47 replies to this topic

[TerryS]

I have been reading about this valve system and I am intrigued.

 

It seems it was first patented in 1896, so it has been around a long time.

 

I see it was used in the Mercedes Benz W196 F1 car of 1954-55 and their 300SLR sports race.

 

However I can't see any use in race car engines since.

 

Ducati developed the system for their Moto GP bikes and won many world championships with it. 

 

So why is it not more extensively used?

[HP]

Desmodromic valves can be traced back to Richard Küchen's K-motors in 1924, the 1949 Norton Manx was also before Mercedes. Ducati's first bike with desmo was built in 1950 too.

 

The advantage is that the engines could rev higher.

 

The disadvantages and why it hasn't been used that often is that there are many more mechanical parts that needed careful maintenance. It also made the engine heavier and particularly in bike racing that can be a disadvantage.

 

Another issue is that the additional parts required more room, which wasn't good for anything more than 2 cylinders. Ducati made the 4 cyl. Desmosedici. The adjustment time for the Desmocedici's 16 valves is said to be around 7 hours! Yikes!

 

Obviously these days, except for branding purposes, injection and better build quality of engines render the desmo to the sidelines.

 

I heard the sound of these original SS-900 bikes from one kilometre away passing by me. It's one exquisite big sound spectacle to my ears. Unfortunately not for everyone though. Other 90 degree 2 cyl engines due sound nice, I even owned a Moto Guzzi Monza, but the Ducati SS-900 was on another level in the sound department. The desmodromic valves give a very distinct sound pattern.

Edited by HP, 10 June 2022 - 03:53.

[GregThomas]

It was used on the F1 Scarabs but it's heavy and complicated - certainly compared to pneumatic valve return systems.

 

When two valve per cylinder engines were at the top, there was certainly a case for using it. Once lighter four valve per cylinder arrangements became the norm, the limiting factor on revs moved from the valve train to the crank/rods/pistons again.

 

Ducati use it because they've tied themselves to it. They certainly appear to have mastered it so it's no handicap. Unlike the situation a few years ago where Yamaha had tied themselves to five valve layouts. Took a few years before they could move away from that without loss of face.

[Tim Murray]

Cosworth seriously considered using desmodromic valve operation on the DFV in the early 1980s. Keith Duckworth was quoted on it in Graham Robson’s Cosworth book:

We got a programme going in the early 1980s, it didn’t copy anyone and it was an original concept and layout. We built parts and tested them on rigs. But I stopped the programme, and I made myself fairly unpopular. I thought it was all going on for too long, and after I had worked out all the sums for the stressing, I came to the conclusion that we couldn’t actually build something of this type that would be strong enough. It kept on failing, and I felt I was vindicated, but some of the engineers thought they could make it work. I thought that my analysis of the problem was reasonable. Either it was never going to work, or it was going to require too much development and redesign to make it work. It was going to need a fundamental redesign, which would throw it right back in time. I wasn’t prepared to sanction that ...

My understanding is that BRM considered desmodromic valve operation on the Type 25 in the 1950s, and Ferrari also looked at it in around 1990/91.

[Vitesse2]

My understanding is that BRM considered desmodromic valve operation on the Type 25 in the 1950s ...

Unusual decision for BRM to reject the complicated and more difficult option.
 

[a_tifoosi]

I just came across this website: https://www.desmodro...ustion-engines/

Recently I finished reading Sébastien Faurès Fustel de Coulanges's fantastic book on Fiat ("Fiat en Grand Prix - 1920-1930") and, indeed, one of the early engines (401? can't recall it right now) used desmodromic valves.

Another interesting case is Arthur Michelat's 1914 Delage Type S.

[Ray Bell]

There's interesting discussion on this topic in the W196 section of The Design and Behavior of the Racing Car, in the ....Pomeroy section of that topic...

 

I think it's the Delage which was mentioned there, and that they used light springs for the final valve closing, but soon found that the light springs would fail. But the valves still closed and remained closed due to gas pressures despite this, and that Mercedes had found the same thing in experimenting with their engines.

 

They did have valvegear problems, IIRC, at either Monaco or the Spanish GP or both, the former in 1955 and the latter in 1954.

 

By the eighties, Bruce Cary told me, the Honda engineers had reached a point where the bottom end could be spun up to incredible revs reliably, but the limiting factor was a kind of wave action in the valve springs. Renault, of course, soon fixed that.

