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Bentley camshaft drive – Why we love...

Bentley camshaft drive – Why we love... Classic and Performance Car

Pre-war Bentleys featured an elegant and intricate solution to cam timing.


You’re in the 1920s before almost-silent cambelts were invented, a sequence of bevel gears is too noisy and you don’t trust a chain to drive the overhead camshaft of your new, hefty, ultra-refined six-cylinder motor. What do you do?
 
If you’re WO Bentley and your new Speed Six has plenty of underbonnet length, you think steam locomotive wheel-driving system and your engine ends up with not one but three crankshafts. Your near-silent system uses three slender connecting rods to join cranks, spaced 120º apart, on the end of the camshaft to those attached to a helical-tooth gearwheel driven at half crankshaft speed by another on the crankshaft’s rear end. Using three rods rather than one keeps rotation smooth and stress-free.
 
It’s a bulky and slightly mad idea, the sort that arrives in a dream or in the bath. It appeared on the 8 Litre, too, then Rolls-Royce took over and it was Not Invented Here. Shame.
 
Words: John Simister

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