Leaf valve springs.

John Godfrey Parry-Thomas was a Welsh engineer and motor-racing driver who at one time held the land speed record. While chief engineer at Leyland Motors, he designed engines with leaf springs instead of coil springs to close the valves. One of those arrangements is shown in the first photo below. Coil springs were prone to breaking in those days. He had some trouble with his leaf springs too, but took his idea a step further, as shown in the second photo below. In the early 1920’s, he actually designed a proper desmodromic valve gear. Although it looks similar to his earlier leaf spring design, it is very different. The leaf spring only acts as a helper spring. Even today, Ducati finds helper springs necessary in its Desmo engines. I do not know if Thomas built any engines with this desmo valve system. A very clever man.