The camshaft should open the valves at the right time, lifting them an exact amount and in a precisely determined sequence and make it possible for them to be closed again through the valve spring. The modern camshaft is driven by the crankshaft through gearwheels, timing belt or timing chain. In all cases, there is a transmission ratio of 2 : 1. Thus, the camshaft rotates only half as fast as the crankshaft.
Engine control: through shape and adjustment of the cams
A distinction is made between overhead- and side valves. In the case of the OVH-control, the camshaft is installed in the bottom of the engine block. The valves however, do their job in the cylinder head and are thus called overhead valves. The camshaft causes the valves to move through pushrods and cam followers. Because when the valves close and more components have to be moved back by the valve spring, higher RPM is not possible, side-valve engines are nowadays, only found the large volume (USA) V8-motor car-engines and in truck-engines. One, or two lie horizontally in the cylinder head and are driven through rocker-arms, cam followers or directly through tappets. The timing can, through either a mechanical- or a hydraulic adjustment be changed according to the engine speed.
The camshafts are made from cast iron, nodular cast iron, tempered steel or nitrided steel. They can be either cast or hollow-bored to save weight. Their bearings and the cam-paths are mostly surface-hardened. Camshafts can also be assembled from individual parts. Thereby, the cams and the bearings are pressed into their exact position through very high (water) pressure and then fixed. In contrast to the one-piece components, the cams can then be made from sintered material. The advantages are, lower production costs and weight-saving. 01/12