[plannerpower]

Setright, in Some Unusual Engines, says that the 1911 GP Delage had desmodromic valve operation; I have only found one on-line reference to this, at;

 

https://velocetoday....history-part-1/

 

where it is said that;

 

Michelat was brilliant; his work for Delage would include designs for twin ignition, four valves per cylinder, desmodromic valves and five speed transmission. Michelat’s Type X race car was a three liter four with two plugs per cylinder, four horizontal valves per cylinder, lubrication via pressurized oil pump, and a Claudel constant level carburetor.

 

This implies, but doesn't clearly confirm, that the 1911 Type X Delage had desmodromic valve gear.

 

Delage experts will know, I'm sure.

[Michael Ferner]

The Type S Delage had desmo valves, not so sure about the X.

[Roger Clark]

I just came across this website: https://www.desmodro...ustion-engines/

Recently I finished reading Sébastien Faurès Fustel de Coulanges's fantastic book on Fiat ("Fiat en Grand Prix - 1920-1930") and, indeed, one of the early engines (401? can't recall it right now) used desmodromic valves.

Another interesting case is Arthur Michelat's 1914 Delage Type S.

It was the 401. The 801 car only raced twice, Parma-Poggio di Berceto and the Targa Florio in 1921. Fiat won both but not the 801. They did not enter the 1921 Grand Prix de l'ACF although the 801 was eligible. Later that year they brought out the 802; its 402 engine was very different from the 401: 8 cylinders instead of 4, 2 valves per cylinder instead of 4.

Faurès Fustel de Coulanges also says that Bignan had desmodromic valves at the 1922 Grand Prix de L'ACF de Tourisme.

[Charlieman]

I'd look back a little further before the convention of springs and mushroom/poppet valves. In the hand cranking days, it was common to have a mechanical lift device on the inlet valve. Metallurgy and springs weren't great in those days.

[Allan Lupton]

I'd look back a little further before the convention of springs and mushroom/poppet valves. In the hand cranking days, it was common to have a mechanical lift device on the inlet valve. Metallurgy and springs weren't great in those days.

Yes the recognition that the atmospheric inlet valves limited engine speed. therefore power, gave us the mechanically operated inlet valve and it took engineers such as Fred Lanchester to take advantage of that system to open the valve for longer than the AIV could. However they retained springs to close the valves, in some cases with an additional bit of mechanical help which was not really true desmodromy.

[Roger Clark]

There's interesting discussion on this topic in the W196 section of The Design and Behavior of the Racing Car, in the ....Pomeroy section of that topic...

 

I think it's the Delage which was mentioned there, and that they used light springs for the final valve closing, but soon found that the light springs would fail. But the valves still closed and remained closed due to gas pressures despite this, and that Mercedes had found the same thing in experimenting with their engines.

 

They did have valvegear problems, IIRC, at either Monaco or the Spanish GP or both, the former in 1955 and the latter in 1954.

 

By the eighties, Bruce Cary told me, the Honda engineers had reached a point where the bottom end could be spun up to incredible revs reliably, but the limiting factor was a kind of wave action in the valve springs. Renault, of course, soon fixed that.

It was Monaco.  All three cars retired for the same reason, failure of a small screw in the valve mechanism.  The same design had won the Mille Miglia but Karl Ludvigsen speculates that the higher raving Grand Prix engine may have encountered vibrations which caused the failure.

 

The M196 system was nicknamed Zwangsteuerung, or Z-Steuerung for short (Z-Drive in English).The design was sketched by Hans Gassmann on the back of an envelope on the trolley bus home from work one evening.  The design was transferred to engineering drawing and a copy sent to the Daimler-Benz patent lawyers who found that Delage (as mentioned above) and Th. Schneider had positively closed valves in the 1914 Grand Prix.  They also found the Bignan sports cars.

 

In September 1950, Motor Sport published an article by Balladeur (Kent Karslake) on cars with Desmodromic valve.  He quotes a letter in La Vie Automobile from Baron Petit in which he claimed that the single cylinder Aries racer built for the Grand Prix des Voiturettes of 1908i not only had ” induction by mixture previously compressed to a pressure higher than that of the atmosphere “—in other words some kind of supercharger–but also ” four valves per cylinder desmodromically operated by an overhead camshaft.”

[JtP2]

My understanding is that BRM considered desmodromic valve operation on the Type 25 in the 1950s, and Ferrari also looked at it in around 1990/91.

