1984 Yamaha FJ1100

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The 1984 Yamaha FJ1100.
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The 1984 Yamaha FJ1100.
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The scooped belly pan on the 1984 Yamaha FJ100 is classic mid-80s fare.
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Somewhat hidden in all the bodywork of the 1984 Yamaha FJ1100 is the FJ's willing engine, a stout unit producing a claimed 125mph.
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The 1984 Yamaha FJ1100.
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Another classic mid-80s touch on the 1984 Yamaha FJ1100 is the anti-dive braking system.
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Somewhat hidden in all the bodywork of the 1984 Yamaha FJ1100 is the FJ's willing engine, a stout unit producing a claimed 125mph.
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Time has been good to the 1984 Yamaha FJ1100. Clean and muscular, it still has a contemporary look, a hallmark of good design.

1984 Yamaha FJ1100
Claimed power:
125mph @ 9,000rpm
Top speed: 146mph
Engine: 1098cc DOHC 16-valve inline four
Fuel capacity/MPG: 23ltr (6.1gal) / 40mpg (avg.)
Price then/now: $4,999 / $1,500-$4,000

The 1984 Yamaha FJ1100 certainly caused a stir in its freshman year: “The best large displacement sport motorcycle of 1984, and maybe even the best in its class in the history of motorcycling,” said Rider magazine. Cycle Guide made the FJ1100 its Bike of the Year, while Cycle magazine raved, “All hail Yamaha’s FJ1100, King of the Superbikes … class champ, no contest.” So what was all the fuss about?

It’s sometimes difficult to remember there was a time before faired sportbikes. Nakedness was the norm until BMW kicked off the trend with a small, factory-made handlebar fairing on its 1974 BMW R90S, and Ducati launched the street version of the Ducati 750SS — complete with fairing — in the same year. It was another six years, though, before streamline became mainstream on bikes with sporting intentions: think Suzuki’s Katanas and GSs, Kawasaki’s GPz and Ninja range, and Honda’s new V4 Interceptors.

But the bike with the most bodacious bodywork of the early streamlined sportsters was the 1984 Yamaha FJ1100. In fact, its frame was designed with front-end fiberglass in mind, and its shape made the FJ the slipperiest supersport of its day. Along the way, the FJ1100 effectively drew the blueprint for a generation of sport-touring motorcycles — a line that continues today with the Yamaha FJR1300.

Evolution and revolution
The Yamaha FJ1100 that came to the U.S. market for the 1984 model year was a completely new motorcycle. Unlike Suzuki’s entry in this market, the Suzuki GS1100, Yamaha chose not to simply revise its Seventies-era XS1100 engine, starting instead with a clean sheet of paper. Somewhat surprisingly, Yamaha opted for an air-cooled engine with five gears, when both Kawasaki and Honda chose liquid cooling and six cogs for their new supersport bikes. Though simpler, air-cooling inherently limits the engine’s output potential because of inconsistent operating temperatures. That didn’t stop Yamaha engineers from extracting a claimed, class-leading 125hp from the airhead, inline four-banger. Though still an all-new engine, unlike the contemporary Honda V-4, the FJ1100 was evolutionary rather than revolutionary.

In some ways, the FJ1100 bridged the gap between the air-cooled, 8-valve DOHC fours of the Seventies and the new liquid-cooled, 16-valve engines of the Eighties. The FJ1100 also marks a split in superbike development, paving the way for a new class of liter-plus sport-tourers, leaving the out-and-out sportbike competition to the under 1,000cc bikes like the more frenetic Kawasaki ZX9 Ninja of 1984. The split in the superbike market into these niches was new in 1984, and the motorcycle magazines weren’t quite sure how to evaluate them: Were they touring machines, track tools or drag bikes? Or a little of each?

