Valve Control (desmodromic)

Function

The desmodromic valve control closes the valve without the help of a valve spring. Fluttering of the valves at very high revs is thereby avoided. Moreover, the acceleration and deceleration during the valve control are improved. The real reason for the implementation of this valve control system lies in the bad quality of the steel after the Second World War which caused the valve springs to break over and over again (in particular for racing engines).

How it works

Instead of one cam, the camshaft features one cam for opening (blue) and another for closing (red) the valve. The valve is directly attached to the rocker arm. An exact valve adjustment is especially essential, yet complicated. For example, the sleeves on the valve stem must be renewed or grinded off if the valve clearance is altered.

Application

Motorcycles feature this valve control sporadically (Ducati). Even for racing engine cylinder heads with valves, very high revs are realised exclusively with valve helical springs and/or air-filled diaphragms. 06/08