Saturday, June 11, 2016

Honda V-Four Motorcycles

One of the most influential motorcycles of all time, the Honda CB750, created a serious dent in the competition when released and almost single-handedly caused the British bike industry to stall. It began production in 1969 as the homologation of the Honda CR750. The latter was developed in response to a rule change from the American Motorcyclist Association (AMA) that eased engine restrictions for race qualification, an adjustment that allowed the CR750 to win its inaugural race — the 1970 Daytona 200.

A high-performance powerhouse available to the public, the CB750 is considered by many to be the first superbike. Fit with an air-cooled 736 cc straight-4 engine, a 5-speed transmission, and front disc brakes, the earliest edition harnessed 67 bhp and reached a top speed of 125 mph. With a production run through 2003 and again in Japan in 2007, over 400,000 examples were made. One currently resides in the AMA Motorcycle Hall of Fame.

Thus Honda beat Kawasaki to the punch, since Kawasaki were developing a similar bike. When they realized that the 750 cc bike they had originally been working on would not hold its own against the herculean 1968 Honda CB750, they developed the 903 cc Z1 in response.

Delivered to the public in 1972, the bike featured a double tubular steel cradle that carried an air-cooled DOHC inline-four engine. Releasing 82 horses, the bike could gallop at a top speed of 130 mph while a 5-speed transmission served as bridle.

A synthesis of style and substance, the Z1 also offered an electric start, comprehensive instrumentation, and superior handling characteristics — an innovative combination of brute force and beguiling performance that set a new superbike standard.

This quickly led to copy-cat fours from the other two Japanese manufacturers and bigger models soon appeared (or in the case of Honda … several smaller displacement four-cylinder models: 500 cc, 550 cc, 400 cc, and 350 cc).

As a result, people were becoming bored with straight fours by the 1980s. Although Honda was the company responsible for starting it all with the CB750, now that Kawasaki, Yamaha, and Suzuki were churning out similar bikes — the ubiquitous “Universal Japanese Motorcycle” — it was time for something entirely different.

That something was the VF750S, announced in 1982. Starting with a clean sheet of paper and a blank computer screen, the machine was based around a water-cooled V4 with four valves per cylinder. The two banks of cylinders were set at 90 degrees resulting in almost perfect balance and minimizing vibration. Only the boxer design with 180 degree cylinder alignment could do better.

A quartet of 32mm Keihin carbs was squeezed into the space between the heads. Reving to an astonishing five-figure rpm without stress, this ultra short-stroke engine produced about 80 bhp.

So far, so good. Things began to go wrong when the new V4 was installed in a motorcycle chassis, with the cylinders pointing fore and aft and with a shaft driving the back wheel. Honda included all the latest technology, including Pro-Link rear suspension, flavor-of-the-month TRAC anti-dive forks, and a full set of electronic instruments with liquid crystal gauges. They even fitted the wheels with rims of a decent width.

Which all sounds promising enough, but somehow it was a confused design, an uneasy combination of sports bike and tourer, with an identity crisis. Test reports praised the engine for its power, smoothness, and relaxed feel at speed. On the debit side, the handling was deemed adequate at best, with a sense that the power and weight were overwhelming the suspension.

After Honda’s recent history of a producer of untrustworthy engines (early CX500 and DOHC CB750 and 900 fours, for example), some concerns were raised about the sheer complexity of the V4. This was certainly not a bike for DIY mechanics.

Sales weren’t great from the beginning, but when it became known that all the fears about engine reliability were coming true, the FV750S became difficult to sell at any price. Horror stories about camshafts and cam chains wearing out in a few thousand miles ensured that the bike became something of an embarrassment, helping Kawasaki to sell more straight fours than ever.

Soon the derisive term “chocolate cam shaft” that melted like a candy bar in the hot sun began to haunt the engine. Most of these engines, especially those driven hard, wore out cam lobes, rocker faces, and cam bearing surfaces prematurely. Honda came out with many explanations, excuses, and fixes including:

1. Incorrect valve adjustment because of forked rocker arms.

To avoid this, Honda recommended identical feeler gauges under each fork of the rocker arm at the same time, so the rocker arm doesn't tilt.

This problem is worsened by the fact that the cam caps don't extend very far around the tops of the cams. On the 500cc engines, and the later generation Interceptors, the cam caps extend much farther over the camshaft to hold it snugly in place. This may explain why the problem occurs less frequently in these bikes.

2. Variation in cam-to-bearing clearance because of manufacturing method.

To combat this, Honda developed a special tool to hold the cam in place. The service bulletin issued with this tool recommends valve clearance of .006 inches instead of .005 that the Sabre / Magna originally specified, as well as use of premium motorcycle oil, changed frequently, and avoidance of prolonged idling.

3. Improper cam chain tension.

Various redesigned cam chain tensioners have been developed.

4. Soft cam lobe material.

Later replacement cams use different camshaft material and hardening procedure, so they should last longer than the original cams. Honda offered an extended warranty which essentially meant free cams and rockers whenever needed. This warranty was discontinued in 1989 or so, and it costs about $1000 or so for parts (camshafts and rockers). Such is the cost of poor quality, a theme I’d often sing to my management team in development and manufacturing.

5. Heat

Despite liquid cooling, these engines do get hot. Usually the rear cams are the first to go because they get hottest.