Genesis of the Yamaha FJ1100
The basic Yamaha FJ1100 concept was familiar enough for the time: an inline 4-cylinder engine with double overhead camshafts operating four valves per cylinder. Bore and stroke were conservatively oversquare at 74mm x 63.8mm, but valve sizes, large-ish with 29mm intakes and 25mm exhausts, speak to an engine intended to rev to produce power. Likewise, the four 36mm Mikuni carbs would need to see some pretty rapid pumping to work most efficiently. So this was an engine that had displacement for low-down torque but was also intended to rev to produce its optimum power.

Minimizing engine width was a prime objective, so the generator went behind the crankshaft, and drive to the gearbox input shaft was by means of a gear straight-cut into the no. 3 cylinder’s crankshaft web. The result was an overall engine width of just 20.6 inches. Drive to the camshafts was by Hy-Vo chain from the center of the crank, a one-piece item running in five plain bearings. Supporting those bearings was a cast alloy crankcase, the webs of which were drilled to allow free passage of air between each cylinder. Yamaha claimed this breathing improved power to the “tune” of 5hp!

Behind the crankshaft in the same casing was the multiplate, diaphragm-spring, wet-clutch and 5-speed transmission, the output of which passed to the rear wheel by a conventional 530 chain. Yamaha engineers were also able to keep the engine compact enough for a 59-inch wheelbase.

Less conventional was the chassis. Built from rectangular section steel tubes, the frame’s upper members curved around the engine instead of over it, a pattern now universally adopted for sportbikes (but now wrought in aluminum alloy). The top tubes continued forward around the headstock, meeting in front of it and triangulated to it by short welded tubes. The result was an extremely rigid front end. The peripheral frame structure also allowed the upper fairing to be bolted directly to the frame without using extra brackets or stays, making for a very solid assembly.

Two more frame tubes ran below the engine, but with a bolted-in center section to allow the engine to be dropped out for repair. A sturdy rectangular, extruded-alloy swingarm attached to a single spring/damper unit for rear suspension. At the front was a conventional telescopic fork, set at what would now be considered a relaxed rake angle of 27 degrees (“… steeper than any other current big sport bike,” noted Cycle Guide at the time) and fitted with an adjustable anti-dive device.

This is one of two period features that mark the FJ1100 as a machine of the mid-Eighties: the anti-dive units, one attached to the bottom of each fork, were designed to prevent excessive fork dive under braking. They used hydraulic pressure from the front brake line to restrict fork travel. So the fork would compress normally when hitting a bump in the road, but its compression would be limited when the front brake was applied. That meant the front brake could be used during cornering without unduly upsetting the steering geometry. It certainly improved the performance of the front dampers of the day — though newer forks with variable rate damping have made anti-dive units unnecessary.

The FJ’s other period feature is its 16-inch wheels. Smaller wheels worked well on Grand Prix racers of the era, so why wouldn’t they work on the street? No reason at all, said bike makers — and though the industry switched to 17-inch skins within a few years, the latest racing trend is back to smaller diameters, with Jorge Lorenzo using a 16-incher on the front of his MotoGP ride, a Yamaha YZR-M1.

There’s no question the Yamaha FJ1100 was at least as good as its contemporary competition, especially as an all-rounder. It managed to be ferociously fast, yet docile in traffic, adept at track sessions yet equally at home on tour. In fact, over time it turned into one of the most popular sport touring bikes when the category was just becoming a distinct market niche.

In a six-way Cycle magazine comparison of the best of the 1984 big bikes, the FJ lost bragging rights in top speed (by less than 1mph at almost 146mph) to Honda’s new VF1000F Interceptor, but smoked the field on the dragstrip with a 10.68-second run at a terminal speed of 125.34mph. It achieved all this in spite of weighing more than 570lbs with a full tank of gas, and a power output measured at around 102hp at the back wheel instead of the claimed 125. Its slippery bodywork seems to have been the FJ’s trump card.

In another shootout, Rider magazine concluded that “while the FJ’s performance-oriented ergonomics won’t win any long-distance comfort contests … the result may be 1984’s premier Grand Prix sport-tourer.” MC

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