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Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>.
Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>. (Robert Martin/)

This is part two of a two-part story. Part 1 appeared earlier this week here.

We continue our appreciation of modern machines as revealed through the tribulations faced by motorcycle designers in the 1950s. Seeing how they overcame them gives valuable insight for the bikes we ride today. Here’s a partial list of their challenges.

  1. Manufacturing, especially in Britain, remained primitive and not well organized. Bikes were more often “crafted” than manufactured.
  2. Most crankshafts spun on rolling bearings of limited life.
  3. Valve springs could break without warning.
  4. Built-up crankshafts could shift at their joints, imposing serious rpm limits
  5. Valve trains were inherently rpm-limited, a characteristic made memorable by the phrase, “My bike may be slow, but at least it’s unreliable.”
  6. Lubricants were short-lived, sludging and gumming easily, especially in air-cooled engines.
  7. Although auto electrical systems worked well, bike electrics acted as if they were still in the prototype stage. Solution? Sacrifice in the temple of Lucas, Prince of Darkness!
  8. Vibration was a constant battle. As one rider put it, “Can’t get some part off your BSA? Go for a ride and it’ll fall off.”
  9. Oil leakage of embarrassing degree, provoking the ironic observation, “If it’s not leaking, it’s out of oil.”
  10. Inadequate cooling. Iron cylinders and heads were suitable for waffling along country roads, but as modern restorers have learned, vintage engines whose cooling can’t keep up with modern traffic quickly reveal their limits.

Valve-Train Evolution

Ducati’s Testastretta DVT engine.
Ducati’s Testastretta DVT engine. (Ducati/)

The British-twin tradition begun by Edward Turner with the original Triumph Speed Twin (1937) was in part made possible by his use of cost-cutting overhead valves (OHV), operated by pushrods and rocker arms (this as opposed to more comparatively complex and expensive OHC, or overhead camshaft, design). The OHV layout allowed the cams to live down at crankshaft level where they were easy to drive and to lubricate, operating the valves via four near-vertical pushrods and head-mounted rockers.

Trouble is, the extra moving weight of more parts, as compared with an OHC design, doubled the valve-spring pressure required to ensure the assembly followed the cam contour.

In today’s drag and NASCAR racing, designers have realized that most of the problems from pushrod valve drive originate in low system stiffness. With open spring pressures of 1,200 pounds, you expect that camshafts dimensioned for spring loads of the late 1950s won’t flex under a 1.5 rocker-arm ratio? Good luck! That’s why today’s aftermarket aluminum V-8 blocks are bored for cams with much larger shaft and bearing diameters. Pushrods have ceased to be dinky metal arrows and are now a hefty half inch in diameter. Rockers no longer teeter on individual slender studs, driven cold into the heads like nails, but are now rigidly supported on long rails. Rockers themselves are proper machined steel parts, not crude 12-cent stampings. The resulting valve trains can follow cam profiles at elevated revs, driven by cam lobes wide enough to maintain the essential oil films. Ducati went through the same process around 1998, resulting in the Testastretta engine whose valve-drive parts (including its cams) were greatly stiffened.

For motorcycles, progress from the pushrod British twins and Harley’s Sportster took the form of double-overhead-cam drive, both lighter and more rigid than what it replaced, making it possible to use cam profiles designed for performance and not just to avoid valve float.

Related: https://www.cycleworld.com/problem-closing-engine-valves-gently/

Lubricating Oil Development

In 1950, lubricating-oil manufacturers were just beginning their work with the multigrade concept: oils made thin enough to cold-start an engine (I well remember the hopeless, slow grinding of the starter motor of my parents’ car in the northeastern winters), but losing less viscosity as oil temp rose in warmup and resulting in adequate load-carrying ability at operating temperature.

Older engines were always full of sludge, a result of oxidation cross linking long-chain oil molecules into “engine gravy.” The situation was so severe that Triumph crankshafts actually featured a sludge trap! The insides of rocker covers were black with the thick mung, and hard-working engines could lose ring seal to gumming and sticking. Detergents, dispersants, and antioxidants were the solution.

Older engines I took apart—a 1930s’ lawn mower, a 1940 Chevy six—had deep ridges at the tops of their piston-ring travel. Such wear would in future be greatly slowed by the development of anti-wear additives such as “TCP” (I was given two explanations of what that stood for—tricresyl phosphate and tom cat piss). What it and other such additives did was form a low-friction solid-lube layer on hot exposed metal. At the top of its travel the piston slows, stops, and reverses, allowing time for the piston rings to sink through their oil films and make metal-to-metal contact with their bores—wear! That wear is much reduced when an anti-wear additive is present in the oil.

The Prince of Darkness

1950s’ electrics were perhaps workable on cars, but the greater vibration present in bikes made life iffy. Would you insulate magneto bearings by pressing them into paper “flowers,” bending the “petals” to surround the outer race? Even installation often sliced one or more petals off—a friend ruined three in a row while rebuilding his Lucas magneto. Corrosion conspired with vibration to create darkness. Japanese engineers, tasked with making trouble-free products that would bring repeat customers, created electrics designed not for Morris Minors and Jowett Jupiters, but for the special conditions on motorcycles. As Cycle World’s own Peter Egan once commented: Saying “someone’s out there in the night on a Triumph” conjures an image of human courage battling inscrutable forces; but to say “he’s out there on a Honda” just told us he’d be here soon.

