Erudite historians have no doubt looked at the interesting question of when the first ic engine, with’ mechanically operated overhead valves appeared and when such valves were first operated by an overhead camshaft. Leaving aside Ernest Henry’s pioneering of twin overhead camshaft (multi-valve) racing engines for Peugeot from 1912, reference to Gerald Rose points to Fiat having used oh valves, in hemispherical combustion chambers, operated by push-rods and rockers, as early as 1905, which Rose explained “gives more perfect utilisation of the forces of the explosion than any other arrangement”. Pipe had a similar layout in 1904, as had the
Prince Henry Benz of 1908, but with pent-roof heads. It is rather surprising to find that according to Rose many manufacturers were still using automatic inlet valves for racing as late as 1903 and that De Dietrich and Hotchkiss were still using them for this purpose in 1904. Mercedes had, of course, seen the light as early as
1901, with push-rod-operated inlet valves but retaining side exhaust valves, as Renault are thought to have done for their 1902 Paris-Vienna victory.
If Fiat pioneered both valves overhead, in hemispherical heads, soon to be widely copied, although Peugeot’s four valve heads necessitated pent-roof combustion chambers, who first used the hemi-head and oh camshaft? Hugh Conway has shown me an American patent taken out by the two engineers named Welsh of Pontiac, Michigan, in November 1907, for just such an arrangement, albeit possibly intended for gas-engine usage. They had oh valves at 90 deg included angle, operated from a central oh camshaft via rockers, with rollers bearing on the cams. The patent drawing shows a four-cylinder engine with the oh camshaft driven by a vertical shaft and bevel gears from the front of the crankshaft, this drive forming part of the patent specification. All of which suggests a car rather than a stationary engine.
The inventors claimed that the 45 deg inclined valves gave the minimum combustion chamber wall area to swept volume and that the oh valves as located gave a free exhaust and only a slightly heated inlet charge The reduction in valve bounce consequent upon using an oh camshaft in lieu of push-rods was not referred to, but in 1907 engine speed would have been low in normal usage, so that this advantage would have been less apparent. Was this the first ohc engine? I feel sure someone will tell me it wasn’t, and even allowing for time that probably passed between building an engine to the Welshs’ specification (if this was done) and patenting it, Pomeroy was told that Mercedes raced an ohc six-cylinder car with vertical valves in 1907, while by 1908 the fast Clement-Bayard racing cars had inclined valve ohc engines. – W.B.