Yamaha FJ1100 – The Supersport Smoothie
It’s sometimes difficult to remember there was a time before fully enclosed sportbikes. Naked was the norm until 1974 when BMW fitted a small handlebar fairing on its R90S, and Ducati launched the 750SS. It was another six years though before streamline went mainstream on bikes with sporting intentions: the Suzuki Katanas, Kawasaki’s GPz and Ninja range, and Honda’s new V4s.
But the most bodacious bodywork of the early streamlined sportsters belonged to the 1984 Yamaha FJ1100. Its frame was even designed with front-end fibreglass in mind, and the shape made it the slipperiest supersport of its day. Along the way, the FJ1100 effectively drew the blueprint for a generation of sport-touring motorcycles right up to the FJR1300.
The FJ1100 certainly caused a stir: “The best large displacement sport motorcycle of 1984, and maybe even the best in its class in the history of motorcycling,” said one enthusiast magazine, while another made the FJ1100 its Bike of the Year, and yet another raved, “All hail Yamaha’s FJ1100, King of the Superbikes … class champ, no contest.”
Rather than simply revising its 1970s-era XS1100 motor, the FJ1100 was a completely new motorcycle. 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 motors. Though simpler, air-cooling typically limits the engine’s output potential. That didn’t stop Yamaha engineers extracting a claimed, class-leading 125 hp from the airhead, in-line four-banger. So, while still being an all-new motor, and unlike the contemporary Honda V-4, the FJ1100 was evolutionary rather than revolutionary.
In some ways, the FJ bridged the gap between the air-cooled, eight-valve DOHC fours of the ‘70s, and the new liquid-cooled, 16-valve motors. From another perspective, the FJ marks a split in superbike development, paving the way for a new class of litre-plus sport tourers, leaving the out-and-out sportbike competition to the under 1000cc bikes, like the more frenetic Kawasaki ZX9 Ninja. 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?
THE BASIC FJ CONCEPT WAS FAMILIAR enough for the time: a four-cylinder in-line engine with double overhead camshafts operating four valves per cylinder. Bore and stroke were a conservatively oversquare 74 by 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 a motor that had displacement for low down torque, but was also intended to rev to produce its optimum power.
Minimizing engine width was a primary 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 number three 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 centre 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 five horsepower!
Behind the crankshaft in the same casing was the multiplate, diaphragm spring wet clutch and five-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 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 centre 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,” said one reviewer.), and fitted with an adjustable anti-dive device.
This was one of two period features that mark the FJ as a machine of the mid-1980s: 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. 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 were its 16-inch wheels. These worked well on Grand Prix racers of that era, so why wouldn’t they work on the street? And though industry switched to 17-inch hoops soon after, the latest racing trend is back to smaller diameters, with Jorge Lorenzo using a 16-incher on the front of his Yamaha YZR-M1.
There’s no question the FJ’s performance 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. And over time Yamaha’s FJ series became some of the most popular sport touring bikes of the era.
– Robert Smith, September 2009 (issue #255)