Self-Disassembly Through Vibration

Traditionally, the two principal weapons in the fight against vibration were low revs (fewer shakings per second) and more weight (the heavier the bike in relation to its pistons, the shorter the “excursion” through which piston-shaking could rattle it). Adding cylinders could help; arrange them right and some self-balancing could occur, as in BMW’s flat twins, Ducati’s 90-degree V-twins, and Triumph/BSA’s 120-degree triples.

Vibration really met its match, however, when balance shafts zeroed out the high-frequency secondary shakes of inline-fours. Secondary vibration was also apparent in the BMW buzz that appeared as the boxers’ pistons grew bigger every year or two, and the otherwise intractable shaking that for so long made it unwise to rev parallel twins of any size much over 7,000 rpm. Until this deliberate smoothing took place, only steel frames could survive the vibratory fatigue. When California optimists tried to graft 450 MX four-stroke singles into cast-off aluminum chassis from timed-out two-stroke racers, their hoped-for new DIY roadracing class was nixed by prompt cracking and failure.

Related: https://www.cycleworld.com/story/bikes/influence-of-engine-vibration-on-motorcycle-design/

Oil Containment

Some of the many other seal types, such as drain-plug and spark-plug washers, O-rings, and soft copper seal rings
Some of the many other seal types, such as drain-plug and spark-plug washers, O-rings, and soft copper seal rings (Jeff Allen/)

Oil leakage is neither a mystery nor unavoidable. It has definite causes and definite solutions. Those causes include:

  1. Poor surface finishes on mating parts (those shaky 1920s’ machine tools and “Monday engines”).
  2. Loss of fastener preload as a result of studs or bolts too short to survive the heat-expansion cycles of their cylinders and heads.
  3. Gasket scrub, resulting from placing those gaskets between parts of widely differing thermal expansion (i.e., an aluminum cylinder head atop a cast-iron cylinder). Remember the “tink…tink” as certain engines cooled? That was one casting slipping against another.
  4. Vibration! A typical inline-four consists of two rocking 180-degree twins that will flex the crankcase, causing gasket scrub at base-gasket level. Honda, in its early 14,000-rpm 250-four roadracers, fixed this by casting the cylinder block and upper crankcase in one self-bracing piece. Rob Muzzy, in building his winning Z1-based superbikes, found that only a solid copper base gasket could survive “engine wriggle” at 10,000 rpm.
  5. Porous, unsound castings leak if you choose your foundry for price rather than performance. The casting revolution that occurred near the end of the 20th century has helped us all.
  6. <i>The Times of London</i> had one and only one advantage as a gasket material—it was available. Japan’s self-bonding black gaskets had other advantages, more useful in oil containment. Durable <a href="https://www.cycleworld.com/story/bikes/seals-in-motorcycles-make-it-all-happen/">double-lipped spring-backed oil seals</a> and O-rings in properly dimensioned grooves have also helped a great deal.

Cooling

Engines require cooling to prevent the heat of combustion and friction from accumulating in any part to the point of damaging it. Plus, the hotter any part of the engine in contact with unburned mixture becomes, the closer that mixture is pushed toward a condition in which it will not burn normally and progressively, but instead detonates—burns at sonic speed, generating shock waves that can blast metal off of the pistons’ edges, eventually exposing the piston rings. For this reason, designers must act to limit piston-crown and combustion-chamber surface temperatures. Also, aluminum loses strength rapidly as it heats up. Another point: Excessive temperature can loosen valve seats or stretch and loosen fasteners. Finally, because all oils lose viscosity as temperature rises, oil must not become hot enough to fail in its key job of maintaining adequate films that keep moving parts from metal-to-metal suicide.

The air-cooled engines of 1950 and later ran hot in summer and cold in winter, and were intentionally jetted rich in order to survive. To cover this temperature range they were also either given thicker oil in summer and thinner in winter, or were run on a single-viscosity oil thick enough to handle summer operation. Compromise, unnecessary power loss, and excessive fuel consumption resulted. Clutch plates, glued together by thick oil, refused to release when cold. Riders paddled with their feet, clunked the trans into first and chugged away.

The transition to stable and controlled year-round operating temperature began with thermostatic liquid-cooling in engines such as Suzuki’s “Water Buffalo” two-stroke triple (1972), and Honda’s “Gold Wing” four (1975). Water, having a density 830 times greater than air, can remove heat intensively. Liquid coolant is also better able than air to remove heat from problem areas such as between paired exhaust valves or surrounding the exhaust ports. Benelli patented an oil cooler in the 1930s, enabling improved control of oil viscosity. Many modern bike engines cool their oil in an oil-to-coolant heat exchanger that is part of the engine’s liquid-cooling system.

Going Forward

Identify problems and admit they exist (this wasn’t easy for traditional manufacturers). Design, test, select, and incorporate successful solutions (this required sales volume great enough to fund such R&D; for example, the long studs adopted in Harley’s Evo engine solved No. 2 above). Understand that continuing development requires evolving solutions. Yesterday’s answer can become tomorrow’s warranty claim.

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Posted
50 minutes ago, Admin said:

Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>.
Kevin Cameron has been writing about motorcycles for nearly 50 years,

 
I think it’s about time he retired.

 

Pleeeeease…….

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