Breakthrough: The overhead camshaft – Part three

The patience of the Ti tribe seemingly knows no limits. Having tested it thoroughly with writing not one, but two articles about the obscure origins of the overhead cam and multi-valve heads in Edwardian machine-shops (well, strictly speaking they were French ateliers and hence more Belle Époque than Edwardian), certain among you asked for yet more punishment in the form of further historic trivia about valve gear. Hard to believe, I know, but here we go.

For the sane among you, feel free to click ‘Next’ and I’m sure there will be some gem about a fast Porsche, or wise words about how not to crash from Steve Sutcliffe.

The specific ask from the hardcore engineering geeks – yes, they walk among you – was to cast light on the origins of ‘variable’ valve systems. A fair question – so far, we’ve treated the good ol’ poppet valve as if it were a simple disc popping open and closed. And of course it’s a far more involved beast than that. Have a good look at one – hold it up to the light if you will – and you will see that the form of the underside of the valve’s head is quite complex, with the stem blending smoothly into a complex concave-to-convex curve, terminating in the chamfered edge that (hopefully) seals it nicely into the cylinder head valve seat.