Gas distribution mechanism. Why is it needed?

Gas distribution mechanism - one of the most important parts of the engine, the correct operation of which directly affects its performance. It serves for the timely filling of cylinders with a combustible mixture or air (in injector and diesel engines), as well as for the release of exhaust gases. The timing system includes a camshaft drive, it can be belt, chain, or by means of gears, the camshaft itself and the valve mechanism. The last major parts are the valves and rocker arms. The latter, in turn, are fixed on the axis in such a way that one of its levers rest on the adjusting screw, and the second - on the valve stem.

The camshaft is an axis on which eccentrics (cams) are pierced, in accordance with the angles of the valve timing. The valve timing is the time when the valve opens and closes. This occurs at the time when the cylinder is at the top or bottom dead center. Which valve opens, (inlet or outlet) depends on what bar is in the cylinder.

For example, if the piston is at the bottom dead center and the compression stroke begins, then all the valves are closed, if this is the exhaust stroke, then the exhaust valve is open. It is logical to assume that in the stroke stroke all the valves are also closed, and when the intake is open, the intake valve is open. The gas distribution mechanism can have one camshaft or two. The OHC gas distribution mechanism is the first case, the second one was called the DOHC. This arrangement is used only in those engines in which each cylinder has 4 or more valves, such as 5 for Audi.

Therefore, the gas distribution mechanism DOHC allows you to achieve greater engine performance, and also make it more environmentally friendly and economical. Each camshaft is designed to open one group of valves: either intake or exhaust.

It was preceded by the gas distribution mechanism SOHC. It also has 4 valves per cylinder, but only one camshaft is used to open them. Such a timing was widespread in the 1990s, but was soon abandoned because of its low productivity compared to DOHC.

Assemblage means correct installation of a camshaft in relation to a cranked shaft. It is achieved thanks to the marks on the gear which need to be combined. When using a belt drive , pulleys are first installed, marks are combined, after which they are fixed and the timing belt is fastened, which is then tensioned by a tension roller.

The gas distribution mechanism does not require almost any maintenance, it boils down to the timely adjustment of the gaps in the valve drive. Its violation leads to increased wear of parts, and also does not allow the engine to develop its full power. In addition, this can lead to the hanging of the valves, they will be constantly in a slightly open position, and damage to the pistons, and replacing even one can be quite expensive.