Desmodromic Valves

[legion]

Why are they not used in all high performance engines?

I just heard of them the other day, and they seem like the holy grail of cylinder head technology to me: they prevent valve float.

Because they are not used by many companies (MB used them in the 50's and Ducati uses them now), I'm guessing there is some glaring deficiency in the design that prevents their widespread use.

Edumucate me.

[nostatic]

pita

[notfarnow]

My understanding was that the added weight to the cam & valvetrain offset some of the potential benefits.

I can't remember the details, but I seem remember reading that the desmodromic valves Mercedes used allowed for more aggressive cam profiles, but a lower top RPM

Ferrari desmodromic closeup:

[Aerkuld]

Like nostatic said, bloody complicated ($$$) for most engines and fairly difficult to get them adjusted properly to hold the valve shut without using a spring somewhere. Basically it comes down to the fact that there are better ways of getting the job done, not to say that it isn't cool and makes a nice selling point for the likes of Ducati.

[Jeff Higgins]

They had their day in the sun back before valve spring materials were as refined as they are today. Now they represent added complexity and unnecessary weight. They actually limit RPM's compared to conventional valve springs. The Ducs actaully still use a spring, albeit a lighter one, to fully close the valve. There is some lash that just cannot be removed, that is required to account for varying operating temps and differing CTE's of the various materials in the head and valvetrain.

[HardDrive]

Like Jeff said, they are simply not nessecary anymore. Ultra high RPM applications like F1 engines use some sort of pneumatic solenoids to open and close the valves, thus bypassing the need for any sort of 'valve train' at all. Major weight savings, and allows extremely high RPMs.

[rick-l]

Originally posted by HardDrive
Like Jeff said, they are simply not nessecary anymore. Ultra high RPM applications like F1 engines use some sort of pneumatic solenoids to open and close the valves, thus bypassing the need for any sort of 'valve train' at all. Major weight savings, and allows extremely high RPMs.

I think F1 engines use a pneumatic chamber to close the valve instead of a spring.

wikipedia

[TimothyFarrar]

Chris,

On the topic of cool engine technologies which have gone the way of the dinosaur, check out the Junkers (the same people who manufactured the first turbine jet engine) Jumo 205 engine from WWII. Opposed piston two stroke diesel!

[daepp]

So does the Junkers use 2 crankshafts?

And while we're on the subject, I seem to remember seeing a German airplane engine with the crankcase at the top and heads at the bottom - anyone know anything about it?

[Jeff Higgins]

Originally posted by daepp
So does the Junkers use 2 crankshafts?

And while we're on the subject, I seem to remember seeing a German airplane engine with the crankcase at the top and heads at the bottom - anyone know anything about it?

The Messerschmitts BF 109's ran the engine "upside down". I can't remember offhand who made the engines.

[rob justice]

Originally posted by Jeff Higgins
The Messerschmitts BF 109's ran the engine "upside down". I can't remember offhand who made the engines.

Was it not BMW?

[cashflyer]

BMW made the radials for the FW.
The 109, I think, had a Daimler Benz engine.

edit: here's a link

It appears that the A-C model Bf 109s used Jumo engines, while the D model received a mix of Jumos and DB601s.

[Kirk911SC]

http://en.wikipedia.org/wiki/Daimler-Benz_DB_605