DESMODROMICS 101:

What the heck is that ?
    Well, if you have some interests in motorcycles, especially ducati's you probably would have heard about desmodromic valve systems.
    Here is quick primer on what it really means.
 

.... if i still have your attention, it's time for your introductory class in Desmodromics. First, though, a pedantic primer in how a basic four-stroke engine works, lest we in our hasty lives have forgotten...

Stroke one: A valve in the top of the cylinder opens. The piston goes down pulling in a 14:1 mixture of air and vaporized gasoline much like a medical syringe pulling in the serum when the plunger is pulled back. This is the INDUCTION STROKE

Stroke two: The valve closes and the piston moves upward. This compresses the fuel air mixture to about 1/10th it original volume. This is the COMPRESSION STROKE.

Stroke three: With all valves closed so that the piston/cylinder is sealed tight a spark ignites the fuel/air mixture and the rapidly expanding hot gases force the piston downward with great energy. This is the POWER STROKE

Stroke four: A second valve at the top of the cylinder opens and as the piston moves back up it expels the burned fuel/air mixture. (Like the syringe giving the shot) This is the EXHAUST STROKE.

Okay, simple enough, right? But what does that have to do with a weird greek-based word like "desmodromics." Aha! This is where things get interesting!

For the motor to run efficiently those valves must open and close with fantastic precision. Both their timing and their ability to tightly seal when closed must be nearly perfect. The timing aspect is controlled by a cam, which either directly, or thru a mechanism, pushes the valve open at the correct time. But how to close it? The typical (and simple) answer is a spring. And that is what almost every piston motor in the world uses except those in a Ducati motorcycle. Is there anything wrong with using a spring to close the valve? Yes, plenty.

1) It uses up engine power. To demonstrate this for yourself push the button that opens and closes a ballpoint pen quickly for five minutes and see how your hand feels. Ouch! This despite the fact that the pen's little spring has almost no tension. The springs in a motor, on the other hand, must have a lot of tension because they a) have to keep the valve mechanism against the cam as the motor speedily rotates at up to 12,000+ times per minute. (Care to try to do that with the pen?) And, b) the valve has to seal really, really tight so the expanding gases can't leak out.

2) Because the cam mechanism can't afford to have any 'bounce' from the spring ("boing, boing") the cam profile has to be somewhat gentle. It must gently push the valve, but never shove it. This means the valve must open slowly like a water faucet not quickly like a light switch. In engineering parlance "that sucks."

Enter Italian engineering genius Fabio Taglioni. (Remember that name. It will be on the quiz.) Taglioni looked at the springs in the average motor and said something that could be roughly translated as "What's this shit?"  And then he created the Ducati desmodromic (Greek for "direct activation") system.

Instead of a cam and a spring he reasoned, why not make two cams that can operate in perfect synchronization to open and close the valves. The reason why to most people would have been that odious word: "Perfect." Not to Taglioni. To him perfection was everything. So he got to work. And work. And work. And that, children, is how the Ducati desmodromic engine was born.

How it Works
In the initial designs there were three separate cams shafts,  synchronized together by teeth on their outer rims. One drove the other two and they each operated one motion - opening or closing - of a valve. In time Taglioni came to understand the workings of the desmodromic system  so thoroughly that he was able to design a single cam shaft that, through complex, compound shapes, could open and close both valves and do so with near zero tolerances at virtually any rotational speed.

Are there real benefits to the desmodromic system? Yes! And they are the exact opposite of the spring's shortcomings.

1) With the desmo system there is almost no wasted energy. You can twirl the mechanism of a desmo motor's valve system with your fingers and it'll go round and round, opening and closing almost silently.

2) Because there is no tension and no possibility of 'bounce' in the desmo system, the cam profiles can be as steep as the engine designer wishes them to be. They can thus snap open the valve and then snap it shut. That makes the engine both more powerful and more flexible. It also makes the exhaust note have a unique "Crack!"  Cool, eh?

In the unforgettable words of a famous TV commercial: "That's Italian!"