Over Head Valve Mechanism.

Don't Click Here: The over head valve mechanism is explained in this topic. It is the most widely used valve arrangement mechanism.

--Technical Videos--

The main components of this mechanism as shown in fig1:

1. Cam.
2. Valve lifter.
3. Push rod.
4. Rocker arm.
5. Spring.
6. Valve guide. 

Working of over head valve mechanism:Don't Click Here:

Fig: 1, Over head valve mechanism.

Stage 1 (Valve opening): As show in the fig:1, the cam (the profile of cam is oval in shape) rotation lifts the valve lifter due to its profile, the valve lifter is connected to the push rod and intern connected to the rocker arm. So the movement of the valve lifter is reflected through the push rod towards the rocker arm. Due to this arrangement, as the push rod hits the rocker arm, it will tend the rocker arm to move done. As rocker arm moves down, it will hit the valve and will move the valve down (valve opens to the cylinder) resulting the air fuel mixture to enter the cylinder.  

Stage 2 (Valve closing): As the cam rotates again its profile changes and the load exerted by the cam on the valve lifter reduces, as the spring on the valve shown in fig:1 is in compression (due to the valve opening) retains its position and closes the valve.--Technical Videos--