Certainly one key issue was the V4 oil system. The oil system picks up oil from the sump through a strainer and routes it two ways. One goes to the filter and from there to the crankshaft. The other goes to a T joint where one branch goes to the transmission and the other splits again to feed each cylinder head. Therefore the oil is not as clean as it could be. The oil lines are of small diameter. On '83 Interceptors there was a restrictive banjo bolt in the pipes up to the heads. This was fixed for ’84.

Although many fixes were provided by Honda and aftermarket suppliers, this problem continued to plague the V4 until the 90s, with improvements provided over the years. Honda continued to improve the oil system to the camshaft, increasing the size of channels and running the oil down the center of the camshaft.

To address the handling and frame issues, only a year later, Honda fought back with the VF750F, a small change in model type, but a big change in concept. The engine had the same capacity and layout, but it was completely different inside, with a crankshaft turning in the opposite direction and chain drive to the rear wheel. Power was increased to 90 bhp at 10,000 rpm.

Addressing the dynamic weaknesses of the S, the frame was a new wraparound affair made of square-section steel tubes, crazily painted to make it look like aluminum. In addition to RAC anti-dive and Pro-Link rear suspension, the F had another secret weapon — a 16-inch front wheel, which in 1983 was the height of fashion.

The chassis was undoubtedly a good one, and the engine produced a deceptively relaxed rush of power, accompanied by a rumbly background thrum. Aided by an efficient fairing, the VF seemed to be going fast — until the rider looked at the speedometer, when the shocking truth was revealed. There had been plenty of fast bikes before, but doing 130 mph had never felt this easy.

Unlike the S model, the F found plenty of buyers immediately, and for a while, bikes were in short supply. This situation didn’t last long. Despite all the promises, it soon became apparent that the engine was still fundamentally flawed. Camshafts and cam chains still failed after a few thousand miles. After initially blaming everyone but themselves, Honda eventually admitted there was a problem, and became very generous with warranty claims. But it was really too late to salvage the VF’s tarnished reputation. Kawasaki sold even more GPz straight fours in 1983.

Disastrous though it was in some respects, the VF750F herald a new era for motorcycling, one in which bikes became almost too easy to ride at ever faster speeds, without necessarily being any more rewarding, or more exciting. Not everyone appreciated this wimpish new world of effortless two-wheeled travel, so was it a coincidence that sales were slumping, and continued to do so for the rest of the decade.

Ironically the next trend was back to the basic American motorcycle from previous decades. The Harley-Davidson big V-twin bikes with the attempted patent rump-rump (or potato-potato) cruiser sound, and decidedly more old fashioned designs became the trend in the industry.

Soon Honda and the other big Japanese companies began to copy the large V-twin designs, although with many modern accoutrements. (Actually Yamaha was first with the Virago line of cycles.) To this day the large V-twin cruisers and baggers are some of the best selling models for the Japanese companies as well a sales successes for Harley, Victory, and the resurrected Indian brand. These V-twins offer the advantages of narrow engine width and very low seat height, but it is really the sound of that engine that is the key to their success in my humble opinion. That and the movie Easy Rider!

Certainly the Japanese also have sales success with sports bikes that look like fugitives from the Daytona 200 as well as other unique touring bike designs with the Honda Goldwing.

The more complete history of the V-four would include many new models and a steady increase in displacement. The VFR was originally a 750 cc, but became an 800 cc in due course. New models featured technological innovation, such as a single-sided swing-arm, linked braking, ABS, and VTEC. The VFR1200 became the first motorcycle to feature a dual-clutch transmission. Not all of these "innovations" proved popular with riders, who often preferred the simple robustness of the earlier models.

Honda also developed a limited edition VFR, the Honda RC30, as a homologation racing platform. This motorcycle achieved some racing success, but the introduction of very light inline-four motorcycles by competing firms led Honda to downgrade its racing plans.

Honda's VF model line-up had engine capacities ranging from 400 cc to 1,000 cc. Another Honda, the shaft-drive ST1100 also featured a V4 engine, but this touring motorcycle does not form part of the VF series.

The V-four even got caught up in the short tariff war where Harley convinced the US government to add an additional import charge to bikes of 750cc and larger to protect Harley sales. This led to the VF700C model in 1987, which was raised back to 750cc the next year when the tariff was withdrawn.

Under model names of Sabre and Magna as well as the initial Intercepter, Honda produce various models of V-fours up to 1997 and even included a specially equipped police model.

The current standard bearer, an Intercepter model with definite sport bike faring and regalia is described in Honda brochures as a 782cc V-4 VTEC engine with fuel-injection mapping for better low-end torque feel. It includes adjustable seat height to better fit a range of riders, front-mount radiator for a slimmer profile, radial-mount front brakes, and all-side muffler, wheels and Pro-Arm swing-arm. There’s even a Deluxe model for 2015 with features like traction control, anti-lock brakes, self-cancelling turn signals, a center-stand and heated grips.

Self canceling turn signals!?! Doesn’t my ’96 Yamaha Virago have those? And it’s a V-twin. Still I yearn for an ’87 or ’88 “Super” Magna with the four upswept pipes and the little racing chin down under. (That's an '88 VF750C in the picture at the start of this article.) Most of the chocolate camshaft problems were fixed by then, and I’d love to add a V-four to my collection.

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