The news that in one of his new bikes (the future Multistrada V4) Ducati switched to traditional distribution, with valves recalled by springs, after having linked its name exclusively to desmo engines for about thirty years, it raised a fuss.
Fans of the Bolognese house, and beyond, have been divided between those who criticize and those who approve of the decision. Which for the moment concerns only a model intended for a granturistic use or in any case not sporting (the engine is called not by chance V4 Granturismo). Certainly, before taking it the direction of the company will have thought about it.
In this regard, the great perplexity expressed by many enthusiasts comes to mind when the Porsche, for its six-cylinder flat engines, has abandoned air cooling and switched to the water one. This made it possible to fall within the increasingly severe limits in terms of emissions and made it possible to use heads with four valves per cylinder, located on two planes very little inclined to each other, with considerable advantages in terms of performance.
Later the German company even inaugurated a completely new “trend” with the Cayenne, powered by an a eight-cylinder V placed at the front.
The impression is that Ducati is doing something like this, opening a new line. However, desmo enthusiasts should not worry; distribution of this type it will continue to be used on sportier models for its refinement and uniqueness. After all, beyond all technical and marketing considerations, it is very difficult to think that the extraordinary know-how accumulated in such a particular sector could one day be lost …
The origin of the Desmo
Desmodromic distributions were born to overcome the strong limitations caused by springs recall of the valves, long authentic Achilles heel of racing engines.
Reliability left much to be desired to begin with and for decades breaks of these components have been far from rare. Added to this was the fact that it was precisely the springs a prevent the achievement of schemes of rotation higher, as the technique progressed and the attempt was made to obtain progressively higher performances. The modest characteristics and the poor quality of these mechanical organs limited the accelerations of the valves that it was possible to adopt.
To be able to reach adequate lifts the technicians were forced to use extremely long valve timing, in order to raise the valves with considerable gradualness. This however involved a strong reduction of the field of use, for which “tight” valve timing is advantageous.
Large valves (two per cylinder at the time) and springs with a high load were used but generally the lifts were relatively modest, in relation to the diameter of the mushrooms.
Proposals e patents related to desmodromic distributions have succeeded starting from the pioneering period of motorsport.
The Delage he used a bracket system on a couple of occasions in 1914, but this was not followed up.
The first house to really believe in the desmodromic and to use it with great success was there Mercedes Benz which first patented and then used a distribution of this type in its cars that have conquered the world title in 1954 and in 1955.
L’ing. Scheremberg pointed out the advantages they had gained over their racing engines in a technical article that appeared in ATZ in 1955.
Compared to a conventional type distribution (with valve return springs) it was possible to increase the lift by 42% and reduce the duration of the suction phase from 284 ° to 256 ° (while obtaining a significantly greater angle-area). At the same time, the maximum negative valve acceleration had more than doubled!
Given the extraordinary successes of the Mercedes-Benz Formula One, several other manufacturers soon turned their attention to desmodromic distributions. It is enough to recall in this regard the proposals of the Norton and of Global, remained at the prototype stage), and that of the MV Agusta (whose 125 desmo ran a couple of times).
In the auto field only the OSCA for some time he used a desmodromic distribution on his sports cars. There Scarab he did it for two or three races in 1960.
The engine Porsche eight-cylinder Formula One appeared in 1962 it was also tested with a desmodromic distribution (never used in the race) which, compared to the traditional solution, allowed the positive acceleration of the valves to be increased by 32% and to double the negative one. The F1 commitment of the manufacturer from Zuffenhausen ended shortly after.
On the first Ducati in 1956
The first Ducati with desmodromic distribution appeared in 1956. It was the 125 from the Grand Prix, in which a third centrally located camshaft was added to the two camshafts of the usual double-shaft layout, which calls up the valves by means of two-arm rockers arranged in an upside-down position with respect to the usual one.
For the series production later the engineer. Taglioni studied a scheme with a single camshaft which provided both to open and to recall the valves. Distribution of this type has begun to be adopted on the single-cylinder series “with wide casings“Of 250 and 350 cm3 in the autumn of 1968 (the 450 arrived a few months later).
Later the models with two L-shaped cylinders, equipped first with the spring distribution and later also with the desmodromic one (starting with the sportier versions). Gradually the models with conventional distribution have therefore given way to desmodromic ones.
Some time later the models with water cooling and four valve heads, which have been equipped with a new desmodromic distribution bialbero, still in use.
In this case, the diagram provides that each shaft is equipped with an opening cam (which acts on a finger rocker) and a closing one for each valve. The same solution was then adopted on the four-cylinder models, both racing and series.
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