Technique! Everything about desmodromische klepbediening

Posted on 29-04-2016 at 21:12 by MauritsH – 37 Comments”

You had to be a tech special?

Nice, we will arrange that on the Friday night. In the year 2016 think of the lover, upon hearing just the word “desmo” to only one brand: Ducati. Indeed, who do not build cars. Fortunately, this wonderful technique is also enough in common with the car industry to be on AB is a small article to devote to it.

The disadvantages of valve springs and camshafts

Timing is particularly crucial for the “character” and the life of the engine. Hot(re) camshafts, VTEC, variable valve timing in all its variants and characteristics: it is commonplace and virtually all of these systems are based on (or parent) of the camshaft and associated valve springs. The basic principle is quite simple. The camshaft pushes the valve down, causing the mixture in the combustion chamber in or out, the spring pushes the valve back in place and close the combustion chamber again. A concise explanation you can read HERE.

A big risk with the conventional setup, is the risk of floating valves. That works roughly as follows. Certainly in racing is life often subordinated to power. Ergo: the maximum speed is jacked up so extra hp’s from that block to the door. This involves the risk that the valves may not be quick enough to close, leaving the still unburnt mixture already in the combustion chamber can leave the spark plug still has spark. Not cool, because loss of power.

With a little luck leads the above to one or more burnt valves, with a lot of bad luck ramming the door right through you piston back and you can make a side table from the engine. And we’re not even talking about the risk of sneuvelende springs, with all the consequences. The most obvious solution to this problem is the mounting of tougher springs, but then the engine work harder to turn the valves to push down. Fortunately, it can also be different!

Desmodromisch = forced klepbediening, even up

For the record: desmo’s were and are in many different forms built, so it is not one particular system. However, all these systems have certain things in common with each other, which we now try to explain.

Probably was desmodromische klepbediening invented in 1896 by Gustav Mees. This system was not only downward, but also upward movement of the valve of choice is forced to take place. The big advantage is if the well is immediately apparent. In this way can (at any speed!) after all, much more accurately determine how long the valve is open, which is beneficial for both the ability as well as for the life span. The above-mentioned risks do not, in fact, more or less at the smo’s. In addition, the system is a lot more consistent, because the valve always with the same power up and down is driven. There, you’ll get a whole nine yards to disadvantages for the back, where we will pay attention to.

The operation of (a form of) the system, check below. This variant of Ducati has feitenlijk two cams per valve. One ridge point to the downward movement of the valve, the other “pulls” the valve as the true back up. Clever!

Fortunately, there are also plenty of cars built that were fitted with this beautiful technique. In addition to the Mercedes W196 F1 car you see above had to be at least as famous 300 SLR also a motor with desmodromische technique. That is still the most important, or most famous, the cars that are relevant in this context.

The disadvantages

Of course, know this technique also its downsides. The most important is also the most obvious. More technology also means that the quantity complex. In this case, because the valve train is in this respect above the combustion chamber and the hot. Materials can also (temporarily) distort as soon as the mercury is rising and that is not cool at adjusting technique that, in and of itself is complicated enough.

Then we arrive at the following tip. Complex technology that higher speeds are possible, it can only mean one thing: more maintenance. Friends or acquaintances with a Ducati can undoubtedly all about it tell, all we have to say that the Italians today, it is a lot better for each other to have some reliability concerns. That was formerly sometimes otherwise.

The last point is somewhat debatable, but definitely worth a mention. New techniques and materials ensure that engines with a more regular valve train to withstand higher rotational speeds, without the service life is thereby severely compromised. You might wonder how relevant desmodromische klepbediening still is. Indeed, this question is actually already answered by the fact that virtually no single engine or car manufacturer still in a serious scale. Apart from Ducati, indeed.

Toegiftje

Still a modest allowance. Because, as colleague @Dizono recently explaining, with a beautiful motorcycle nothing is wrong. And because the beautiful technique remains, of course.

Photo via this forum