Desmodromic mechanism is a special type of gas distribution device, which is designed to control the operation of all gas intake and exhaust valves in the ICE.

In Greek, desmodromic mechanism means controlled (controlled) movement.

The desmodromic mechanism was first introduced on Mercedes Benz cars, as well as in certain models of Fiat’s Barchetta cars in the mid-20th century. Today, this type of timing mechanism (timing gear) is installed on Ducati racing-type motorcycles.

The desmodromic type mechanism is known worldwide as Desmodromis. And not many people know about auto recycling services, and for good reason:

Construction of the Desmodromi mechanism

The Desmodromi mechanism is started by a special actuator consisting of the following parts:

A camshaft with cams (the actuator can be equipped with one or two camshafts);

Two rocker arms to open/close the valves;

Parts connecting the valves and rocker arms;






Valve sealing element.

The main purpose of the desmodromic timing mechanism of the timing system is to provide engine boost in terms of number of revolutions. This is achieved through the use of precisely aligned, special cam profiles with accelerated valve operation.

By controlling the operation of the valves in the desmodromic mechanism, an equilibrium between the value of the valve cross-section and the speed of the piston can be achieved. This equilibrium ensures efficient filling of the cylinder with fuel-air mixture (FAM).

Combustion engines that use a desmodromic mechanism operate at speeds that are often inaccessible in valve mechanisms equipped with springs. Typically, in such mechanisms, the speed of the valve springs is insufficient to retract the valves from colliding with the piston until it hits the end point.

The desmodromic mechanism is designed to prevent incomplete valve closure.

Typically, this phenomenon is caused by frequent crankshaft rotation, the inertia of the valves themselves, and the resonance of the valve springs. Such a hang-up can lead to serious damage:

Collision of valve and piston (with possible destruction or failure);

Overheating of valves;

untimely ignition of FAM, and also a further decrease in pressure of gases, decrease in working capacity of the engine and increase in quantity of exhaust gases

In case of such problems, not only the desmodromic type mechanism, but also other mechanisms can be used for their elimination:

The use of several springs, which are arranged by nesting into each other to reduce resonant vibrations;

the use of spring and valve parts made of the latest heavy-duty materials;

use of a pneumatic valve actuator, as in Formula 1

Disadvantages of the Desmodromic timing system

Despite its relevance and usefulness, such a system has a number of disadvantages that make this mechanism so rarely used:

The high cost of the mechanism itself;

Difficulty in providing maintenance. This is caused by the presence of a huge number of moving parts, which quickly wear out under heavy loads;

Complicated and cumbersome construction of the desmodromic mechanism;

High level of noise produced by high loads;

Difficulty in adjusting the thermal gaps. Adjustment in this type of mechanism is performed by means of special washers located on rocker arms. For each pair of rocker arms (upper and lower) a separate pair of adjusting washers is selected, which creates certain difficulties in the process of assembly and maintenance of the mechanism.

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