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Breakthrough: The overhead camshaft – Part two

1 month ago

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David Twohig | Engineer


24 June 2024

In part one, we described the evolution of valvetrain technology, from sidevalves, to overhead valves, and eventually to overhead cams – first single, then double – to give us the ultimate way of opening valves, the ‘twincam’, DOHC or double overhead cam.

But what of the valves themselves? How did they evolve? Let’s dive into the archives and see…

One of the challenges in writing these Breakthrough pieces is to try to decide how far back to go. In the case of valve-gear, we could go very far back indeed. It turns out that James Watt (that Watt who gave his name to the unit of energy) used a valve that looked quite similar to the familiar mushroom-headed poppet valve that we all know and love in his ‘beam engines’ as long ago as 1770. Remarkable to think that the first practical steam engines – those slow-nodding donkeys that drove the Industrial Revolution, freed millions from the drudgery of manual labour (only to enslave millions more in the gears and grime of industrial labour, one could argue) – already used a component that is still vital to the present day.

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