While I was at Robert Iannucci’s Christmas party in Brooklyn over the holidays, I was able to see side-by-side the engineering styles of England, Japan, Italy, and the U.S., as practiced in the three decades following WW II. In the case of production-based engines such as BSA-Triumph’s 1969-75 Triples or Harley’s Sportster-originated XR750, there is the influence of existing tooling. The Dick Mann BSA engine that won Daytona in 1971 is a rococo collection of new and old-style castings, bolted together. They began, not with a fresh triple design, but with what could make most use of existing tooling. British twins housed their cranks in a pair of hemispherical castings, so the Triples consist of a new, plain-bearing center section, to which are bolted right and left case sections with rolling bearings, looking a lot like the two halves of a twin’s case. As with the twins, gear-driven cams are disposed ahead and behind the frighteningly heavy crank (do curls with this thing and in no time you’ll be ready to hold up the earth). Designer Bert Hopwood called such cam drives “rattlers,” and would surely have preferred quieter chains, but tooling was in place and it saved money to use it. Another point was that when Royal Enfield contemplated building a three-bearing twin in the 1940s, they were told that available tooling in Britain was incapable of aligning three bearings.
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In the machine shop was a Benelli 350-4 GP engine crankcase which had just received a new crankshaft. Instead of many castings like the BSA Triple, it has only one—a one-piece monument to “artisanal” pattern making and foundry practice. Everything is contained in it–primary drive, clutch, gearbox, and crank. It’s not split—horizontally or vertically. The pressed-together roller crank’s six main bearings have two forms. In the large case are four main saddles close by bolted-on main caps. At each open end of the case is a bolted-on end plate integral with a cylindrical bearing carrier. The six main bearings have been aligned by pilot honing. All drives come from a gear at crank center, and the engine is 16 inches wide. Such an engine could only exist in a nation of craftsmen. No team manager could ever say of these painfully hand-built creations, “We have 32 engines in the program.” No two such engines would ever be identical. Walk to another plastic-covered bench and you can see a Honda 250-6, disassembled, pending its new crankshaft. Although these are sand castings, lacking the smoothness of production die castings, everything shows the influence of this big company’s design-for-production mindset. Yes, the cast-in-one upper case and finned cylinder block are complex—they were intended to end forever the chronic problem of cylinder base gasket leakage, which had plagued the original RC-160 four-cylinder 250. When we think of a pair of 180-degree twins, end-to-end in one crankcase, the phrase “Two dogs fighting in a sack” comes to mind—for each of those rocking twins badly wants to bust its way out! Ultimately, to avoid the width and weight of a crankcase capable of containing this fight, Honda hoped to build all its fours in Vee form. No more fighting dogs, and three main bearings instead of the inline four’s five or six. For a moment in 1964, Honda chose the inherent smoothness of an inline six (why do you suppose BMW still make them?). 250cc and 297cc sixes won four world championships. QED. Think of how casting cylinder block and upper case strengthens resistance to the rocking couples of the right and left halves of a four- or six-cylinder inline engine. German designer Albert Roder, greatly impressed by the Gilera-four he had seen racing on a trip to Italy, went back to his board to design a proper engine for NSU’s return to GP racing. Modern Top Fuel V8s are disassembled for inspection after every four-second run, and for years they have employed quickly-replaceable cylinder sleeve and piston assemblies. Roder sought something similar by giving his inline R-54 four separate cylinders and separate heads, with each head’s cams driven through couplers by the adjacent head’s cams. It seemed like a good idea at the time, but without the added stiffness of a one-piece cylinder block or head, its crank set its whippy crankcase into frightening flexure that broke major castings, threw parts, and whipped fuel in float bowls into emulsified form that destroyed mixture consistency. There is no NSU in the Iannucci collection, and no contamination of the purity of G-50 Matchlesses and AJS 7Rs is permitted (that is there is no Manx Norton present). Styles of engineering use the differing tools, skills, and traditions at hand to overcome the same basic problems.Gadget Reviews: mamaktalk.com
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