Valve Train (Camshaft, Rocker arm, Pushrods) By: Hewett Sze Objective: To give an overview of how these components function in an engine and how their configurations affect engine performance.

Valve Train The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a camshaft.

Camshaft http://static.howstuffworks.com/gif/camshaft-ch.jpg http://www.familycar.com/classroom/Images/Engine_Camshaft.gif

Cams continued… The camshaft uses lobes (called cams) that push against the valves to open them as the camshaft rotates Springs on the valves return them to their closed position

http://auto.howstuffworks.com/engine-cam2.htm

A pictorial representation of intake and exhaust valves http://www2.gsu.edu/~bioasx/engine.gif

Rocker Arm Works as an intermediary between the camshaft and the valves Camshaft cam pushes up on the rocker arm (via a push rods) which in turn pushes down on the valves

Piston Engines Some older engine models placed the camshaft below the pistons Pushrods actuated rocker arms above the cylinder head to actuate the valves. Lifters or tappets reside in the engine block between the camshaft and pushrods.

Overhead Cam Systems Place the camshaft above the cylinder heads and drive the valves or lifters directly instead of using pushrods. This arrangement is more complex, and relies on a timing belt or chain, but allows for greater valvetrain flexibility.

Single Overhead Cam (SOHC) One Camshaft is located above the valves The one camshaft controls both the inlet and exhaust valves

Dual Overhead Cam (DOHC) Two camshafts for each bank of cylinders DOHC engines have separate camshafts for inlet valves and exhaust valves DOHC allow for more valves in each cylinder than SOHC More valves allow for greater intake and exhaust flow and greater engine power

Conclusion 3 types of engines that use different valve train configurations are Piston Engines, Single Overhead Camshaft Engines, and Dual Overhead Camshaft Engines Modern Engines use overhead camshaft configurations

Sources http://www2.gsu.edu/~bioasx/engine.gif http://www.familycar.com/engine.htm http://auto.howstuffworks.com/camshaft3.htm http://en.wikipedia.org/wiki/Dual_overhead_camshaft http://www2.gsu.edu/~bioasx/engine.gif