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The longest-lived engine of all

8 months ago

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Dr Ulrich Eichorn | Engineer


24 October 2023

On 10 June 1963, at the Institution of Mechanical Engineers’ headquarters at No.1 Birdcage Walk in London (at the other end of the same street as Buckingham Palace), Rolls-Royce and Bentley Motor Cars chief engineer Shadwell ‘Harry’ Grylls gave a lecture entitled ‘The History of a Dimension’.

The dimension in question was the bore spacing of 4.15 inches (the distance between the centres of neighbouring cylinder bores) of Rolls-Royce engines used since 1919, and thus on more than 90 per cent of all Rolls-Royce cars and all Bentleys after the Cricklewood era. Bore spacing hardly ever gets quoted outside the engine designers’ papers, yet is the most enduring and defining characteristic of an engine family. Changing it means changing all your machining equipment. It can require a new factory. BMW, for example, for decades had only two different bore spacings (for big and small engines of various cylinder counts); Volkswagen has just one for all its four-cylinder motors.

One morning in 1954, Harry Grylls called lead engine designer Jack Phillips into his office and announced: ‘Our car engine is running out of steam. Go away and think around a 50 per cent increase in power and torque.’ This observation was fair enough given the age of the famed straight-six that had served Rolls-Royce and Bentley for so long. The real challenge was that the new engine should also be no heavier or more expensive to make than the old six.

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