Fifty years ago, a motorcycle engine’s appearance told a story and excited our curiosity, just as did the steam railroad locomotives of my boyhood. We could see functional cooling fins, carburetors, and purposefully angled cam-boxes on bike engines, just as I could see the locomotive’s giant steam cylinders and the whirling and back-and-forthing motions of its long driving rods. Chuck Berry described Johnny B. Goode “strummin’ with the rhythm that the drivers made.” Shapes told stories, revealed functions, stimulated curiosity.
Today, when motorbike engines have become much more powerful yet more efficient, lighter, and longer-lasting, the story told by shape has largely gone quiet. Many engines are concealed behind plastic, and when seen are tall featureless lumps under black epoxy paint. The excitement of clear purpose is hard to discover.
I was excited in 1959 when a friend of my dad opened the hood of his Jaguar 3.4 “saloon,” revealing the angled cam-boxes of its DOHC six-cylinder engine. As Honda’s campaign to win all the classes in FIM Grand Prix roadracing began, spy photos of its succession of world-beating multicylinder engines appeared in magazines, richly clothed in cooling fins, with angled cam-boxes just like Jaguar’s, and with multiple carburetor bells jutting.
Later, becoming involved with racing two-stroke Yamahas, I would stare for long seconds at the dense mass of fins covering heads and cylinders, enjoying their message. Making power from heat requires effective cooling, whether we’re mowing the grass or accelerating into orbit.
We all know perfectly well that today the fins are still there. They’ve just been moved, made thinner, more numerous, and more organized into radiators and oil coolers, tucked behind the front wheel. Honda engineer Shoichiro Irimajiri explained that to cool the hot area above the combustion chambers of his 20,000 rpm Honda GP engines of the mid-1960s the intake and exhaust valves had to be swung apart far enough to make room for a deep maze of cooling fins between them. Cylinders were inclined forward to invite the air to move through those fins.
The needs of efficient combustion have since brought valve included angles down from the 60–80 degrees of 70 years ago to more like 20 degrees now—made possible by the ability of liquid coolants to extract heat from areas inaccessible to air. Now, instead of two cam-boxes, each with its own cover, there is only one, housing both cams. This robs the heads of today’s engines of speech. They have become black boxes.
Included valve angles have decreased dramatically, and now a single less interesting cover houses the entire valve train.
Beauty does exist in engines of the present day, but we must dig for it. Atop each engine is an intake airbox, looking like the most functional of Samsonite luggage. Remove the top and your eyes are gladdened by the sight of multiple intake bellmouths, fuel injectors, a stepper-motor and sensors.
Inside modern motorcycle engines are to be found the grace and beauty that inhabits parts long refined by service at high accelerations. Pistons are foremost here, organic and flowing. Closely coupled are the connecting rods—all the ugly shapes broke, crossing them off the list of possibilities. The valves are shaped by both acceleration and fluid flow.
There’s hope for engine exteriors too. Ducati engineers are heirs to a long tradition of beautifully shaped machines. The close-fitting enclosures of the cam-drive gear trains of Guzzi’s late-1950s liquid-cooled 500cc V8 and those of Ducati’s latest MotoGP V4 are visual celebrations of function that are also entirely functional.
I remain fascinated.