Bob McIntyre of motor cycle fame was working on desmodromic valve gear in his workshop for BRM when he was killed. So BRM were always thinking complex. An H16 with 4 desmodromic valves per cylinder? Seems right up BRM's street.

[Bloggsworth]

No one seems to have mentioned peugeot:

 

https://i0.wp.com/ww...tery1.jpg?ssl=1

Edited by Bloggsworth, 10 June 2022 - 21:09.

[john medley]

One Aries in 1908 GP de Voiturettes had not just desdromony but mild supercharging as well.

[Roger Clark]

No one seems to have mentioned peugeot:

 

https://i0.wp.com/ww...tery1.jpg?ssl=1

For many years it was believed the the 1912 Grand Prix Peugeot had desmodromic valves.  This was perpetuated by a drawing of the valve gear in The Grand Prix Car.   However, neither Pomeroy nor Creswell had seen one of the cars. The theory was debunked by Borgeson in an Automobile Quarterly in the early 80s. I haven’t got that edition of AQ  but Borgesen’s arguments were summarised by Boddy in Motor Sport. 
 

However, the drawings in the link posted by Bloggsworth don’t relate to the 1912 Peugeot and I can’t see evidence of desmodromicity in any of them. 

Edited by Roger Clark, 10 June 2022 - 23:04.

[Bloggsworth]

For many years it was believed the the 1912 Grand Prix Peugeot had desmodromic valves.  This was perpetuated by a drawing of the valve gear in The Grand Prix Car.   However, neither Pomeroy nor Creswell had seen one of the cars. The theory was debunked by Borgeson in an Automobile Quarterly in the early 80s. I haven’t got that edition of AQ  but Borgesen’s arguments were summarised by Boddy in Motor Sport. 
 

However, the drawings in the link posted by Bloggsworth don’t relate to the 1912 Peugeot and I can’t see evidence of desmodromicity in any of them. 

That's me told then...

[Michael Ferner]

The M196 system was nicknamed Zwangsteuerung

Zwangssteuerung (with two "s") is the German word for desmodromicity (that a word? )

[Roger Clark]

You can have no idea how difficult it was to get my English speaking Mac to accept that word, then you have to tell me I still got it wrong.  

Edited by Roger Clark, 11 June 2022 - 17:25.

[Michael Ferner]

Well, if your mac can speak, surely you can talk reason to it... 

[Bikr7549]

That word was always a bit mysterious to me. Here is the Wikipedia explanation of its entymology.

„The word comes from the Greek words desmos (δεσμός, translated as "bond" or "knot") and dromos (δρόμος, "track" or "way"). This denotes the major characteristic of the valves being continuously "bound" to the camshaft.“

[Adrian Beese]

Did BMW built a f2 car with a desmo engine and chassis constructed by Dornier or has my memory finally given up

[Ray Bell]

I believe that one was 'different' because of the displacement of the valves...

 

They were dispersed radially.

[Michael Ferner]

Apfelbeck stagger valve design, not desmodromic.

[Roger Clark]

In around 1956, the Maserati brothers experimented with desmodromic valves in the OSCA Tipo TN.  I don't know how much it was used.

[2F-001]

Did BMW built a f2 car with a desmo engine and chassis constructed by Dornier or has my memory finally given up

As Ray and Michael have said, it had the inlet and outlet valves diametrically opposed - so that, although a straight four, it had four inlet trumpets and four exhausts on each side of the head. This, or a similar configuration to the F2 engine, also appeared in the BMW hillclimb car the 'Monti'/'Bergspider'/G767** (chassis built by Lola?  **delete as per preference).

 

I think the Dornier-built F2 chassis were later replaced by Lola-built ones - or was it the other way around?

Edited by 2F-001, 12 June 2022 - 16:29.

[a_tifoosi]

For many years it was believed the the 1912 Grand Prix Peugeot had desmodromic valves.  This was perpetuated by a drawing of the valve gear in The Grand Prix Car.   However, neither Pomeroy nor Creswell had seen one of the cars. The theory was debunked by Borgeson in an Automobile Quarterly in the early 80s. I haven’t got that edition of AQ  but Borgesen’s arguments were summarised by Boddy in Motor Sport. 
 

However, the drawings in the link posted by Bloggsworth don’t relate to the 1912 Peugeot and I can’t see evidence of desmodromicity in any of them. 

