The Human Touch

  • AUTHOR
    American Honda
  • POSTED
    Jan 08, 2013
  • POSTED IN
    The Open Road

A river of technology runs through motorcycling—a looping, unpredictable and unrelenting torrent with hip-deep engineering problems that spawn organic and imaginative solutions. Just as the singular demands of long-distance touring forced Honda to define new objectives to create the Gold Wing, so did engineers have to adopt a whole new way of thinking to address the Gold Wing’s primary goal: unparalleled long-term touring comfort. This two-part series covers the Gold Wing 1000 through the Gold Wing 1500, and the driving force of touring riders in their development.

Touring riders are quite vocal about their likes and dislikes. As a result, the Gold Wing has marched in lockstep with the desires and objections of its owners. The Gold Wing created touring as we know it, but like a smoothly polished river stone, both the bike and the market have been shaped by customers over the years.

The Gold Wing 1000’s shortage of roll-on punch reflected Honda’s less-than-crystal-clear focus on what the bike should have been. Although engineers wanted the Gold Wing tuned for maximum torque and a broad powerband, Honda management also knew what worked in the mid-’70s marketplace: peak performance. A quick fix was to re-gear the engine to spin faster, but this easy approach increased both vibration and noise. A better solution was to spread the power, shifting the torque peak down to coincide with engine rpm at 60 mph. That’s precisely what Honda did to the Gold Wing’s engine for 1978.

Boosting roll-on acceleration is more easily accomplished with increased displacement, and that’s the path Honda chose for the Gold Wing’s first major redesign in 1980. Bumping displacement to 1085cc, engineers reconfigured the cylinder heads for better combustion at low and middle rpm, and shortened gearing slightly to bring engine speed and peak torque closer together at 60 mph. Following this trend, the 1982 Gold Wing received taller ratios for third, fourth and fifth gears to lower cruising rpm further. In 1983 Honda fitted a taller primary drive ratio, and the result made for even more relaxed engine speed at 60 mph.

Coinciding with the introduction of the 1984 Gold Wing 1200, other touring models were appearing, but Honda was well ahead of the competitive curve. The development team specified more displacement, 1182cc to be exact. Careful tuning boosted midrange and top-end power, and new final-drive gearing produced the tallest overall gearing yet for the Gold Wing. Performance took a big jump in 1985. The Gold Wing 1200 Limited Edition benefited from shorter overall gearing and fuel injection, which provided magnificent throttle response. Once again Honda shortened the Gold Wing’s primary gearing, but fitted a taller gearbox ratio for fifth, so engine rpm at 60 mph went up only slightly. Though fuel injection continued with the 1986 Aspencade SE-i, its high cost forced Honda to return to carburetors for 1987.

By this time, the Gold Wing’s venerable horizontally opposed four-cylinder engine was reaching the end of its productive capacity. As an engine is made bigger to raise its torque and spun slower to reduce noise and vibration, its firing impulses become bigger and spaced farther apart; this is felt as driveline harshness. The solution to smoothing the engine’s power flow was clear: increase the number of cylinders from four to six. With the introduction of the ground-breaking 1520cc Gold Wing 1500 in 1987, the all-new flat-six was re-geared to turn more slowly, yet still delivered substantial passing punch.

A large engine, turning at low cruising rpm, was just the beginning of an overall process of noise and vibration suppression for the newest Gold Wing. Osamu Sato, the noise, vibration and harshness (NVH) engineer on the Gold Wing 1500, surveyed the entire motorcycle for noise with microphones and waveform recording and analysis equipment. For example, a subtle sawtooth wave might come from gear teeth engaging under power. Or a barely detectable low-frequency signal might come from the crank’s motions in its bearings. Once these sound sources were understood and quieted, the refinement process was incorporated into design and production. For fifth gear, a quieter-running helical pair was substituted for the original straight-cut gears. Extremely close crank-to-bearing tolerances hushed the crankshaft journals.

Tracing the history of the Gold Wing’s powertrain reveals another trend that is distinct to Honda motorcycles: the utilization of automotive design elements. On the original Gold Wing 1000, automotive-style liquid cooling maintained consistent engine operating temperature, allowing for closer production tolerances that resulted in more power and longer engine life. An added benefit was that liquid cooling muted mechanical engine noise considerably. A related bit of automotive technology was the Gold Wing 1500’s liquid-heated intake manifold. By heating the intake manifold with coolant and using the exhaust manifold to heat intake air during warm-up, the fuel from the carburetors evaporated more readily, forming an easily ignited air/fuel mixture that reduced hesitation.

Yet another bit of auto technology is the Gold Wing’s shaft drive. The Gold Wing was Honda’s first shaft-driven production motorcycle, and drivetrain engineer Hirotake Takahashi pioneered uncharted—and tortuous—engineering ground. The gear pair connecting the driveshaft and rear wheel had to be bulletproof. Drag-strip starts, missed shifts and pothole impacts subjected these gears to great loads. In addition, the gears would also have to be as silent as possible. Takahashi devised an ad hoc gear-torture protocol called the hop test to simulate the worst of what might happen in actual use. A test rider would ride at about 30 mph, shift to neutral, and then stomp the transmission into first. The rear wheel would slam violently against the pavement, impacting as many as 20 times in rapid succession. This hopping effect exerted up to two tons of thrust force and 3.5 tons of lateral thrust on the gear teeth, cracking gear cases like eggs. Endless combinations of material, tooth pitch and form, heat-treating and surface-hardening methods and depth were tried. All of them failed. Takahashi eventually realized that the gear case was flexing, concentrating the immense loads at the fragile edges of the teeth and causing the failures. Improved gear case designs followed, and with more testing, his engineers soon produced Honda’s first reliable motorcycle shaft drive.

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