Motorcycles and Steam Locomotives

Not so much engineered as shaped by conditions

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Technical Editor Kevin Cameron shares his wealth of motorcycle knowledge, experiences, insights, history, and much more.Cycle World

I’ve been reading a lovely 1952 book about the evolution of steam locomotive technology, and as I’ve turned the pages, I’ve been struck by its similarity to the motorcycle’s technical evolution.

In both cases, technologies that engineering said ought to work often either just did not, or produced no significant improvement.

Marine steam engines became more efficient when steam was expanded through two or more cylinders by 'compounding'. Compound locos were built with high hopes but higher maintenance tended to erase any fuel savings. And when superheated steam was tried, it boosted efficiency with acceptable costs. Above all, rail locos had to be rugged and easily serviced; that eliminated many complex solutions.

In the 1970s and ‘80s it was assumed that radical new concepts – especially those coming from Formula One – would transform what were conceptually glorified 1905-era motorized bicycles into something of real sophistication. We can list dozens of such experiments, some pursued with serious R&D clout, but none has changed the basic nature of the motorcycle.

There was innovation in locomotive design, but only if it survived the pounding of over-the-road use. That made its evolution gradual rather than revolutionary. Many alternative designs were tried, but only durable, effective solutions survived.

Locomotive frames began as complex fabrications of many parts, but at every point of assembly – bolts, welds, or machined fits - weakness lurked. The eventual solution was to cast the steam cylinders and valve bodies in unit with the frame beams – in extremely durable cast steel.

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In 1997 I went to England to see the new V8 "Norton Nemesis" (it came to nothing) and saw that it had a cast magnesium chassis. Here was the leading edge of significant change, but I didn't see it at the time. A new casting method, often based upon low-turbulence bottom-fill techniques, was producing cast parts with close-to-forged fatigue properties. Very soon, Yamaha began to use the similar Hitachi process to cast its aluminum frame elements, eliminating most of the dozens of welds that used to join cast, extruded, machined-from-solid, and sheet elements into a chassis. Simplicity outperformed complexity.

Every engineer can see the problems with telescopic forks; their sliding action invites upsetting stick-slip motion, their angled mounting makes them pro-dive during braking, and their stress path makes no sense at all – starting with front tire grip at pavement level, stress is carried by long, bendy fork elements up to the high bicycle-style steering-head, only to then be redistributed downward again into the main structure and engine. Yet every attempt to devise a more rational front end for motorcycles has been defeated by the developed example of established practice. The simplicity of the bicycle continues to define the motorcycle.

In similar fashion, steam engineers knew that fire-tube boilers were archaic in comparison with the modern water-tube variety so well-proven in marine and stationary service. Batches of locos with water-tube boilers were built, but proved expensive to maintain in the face of roadbed hammering. Fire-tube boilers were no picnic, but they were maintainable; when a loco came in from a run, its fire was dropped, planks were thrown onto the fire grate, and a man in heavy protective gear clambered into the firebox, where he used a soapstone crayon to mark leaking fire tubes (leaks were easy to see – each one was jetting steam at 380F). Later, other men would caulk those leaks with pneumatic hammers. A fresh fire was set and the machine went out on the road again.

Structures engineers see that an aircraft fuselage has maximum stiffness from minimum material because it is a large thin-walled tube. Again and again, ‘monocoque’ motorcycle chassis have been built on this principle, but there were problems. First, motorcycles need longitudinal bending stiffness to withstand braking force, but need lateral flexibility to act as a crude but useful suspension at high lean angle. Single beam chassis were stiff in all directions, and also interfered with maintenance. They were not a practical solution so they are seen no more.

Both the steam locomotive and the motorcycle are vehicles shaped, not by cutting-edge technology, but by what can be made to work reliably and well. They are above all practical. This is why, at the races, crew chiefs are experienced at the job. They are seldom engineers. Engineers know what ought to work, and their contribution is real and continuing. But someone must then adapt what the engineers build to the realities of use in ever-changing conditions, in the hands of a unique human rider.