 

AQ Vol XX, No 3 from July 1982. "Twin Cam, Amen. Some Post-Publication Discoveries to Round Out the Historical Record". 

I imagine that I am not allowed to upload the article. If anyone wants an scanned copy, please let me know.

 

 

Narcís. 

[a_tifoosi]

It was the 401. The 801 car only raced twice, Parma-Poggio di Berceto and the Targa Florio in 1921. Fiat won both but not the 801. They did not enter the 1921 Grand Prix de l'ACF although the 801 was eligible. Later that year they brought out the 802; its 402 engine was very different from the 401: 8 cylinders instead of 4, 2 valves per cylinder instead of 4.

Faurès Fustel de Coulanges also says that Bignan had desmodromic valves at the 1922 Grand Prix de L'ACF de Tourisme.

 

Thanks! Now that I have the book in front of me, I observe that there's a very detailed explanation of the desmodromic operation on page 39. The corresponding patent, GB154875A "Improvements in and relating to the valve-gear of internal combustion engines", can be found here.

 

Narcís.

Edited by a_tifoosi, 12 June 2022 - 19:36.

[Roger Clark]

AQ Vol XX, No 3 from July 1982. "Twin Cam, Amen. Some Post-Publication Discoveries to Round Out the Historical Record". 

I imagine that I am not allowed to upload the article. If anyone wants an scanned copy, please let me know.

 

 

Narcís. 

Thanks.  I've got AQ Vol XX, no 3.  However, Boddy said the article he was referring to was in Vol XXIX No 3. It seems that he two articles cover much the same ground.  I have to confess that I'm confused by the plethora of drawings showing L-shaped, D-shaped and finger tappets and how they relate to different engines of the time but it seems clear that no Peugeots has desmodromic valves.

[Roger Clark]

As Ray and Michael have said, it had the inlet and outlet valves diametrically opposed - so that, although a straight four, it had four inlet trumpets and four exhausts on each side of the head. This, or a similar configuration to the F2 engine, also appeared in the BMW hillclimb car the 'Monti'/'Bergspider'/G767** (chassis built by Lola?  **delete as per preference).

 

I think the Dornier-built F2 chassis were later replaced by Lola-built ones - or was it the other way around?

I don't think the Apfelbeck engine had inlet and exhausts on each side.  The inlet ports were vertical, making the engine look like a V8 at first glance.  The engines were used in 1967 in Lola T100 chassis by BMW (entered as BMWs) and by Lola Racing (ie John Surtees). Surtees himself usually drove an FVA engined car but he did achieve the BMWs best result, second in the Eifelrennen.  BMW later produced an F2 engine with inlets and exhausts on each side but the Apfelbeck principles had been scrapped.

 

Karl Ludvigsen's Classic Racing Engines contains a chapter on the Apfelbeck.

[Ray Bell]

I wasn't sure, Roger, but I just did a bit of an image search on Google and there were a couple of layouts...

 

In both, the inlets and exhausts came out both sides, though the inlets in one version were more of a downdraught setup.

[Michael Ferner]

Ludwig Apfelbeck had the so-called "radial four-valve" configuration patented in the mid thirties, at a time when such engines already existed (e.g. 1930 Rudge, 1931 Frontenac*). He worked for Horex, Maico and KTM before BMW, and of course his work included more than just this one theme. But mention of an "Apfelbeck design" usually refers to "radial" or "stagger" valves.

 

 

* I think the first such design was built by Fiat in the very early teens, but am not sure. Robert Dick will probably know.

Edited by Michael Ferner, 13 June 2022 - 12:08.

[2F-001]

I believe that BMW used at least two different layouts, with the most obvious visual differences being - as Ray points out - the disposition of the inlet trumpets.

 

My (limited) understanding of the layout ascribed here to Apfelbeck is that inlets and exhaust valves are radially (or 'diagonally') opposed - (or alternating around a circle if you like) in a hemispherical combustion chamber, for the thermal, swirl, or other efficiencies thus gained.

With inlets and exhausts thus being on both sides of the cylinder, it seems inevitable - indeed unavoidable - that inlet trumpets and exhausts would be on both sides of the head, whether the inlets are near-upright on the top or angled and more from the sides.

 

Roger - you said that Apfelbeck principles were dropped on the later F2 engine but that it had that similar kind of layout; are there, then, some other aspects of the Apfelbeck design that I've missed or not understood?

