According to Ricardo (1927) the Clerget rotary engine had a solid cylinder with head and two vertical valves operated by rockers. The Bentley rotary had a detachable head and a steel cylinder with an aluminium casing with fins on the outside. The valves are also vertical and operated by push-rods. This cylinder construction, according to the Science Museum Handbook on Engines (1936), was patented by R. Ayton in 1898.
The Clerget was built in England by Gwynnes, in 1916-17, 130 h.p. (120 x 160) and 150 h.p. (120 x 172). The Bentley (1917) 150 h.p. (120 x 170) and (1918) 200 h.p. (140 x 180) was made by Humber. The weights quoted for the 150 h.p. model are 400 for the Clerget and 408 for the Bentley.
The original Gnome rotary engine had two valves (the “monosoupape” came later). The Clerget came later. The Rhone rotary of 1913 was the first engine of this type with two positively-operated valves, again vertical.
Any good designer worth his salt picks up where others have left off—in time of war it is his clear duty. It is left to historians afterwards to find fault with this process.