In his excellent just-published book about MG cars, reviewed elsewhere, Wilson McComb says, quite rightly, that when the M-type MG Midget was conceived, Cecil Kimber had a ready-made overhead camshaft engine for it, in the guise of that designed for a still-born Wolseley Eight in 1927 and used in detuned form for the new Morris Minor. This engine, says McComb, was derived from the post-WW1 Wolseley Ten via the war-time W4A Hiapano-Suiza areo-engine, which Wolseley had built under licence during the war.
This is, of course, broadly true and there is no doubt that in building these vee-eight aero-engines the Wolseley Company became familiar with the problems of designing and making o.h.c. engines. But, as I have pointed out previously in a special article on single-overhead-camshaft engines and also in the history of the Brooklands’ racing Wolseleys which appeared in Motor Sport during 1968, there were differences between the Wolseley Viper aero-engine and the o.h.c. Wolseley car engines, some of which had chain-drive as well as vertical-shaft drive for the camshaft, and all of which in pre-WW2 form had rockers of one sort or another interposed between camshaft and valves. Incidentally, on some of these engines tappet adjustment was effected by means of rotating eccentric bushes within the rockers.
When MG brought out the 18/80 Six-cylinder model it was said that Cecil Kimber had again used a conveniently-available Wolseley o.h.c. power unit, but McComb makes it clear that what Kimber actually based the 18/80 MG engine on was an o.h.c. Pendrell-designed JA-type Morris engine which was used in 1927 in the Morris Light Six and subsequently in the Morris Six and Morris Iris cars. This engine also had rockers, not the Hispano-Suiza direct-onto-the-valves actuation, and the camshaft was chain-driven.
What I find interesting is that Wolseley, who might have been expected to be the first to crib the brilliantly simple Marc Birkigt Hispano-Suiza layout, did not do so until the advent of the post-WW2 4/50 and 6/80 Wolseley engines, which followed it closely, even to retaining the vertical-shaft-drive for the camshaft. So the query arises, why did it take more than 30 years for someone at Wolseley’s to appreciate the merits of the Birkigt design (l will not argue here whether it was more suitable for aero-engine or car-engine application) and who was that person ? After all, other people had copied the Birkigt valve gear so far as the rocker-less direct-action was concerned, notably, as we are reminded on page 1254, the Stutz designer in America, and it is seen today on Vauxhall Victor, Rover 2000. Triumph Dolomite, Austin Maxi, Fiat 128, Hillman Imp, etc.
Another aside is whether, in fact, the 1920 Wolseley Ten was inspired by the Viper, or that it just happened that its designer favoured an o.h.c. engine, for others of the smaller car engines, such as the Dawson and Bugatti were using an overhead camshaft at the time, as did the Singer Junior some years later. — W. B.