 

Most of the images I have relate to the hillclimb cars rather than the F2s. (And I don't have Karl's book. Perhaps I should...)

Edited by 2F-001, 13 June 2022 - 13:44.

[Roger Clark]

I believe that BMW used at least two different layouts, with the most obvious visual differences being - as Ray points out - the disposition of the inlet trumpets.

 

My (limited) understanding of the layout ascribed here to Apfelbeck is that inlets and exhaust valves are radially (or 'diagonally') opposed - (or alternating around a circle if you like) in a hemispherical combustion chamber, for the thermal, swirl, or other efficiencies thus gained.

With inlets and exhausts thus being on both sides of the cylinder, it seems inevitable - indeed unavoidable - that inlet trumpets and exhausts would be on both sides of the head, whether the inlets are near-upright on the top or angled and more from the sides.

 

Roger - you said that Apfelbeck principles were dropped on the later F2 engine but that it had that similar kind of layout; are there, then, some other aspects of the Apfelbeck design that I've missed or not understood?

 

Most of the images I have relate to the hillclimb cars rather than the F2s. (And I don't have Karl's book. Perhaps I should...)

I certainly didn't intend to imply that later F2 engines had a similar kind of layout.  The Apfelbeck engines had the valves radially opposed as 2F-001 describes and downdraught inlet ports, the only option.  The valve gear was complex and heavy.  It was initially installed in a Brabham F1 chassis for testing and record breaking, later in a Lola for the European mountain championship.  At this time it was 2-litres.   In 1967, a 1.6-litre version was used in F2 but it was rarely competitive with the FVAs. BMW dropped out of F2 for most of 1968 although Hahne drove a Lola with 2.1-litre version in the German Grand Prix.  BMW re-entered F2 with a new engine and Lola chassis (T102).    This engine abandoned the Apfelbech principles and had alternate inlet and exhaust ports along each side of the engine.  Inlet and exhaust ports were both side draught. I believe that Apfelbeck had by this time left the company following disagreements with the hierarchy. 

 

You should get Karl's book.

Edited by Roger Clark, 13 June 2022 - 14:36.

[uechtel]

Image search on google for "BMW Apfelbeck" delivers some illustrating pictures.

[Ray Bell]

The complication was greater because of the angles at which the valves operated...

 

It would be simple if the valves were all inclined in rows, as 4-valve arrangements typically are, but they are set radially so that the valve heads form a part of the 'hemisphere' of the combustion chamber.

 

There must surely have been some mechanical loses in the rocker gear, at least compared to regular OHC layouts, while the claimed benefits (and I'm sure they were real to a point) of cool air flowing over hot exhaust valves and the ability to swirl the gases in there didn't make up for all the complication.

[Michael Ferner]

That's how I see it, too. Advantages, yes, but at the price of increased complexity. Net gain, perhaps slightly south of zero?

[Roger Clark]

If I may return briefly to the subject of desmodromic valves...

 

Early in this thread I referred to the long held theory that the 1912 Peugeot GP engine used the system.  This apparently originated from an article by Charles Faroux shortly after the race.  It was given weight by a Cresswell drawing in Pomeroy's Grand Prix Car (page 128 of my edition).  It was endorsed by writers of the calibre of Cecil Clutton (in The Racing Car, written with Cyril Posthumus and Denis Jenkinson), William Court (in a Classic Car Profile) and Griffith Borgeson (in The Classic Twin Cam Engine).

 

Borgeson later came to the conclusion that the theory was nonsense and that the Cresswell drawing was, to put it mildly, fictitious. his arguments were summarised by Boddy in Motor Sport March 1987.  Boddy said that Borgeson's article appeared in AQ Vol XXIX, no.3.  I have now discovered that it was actually in Vol XXIV no.3 - did someone say Pity the Poor Historian?  Vol XXIV also contains a long article by Borgeson on the Type S Delage which did have desmodromic valves.  

 

Even the most recent of these sources is now over 35 years old.  I would be interested to know if there has been any more recent research that adds to the story.

Edited by Roger Clark, 14 June 2022 - 10:35.

[Doug Nye]

Nobody has yet mentioned Hispano?

