angles to the cam – axis.
Its profile is shaped such that a smooth rise and fall for the predicted motion of the follower is provided which is transmitted to the individual values.
It is mounted on a cam – shaft lifts the tappet during its rotation. The tappet actuates the push rod and the push rod. It operates the rocket arm about its fulcrum. A pressure is exerted on the valve stem by the rocker arm against the spring to move it in the guide. This opens the valve and the fuel – air mixture enters into the cylinder. When the camshaft rotates further, the non – eccentric portion of the cam comes in contact with the tappet. The valve gets pushed back on its seat by the valve spring, thus closing the valve.
We also have tappet clearance which is the clearance between the cam and the tapper so as to allow for the expansion due to heat. The valves should close and open properly and the gas tightness is to be maintained. In order to meet this purpose, tappet clearance is allowed. This valve strain clearance is called valve lash. It should not be excessive, else, it will cause noise or permanent failure. The Combustion chamber and intake runner shapes can multiply the advantages of an increase in cam – shaft profile. Stock cams are also known as the original equipment cams. They typically has a cam fixed for higher efficiency .But it has a lower RPM (rotations per minute ) rotations per minute that most vehicles drive at. As these cams get fixed for low RPMs, they may leave the performance gain potential for the high RPM ( rotations per minute )range.
Types of engine valves can be found here.