Engine Design Converges

[Hugh Janus]

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

When I had accumulated some ­basic experience as quite a young man, I realized there were clear ­national styles in motorcycle engines, but in this new century, I see such ­diversity receding in favor of a new ­international style.

I saw that British designers ­reacted against oil leakage and Times of ­London gasket material by employing a multitude of screws to hold case covers in place. Examples are the attractive, polished timing covers of British twins, but the extreme is exemplified by the cam covers of the Rolls-Royce Merlin aircraft V-12, secured by nearly 30 fasteners each. Also very British was too few crankshaft main bearings—as in giving a parallel-twin or even an ­inline-four just two of them, and “­lettin’ ’er flex” in jump-rope fashion. Also ­essentially British in nature was the assumption that a taper alone, without key or other form of angular ­location, could be trusted with ignition timing. Assemble the taper loose, align crank and magneto as desired, then give “a sharp rap with a small hammer and do up the nut. She might move a wee bit in the first gallop or two, but then she’ll bed in.” Muddling through.

German design, by considerable contrast, was a demonstration of the extreme capabilities of that nation’s machinists, often requiring the use of liquid nitrogen in the performance of shrink fits. Where a British crankshaft was assembled with tapers and nuts (all of the classic singles were thus) and was then aligned by soft hammer and dial gauge, a German crank such as that of the Adler two-stroke twin was aligned by finely machined ­radial face splines, drawn together by another favorite: a differential-threaded bolt. German design also ­reflected the extreme physical rationalism of Bismarck’s higher technical universities—that design must begin always from first principles. In my shop is the gap-bed lathe from the German Type-IX U-boat U-873. It is a tour de force of triple security on major assemblies, a multitude of clutches, and rigidity that comes only from aged cast iron.

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The evolution of American motorcycle design practice stopped in 1913 when Henry Ford’s Model T took the transportation market. Only two years before, high-tech Indians with dog-ring gearboxes had swept the Isle of Man TT 1-2-3. From such creative fluidity American design solidified into slow-turning, large-displacement iron engines in heavily built bikes that could survive in a land of dirt roads. That style was enshrined as right and proper—the American way.

Italian motorcycle engine design has been a conflict, with sensuous organic design and the shrink-wrapping of major castings suggesting the mysteries within, versus a contrary impulse to style every crankcase as a massive rib-reinforced ­aluminum egg. I loved the cam-drive wheel case of the Guzzi V-8, and the dense finning of Mondial’s Rebello, then wondered why so much aluminum was poured to make each Ducati bevel-drive engine.

Spain, a nation new to manufacturing, struggled to produce its ­early Montesas, OSSAs, and ­Bultacos. Not everything was always as it should have been. From a Bultaco ­service bulletin came advice on how to ­combat oil weeping through porous castings: Remove and ­completely dismantle the engine. Then with a ball-peen hammer, the reader was to compress and seal the entire inner surface of the cases by tapping. Improvisation rules. Yet it was ­Bultaco, combining dead-simple two-stroke engines with extreme lightness, who triggered the mass market for ­off-road riding.

Motorcycle Engine Architecture (Jim Hatch/)

Now much of that national ­design individuality is shifting—toward what I am calling an “international engine style.” An early indicator was the ­engines made for John Bloor’s new Triumph motorcycles. Many called them “English Kawasakis” ­because they appeared in black epoxy finish with shapes closer to modern Japanese practice than to anything from Triumph’s Edward Turner past. In ­recent years, the more new engines I’ve seen, the more they come to ­resemble each other rather than continue the distinct national styles of the past. It was particularly striking to look at the details of Indian’s new PowerPlus big twin, which could have been those of any number of other engines I’ve seen recently.

Why should this be so? Around the year 2000 came a casting revolution. Older methods, ­producing fewer sound parts that ­consequently had to be made heavier for ­adequate strength, were replaced by bottom-­fill, low-turbulence methods that produce castings so much ­freer of defects and voids that they have near-forged properties. On a ­before-and-after basis, complete ­motorcycles shed over 30 pounds of excess weight and all welding was automated. There has also been convergence in assembly methods. Out with the old—assembly workers with screw guns—and in with ­completely hands-off simultaneous fastener installation and final torquing. Cases are sealed by robotic pens that write a continuous line of sealant immediately before crankcase closure.

To conserve material and ­control weight, major castings fit intimately over the parts they enclose ­rather than being styled into Philippe Starck eggs. Coolant passages are held tight to keep liquid velocity and heat transfer high.

Just as Moto2 teams have ­discarded chassis that, while fast, are difficult and time-consuming to set up in favor of those that handle competitively over a broad setup range, so manufacturers have discovered which automatic production systems are most productive, cheapest to operate, and throw the least scrap. This pushes each factory to resemble all other factories.

Variety in engine architecture ­remains (as you can see in “Old Souls,” page 58), but beneath it is a sameness.

Design for production requires that whatever design choices are made, they must not be allowed to complicate or add costs to manufacturing. In the 1970s, former ­Cycle magazine editor Cook Neilson watched an early CNC machine take half an hour to machine each Ducati twin con-rod, and we learned that the proper adjustment of each bevel-­gear cam drive required seven hours’ work by an experienced technician. Market competition made human handwork too expensive to remain a part of production.

Quality today far exceeds ­anything from the honored past, but to combine it with never-ending advanced features and still hit the price point, production methodology and ­economics must rule.

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