 

DCN

[a_tifoosi]

 

Borgeson later came to the conclusion that the theory was nonsense and that the Cresswell drawing was, to put it mildly, fictitious. his arguments were summarised by Boddy in Motor Sport March 1987.  Boddy said that Borgeson's article appeared in AQ Vol XXIX, no.3.  I have now discovered that it was actually in Vol XXIV no.3 - did someone say Pity the Poor Historian?  Vol XXIV also contains a long article by Borgeson on the Type S Delage which did have desmodromic valves.  

 

 

Interestingly, in the Delage Type S article by Griffith Borgeson, I've found the following text: "The principle is as old as the slide valve on an ancient steam engine. In the case of poppet valves, it is as old as a Daimler patent of 1883. Henri Petiet, who was associated with the Aries company at the time and therefore active in voiturette racing, told me that he remembered a desmo engine in the Coupe des Voiturettes de l'Auto of 1910. He was unable to recall the marque or the specific solution employed". It seems that M. Petiet didn't recall that Ariès had already used desmodromic valves by 1908.

 

 

Even the most recent of these sources is now over 35 years old.  I would be interested to know if there has been any more recent research that adds to the story.

 

I don't have it, but there's an article by Sébastien Faurès Fustel de Coulanges and Henk Cloosterman on the 1908 Ariès in The Automobile, June 2015: https://www.theautom...ssue-june-2015/

 

 

Narcís.

[Roger Clark]

Nobody has yet mentioned Hispano?

 

DCN

Can anybody tell me more?

[Roger Clark]

Interestingly, in the Delage Type S article by Griffith Borgeson, I've found the following text: "The principle is as old as the slide valve on an ancient steam engine. In the case of poppet valves, it is as old as a Daimler patent of 1883. Henri Petiet, who was associated with the Aries company at the time and therefore active in voiturette racing, told me that he remembered a desmo engine in the Coupe des Voiturettes de l'Auto of 1910. He was unable to recall the marque or the specific solution employed". It seems that M. Petiet didn't recall that Ariès had already used desmodromic valves by 1908.

 

 

 

It was a Beron Petiet. who wrote to La Vie automobile in 1921 about the desmodromic Ariès,

[a_tifoosi]

It was a Beron Petiet. who wrote to La Vie automobile in 1921 about the desmodromic Ariès,

 

 

Thanks! Henri [Marie] Petiet, mentioned in Borgeson's article, was the brother of Charles Petiet —Baron Petiet and founder of Ariès.

Edited by a_tifoosi, 15 June 2022 - 10:34.

[robert dick]

No desmo-head in Delage X:
The 3-litre Coupe de l'Auto Delage type X of 1911 and the 6,2-litre Grand Prix type Y of 1913 had no desmo-heads.
Both engines had two low-mounted camshafts operating horizontal valves via pushrods and rockers, two valves per cylinder in the type X, four valves per cylinder in the type Y.

= = = =

Fiat valve arrangement:
The 10-litre Fiat tipo S61 of 1909/-10 and the 14-litre tipo S74 of 1911/-12 both had a single overhead camshaft and four vertical valves per cylinder. The intake and exhaust pairs were disposed transversely, each pair being operated by a bridge piece. There was an intake and an exhaust valve on each side of the head (not crosswise).

= = = =

Ariès:
The Petiet/Ariès/mentioned by Kent Karslake page of La Vie Automobile/1921:
http://cnum.cnam.fr/.../577/80/620/0/0

= = = =

The Théo Schneider of the 1914 French Grand Prix, described by William Bradley,
Motor Age/Chicago/30 July 1914 and The Automobile/New York/30 July 1914:







 

[a_tifoosi]

Fantastic, Robert  !

 

The Théo Schneider of the 1914 French Grand Prix, described by William Bradley,
Motor Age/Chicago/30 July 1914 and The Automobile/New York/30 July 1914:

 

In "Automobiles Peugeot. 1888-1918 L'eclosion. Le visionnaire et les createurs" by Bernard Derelle there's a chapter dedicated to Gratien Michaux. There's no reference to the desmodromic valves of the 1914 Th. Schneider, but it includes a long list of patents. There's one, from 26 November 1913 and entitled Mécanisme de commande des soupapes des moteurs à explosions à grande vitesse (it can be found here), that most probably was the basis of the Th. Schneider desmo-head.

 

Narcís.

[Roger Clark]

The patent drawings show greater to similarity to the 1955 Mercedes than to the contemporary Delage. 

[barrykm]

Fascinating, but bedevilling to my non-technical mind