The camshaft, on most modern engines, is mounted in bearings formed into the cylinder head via an in-line boring process . The camshaft is forged from steel or cast iron and the bearings and cam surfaces are a smooth, machined finish. The camshaft has cam lobes for each valve and to ensure the correct sequence of valve timing, the camshaft is timed and synchronized with the crankshaft position.
The cam lobes have a specific profile that consists of a base circle and lobe to provide the correct valve opening and closing characteristics . The cam profile is not necessarily symmetrical and the profile may allow progressive opening of the valve but with a sharp closing action depending on the characteristics and optimization parameters of the engine.
Overhead valve (OHV) is used to describe an engine where the valves and operating mechanism are located in the cylinder head. The valve gear transfers reciprocating motion from the cam followers and camshaft. It is then passed to the valves via push rods and a rocker assembly, which acts on the valve stems .
Overhead cam (OHC) refers to the position of the camshaft in the engine; that is, it is positioned in the cylinder head. There are various designs using direct or indirect mechanisms to convert the rotating cam motion into a reciprocating motion, and then transfer this motion to the valve stems. These designs are proposed to facilitate a close tolerance in operating clearances.
A further development, now employed extensively, is the use of twin or double overhead camshafts (DOHC) . These can use direct or indirect valve