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Desmodromic Valve Timing Demystified! Insider Look! Forza Ducati!

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Ducati Desmodromic Valve Timing Demystified!

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What are Desmodromic Valves?

The Desmodromic valve system is a type of valve actuation system used in some internal combustion engines, specifically those designed by Ducati, an Italian motorcycle manufacturer. In a traditional valve actuation system, the valves are opened and closed using springs, which can be prone to valve float (where the valve remains open longer than intended) at high engine speeds. In contrast, the Desmodromic system uses a system of rocker arms and cam lobes to open and close the valves, allowing for more precise control over the timing and duration of valve opening and closing.

The Desmodromic system consists of two rocker arms for each valve, one to open the valve and one to close it. The rocker arms are actuated by cam lobes on the camshaft, which rotate as the engine runs. As the cam lobes rotate, they push against the rocker arms, which in turn open or close the valves.

 

Ducati Desmodromic Valves Diagram - How They Work
Example of the mechanics behind desmodromic valves. Courtesy of StackExchange Mechanics user CDunn

[Question of the Day: What’s A More Reliable Bike, Ducati or Aprilia]

What Are The Benefits Of Ducati Desmodromic Valves?

One of the key benefits of the Desmodromic system is that it allows for higher engine speeds and improved performance compared to a traditional valve actuation system. Because the valves are opened and closed more precisely, the engine can run at higher speeds without experiencing valve float. This allows for improved power and efficiency, making the Desmodromic system popular in high-performance engines.

In addition to its performance benefits, the Desmodromic system is also known for its durability and reliability. Because the valves are closed mechanically, rather than relying on springs, there is less wear and tear on the system over time. This makes the Desmodromic system well-suited for use in high-performance engines that are subjected to frequent and extreme conditions.

However, all of this being said, there is much discussion in the engineering community as to the true benefit of a desmodromic valve system.

As with any engine internals, your primary limiting factor is essentially friction alone. Friction creates heat, and excess heat begins a process of material breakdown.

The crux of the argument is at which point do you reach diminishing returns of a desmodromic valve system? For example, the Ducati GP7 revved to an atmospheric 19,000 RPMs without failure.

Ducati GP7

For 2007, MotoGP rules were changed to cap motors to a maximum displacement of 800 cc. In response, Ducati built the GP7. Its specifications were: 800 cc bike, double L-Twin motor (4 Cylinder Twin Pulse).

Ducati started its project to build an 800 cc MotoGP bike extremely early and according to Ducati’s racing chief Filippo Preziosi, by August 2006 Ducati had already built twenty 800 cc engines with various specifications.[3] In addition, an early version of the bike was track tested for the first time during early May 2006.[4] Public testing with the bike began at the Brno Track, where Loris Capirossi had won the day before riding the GP6, on the 21st of August. Capirossi’s lap times on the prototype GP7 were only 1.4 seconds off his track record time set on the 990 cc GP6.

Further testing of the GP7 in Motegi, Japan, revealed that the 800 cc machine could run faster laps than the higher-displacement 990 cc bikes, and held nearly a second advantage over the next fastest 800 cc bike, a Honda ridden by Dani Pedrosa.

MotoGP’s 800 cc era officially began with the first race of the 2007 MotoGP season, at the Losail International Circuit in QatarCasey Stoner won the race on the new GP7. The bike had a clear top speed advantage over the rest of the grid, due to its higher output motor. A new track record was set on the GP7. Second place contender and five time World champion, Yamaha’s Valentino Rossi, realised that “unfortunately, there was too much difference between (our) bikes in the straight” and “Our Yamaha will never go as quick on a straight as the Ducati.” These words turned out to be true, as the GP7 enjoyed a top speed advantage throughout the season, although the other manufacturers (Yamaha, Honda, Kawasaki and Suzuki) closed the gap significantly by the end of the year. Stoner and his Bridgestone-shod Ducati proved to be the top combination in MotoGP and he won the world championship at Motegi, Japan, on September 23, 2007, four races before the end of the season.

Ducati Desmosedici – Wikipedia
Example of the mechanics behind desmodromic valves. Courtesy of StackExchange Mechanics user Ceshion

Are Desmodromic Valves Used Outside of Ducati Motorcycles?

Funny that you ask, I found myself asking the same question. The answer is YES, there were actually desmodromic valves present in Mercedez-Benz F1 cars prior to Ducati’s, essentially, full transition to the desmo system.

Predominant examples of desmodromic valves, outside of Ducati, being the Mercedez-Benz W196 and Mercedez-Benz 300 SLR. As of this time, the desmodromic F1 valve systems have been ushered out for a more optimized pneumatic valve system.

