The driving with valves at the head are an alternative to the driving with side valves. One can meet them on all kinds of four-stroke engine architectures of (out of V, line, etc)

In the overhead valve engines one can distinguish the side camshaft engines and the single camshaft engines at the head (collapsed).

The provision at the head, i.e. above the Cylinder, makes it possible to have a better circulation of gases and better a Ratio compression than the side valve engines.

On the other hand, it exposes to the Affolement of valves (impossibility for the valve of returning in time on its seat to the high modes), being likely to cause the breaking of the engine because the head of valve moves in the zone swept by the piston.

This disadvantage, raised on the collapsed engines, is suppressed by the engines with distribution Desmodromique.

In Automobile industry , the collapsed engines with valves at the head and side camshaft were the standard until the arrival of the engines with Camshaft at the head.

Advantages and disadvantages of the valve engines at the head.

The valve engines at the head and side camshaft are exposed to the panic of the valves. The joined together mass of the valves, the pushrods, and the tumblers causes a too important inertia with high mode.

The fuel rating of the engines to valves at the head and side camshaft is often lower than that of the engines with Camshaft at the head. This is related to the provision in lines of the valves in the combustion chamber what harms the filling (engines of Renault 4 for example).

The valve engines at the head have a curve of power and linear couple. The engine torque available to low mode makes it possible to use transmissions having less reports/ratios.

The simple and more compact design of the valve engines at the head collapsed than that of the camshaft engines at the head makes it possible to lower the center of gravity of the cars and the production costs of the engines.

The systems making it possible to decontaminate a line of cylinders are easier to install on a valve engine at the head, which makes it possible to reduce fuel consumption when the engine is requested little.