Open and shut case

Keith Howard’s article explaining desmodromic valve-gears in the December 2007 Motor Sport was very interesting, recalling as he does how this type of valve-gear was used for their racing cars by Delage and Schneider in 1914, Rolland-Pilains in 1922 and for the W196 Mercedes-Benz GP cars in 1954.

The French firm of Bignan also employed desmodromics in 1922 for its Cousen 2-litre racing cars, with one of which Gros was third in the Belgium GP de la Marne. The 1923 production 2-litre Bignan retained this valve-gear but apparently it did not add attraction for British customers, because a reliable Trade Directory stated by 1927 that, “we cannot trace that this car is now being imported”, and presumably the Jermyn Street, London premises had closed.

There was also the problem of whether Ernest Henry had toyed with ‘desmodromiques’ for the revolutionary twin-cam, 16-valve, four-cylinder GP Peugeots which won the French GPs of 1912 and 1913, driven by Georges Boillot, and the 1913 Coupe de l’Auto, with drawings only to consult, as none of the Peugeots had survived.

So when Pomeroy was describing the leading GP cars in his book The Grand Prix Car in 1949/1954, he was able to look at the cars owned by VSCC members, but not at a 1912 GP Peugeot, so had to rely on artist L C Creswell’s drawings to determine whether Henry and his accomplices Boillot and Zuccarelli – curiously called “Les Charlatans,” which perhaps they were – had intended to use advanced desmo valve-gear on these 1912 and 1913 Peugeots, which represented a historic step in racing engine design. It took five Mercedes to beat them in the 1914 race, with Boillot visibly distressed as he sat in his Peugeot that would go no further after being driven so hard in his desperate attempt to prevent a German victory.

The question of whether Peugeot ever did utilise a desmodromic design and abandoned it, or didn’t employ it at all, became a matter discussed entertainingly by Pomeroy, Edward Eves, Cecil Clutton, Anthony Heal, W S Bradley, Griffith Borgeson etc, based on the uncertain Creswell drawings of the car.

In the 1920s valve springs were apt to lose their efficiency all too soon, which may be why the great designer and Brooklands racing driver J G Parry Thomas closed the valves of the 1920 Leyland 8 and his highly successful Leyland-Thomas racing cars with leaf valve springs (inset). Thomas also mounted these springs on a rocking base, so that an opening inlet valve helped to close the exhaust valve, and vice versa, a form of semi-desmodromics.

Now, after all these years, the system is serving Ducati well at engine speeds up to 19,000rpm in MotoGP contests, as Keith Howard explains.