Honda’s RC166 Had More than Met the Eye

Perfection, one hundred percent, ten out of ten—that’s what utter domination looks like, and it also happens to be Honda’s 1966 250cc motorcycle World Championship Series record. With GP racing great Mike Hailwood in the saddle of the incredible RC166, Honda easily secured that year’s rider’s and constructor’s titles, an accomplishment he repeated in 1967. The RC166 would still be a legend today if its only accolades were for competition success and sheer physical beauty, but there’s much, much more to it than that—beneath its delicately shaped fairing and iconic livery there’s a hidden universe of miniature mechanical magic.

In only 250cc Honda managed to squeeze in six tiny cylinders, four cams, and 24 valves the size of pencil erasers. Fed by six diminutive carburetors, it revved to nearly 20,000 RPM and made 65 HP—extrapolated over two liters, that makes for a 48 cylinder, 192 valve, 32 cam, 520 HP motor. In conjunction with a seven speed gearbox, it propelled the RC166’s tiny frame to a top speed of well over 150 MPH. The quality of construction and engineering needed to achieve such amazing complexity and miniaturization is simply mind-boggling, especially considering it came from an age when designers relied on slide rules and drafting tables—the age of computer-aided design was still well over a decade away.

With a crankshaft made of 13 separate components, each no larger than a domino, it was said to be so delicate that it could easily be deformed by hand, yet held up to the astronomical forces exerted upon it when spinning 333 times per second and twisting out the equivalent power of an average Japanese family car of the day. This was only made possible by the use of incredibly precise construction jigs that allowed the crank to be assembled with the kind of accuracy normally reserved for achieving space flight. Ludovic Surcin, designer of the jigs, likened the task to balancing thirteen billiard balls on top of each other and then making sure they stay put.

The engine had effectively no flywheel to speak of, and could rev from idle to past redline with one blip of the throttle, destroying the whole thing in the process. To minimize flex and maximize inertial efficiency, camshafts were barrel shaped, concentrating their mass at the center—this meant that each valve’s geometry varied wildly from one cylinder to the next, with different lobe shapes for each one. Many oil passages are as narrow as half a millimeter, unseen except through the use of x-rays. How they kept the thing running with simple hand tools rather than lasers and microrobotics is a mystery for the ages.

This is the type of engineering excellence that once defined Honda, back in the day when Soichiro was still at the helm of a company he saw as his own personal design playground, before market share and MPG dictated corporate strategy. It’s the Honda whose first-ever car was an F1 machine with a gem-like 1.5 liter V12, whose first road car used an all roller-bearing engine and independent chain drive to the rear wheels, whose use of double wishbone suspension in inexpensive hatchbacks and economy cars made them the first choice among several generations of young enthusiasts. It’s the Honda we miss like an old friend, the one we hope to see again someday soon.

Photo Sources: 1, 2