Desmo Valves Vs. Pneumatic Valves

Ahhhh, I see you’re asking the right questions.

As we discussed, your primary limited factor for any mechanical part is friction and the heat that is subsequently generated. As time went on, the F1 development teams realized that desmo valves created more friction and carried more weight. In essence, this meant that desmodromic valves were actually less effective than other alternatives.

How Do Pneumatic Valves Work?

In Formula 1 cars, pneumatic valves are used to control various functions such as engine throttles, gear shifts and suspension adjustments. These valves use compressed air, supplied by on-board air compressors, to actuate mechanisms that perform the desired function.

The basic principle of a pneumatic valve is to control the flow of compressed air into a chamber, which in turn actuates a piston or diaphragm to perform a specific function. In the case of an engine throttle, for example, the valve controls the amount of air that enters the engine, which in turn controls the engine’s speed.

Pneumatic valves in Formula 1 cars are typically operated by an electronic control unit (ECU), which receives signals from various sensors on the car, such as throttle position sensors and gear position sensors. The ECU then uses this information to control the pneumatic valves and adjust their settings accordingly.

Formula 1 cars use different types of pneumatic valves, including poppet valves, spool valves, and pilot-operated valves. Poppet valves are the most common type of valve used in Formula 1 cars, and they consist of a cylindrical valve stem with a disc-shaped end that seats against a valve seat to control the flow of air. Spool valves are similar to poppet valves but instead of a disc-shaped end, they have a cylindrical spool that slides inside the valve body to control the flow of air. Pilot-operated valves are more complex than poppet and spool valves, they have a pilot valve that controls the main valve, this allows for faster and more precise control of the flow of air.

Overall, pneumatic valves are an essential component of Formula 1 cars, as they play a critical role in controlling various functions and enabling the car to perform at its highest level. The technology used in Formula 1 cars is constantly evolving and improving, with teams constantly experimenting with new types of valves and control systems to gain a competitive advantage.

Photo by Stephan Louis on Unsplash

New Ducati V4 Granturismo Engines don’t use desmodromic valves, what gives?

Yes, you read that right. The V4 Granturismo will not use a desmodromic valvetrain. Before metallurgy advancements in the 1950s, desmodromic valve systems held an advantage over spring valve return configurations when applied to engines destined for continuous high-rpm use. In the early days of racing, springs of that era could not withstand the abuse of sustained high-rpm, resulting in “valve float,” as well as catastrophic failure. 

Ducati V4 Granturismo Engine Revealed: No Desmodromic Valves | Rider Magazine

Yes that’s right.

Basically, Ducati has increased the service intervals for valve adjustments. This was a huge cost of ownership for Ducati owners, regularly desmodromic valve services every 7500 or 12,000 miles.

In the early days, Ducati was able to capitalize on their use of desmodromic valves because early-day valve springs would fail under heavy load due to inferior metallurgy at the time; however, modern metallurgy has “caught up” which allows Ducati to use valve springs in their V4 engines to ease the cost, and further convenience, of modern Ducati ownership.

At the end of the day, it does come down to money though, doesn’t it?

Why Ducati Switched Valve Systems

Ducati made the change from desmodromic valves to conventional valves in its V4 engine for a few reasons.

Firstly, Desmodromic valves require more precise manufacturing and assembly, which can be more expensive. Using conventional valves allowed Ducati to reduce the manufacturing costs associated with the desmodromic valve system.

Secondly, the Desmodromic valves are heavier than the conventional valves, this added weight could be an issue when it comes to high-performance motorcycle, where weight is a crucial factor.

Thirdly, conventional valves are less complex than desmodromic valves, which means that they are more reliable and require less maintenance. This is particularly important for Ducati, as the V4 engine is used in both road and track-oriented motorcycles.

Lastly, Ducati engineers were able to extract more performance out of the conventional valves, this led to the improvement of the V4 engine’s power output and torque.

Overall, the change from desmodromic valves to conventional valves in the V4 engine was a strategic decision made by Ducati to reduce costs, improve reliability, and increase performance.

Summary

Overall, the Desmodromic valve system is a key technology that has contributed to the success of Ducati and helped to establish the company as a leader in the motorcycle industry. Its precise control over valve timing and duration, combined with its durability and reliability, have made it a popular choice in high-performance engines around the world.

Learn more about the wonderful world of Ducati!

Or even better, learn some more through a full breakdown of Ducati desmodromic valve systems

https://www.youtube.com/watch?v=aqxNZ0LzRFU

For questions or concerns, please use the comment fields below!

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-The Seasoned Wrench

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