Yamaha XJ550 Seca
Claimed power: 50.46hp (rear wheel) @ 10,000rpm (period test)
Top speed: 110mph
Engine: 528cc air-cooled DOHC inline four
Weight: 424lb (with half-tank fuel)
Price then/now: $2,529/$1,300-$2,700
If the test of a good design is longevity, the XJ engine line must be considered one of the best. In continuous production from 1980 to 2008, the air-cooled, eight-valve DOHC inline four has been available around the world in 400, 550, 600, 650, 750 and 900cc form.
The first XJ was the 650, launched in 1980, with the 550 joining it a year later. More than just a 650 on a diet, the Yamaha XJ550 Seca was essentially all new.
Unlike the 650, which used gears for primary drive, the Seca 550 crankshaft drove a hydraulically tensioned Hy-Vo chain to a jackshaft carrying the clutch and alternator. The jackshaft provided gear drive to the 6-speed transmission, which, unlike the stacked shafts of the 5-speed 650, was laid out horizontally. And while the 650’s final drive was by shaft, the more sporting 550 used a chain. A conventional steel tube frame and swingarm ran on cast alloy wheels fitted with a single front disc brake and rear drum. Also conventional was the non-adjustable front fork, with dual shocks (adjustable for preload) at the rear.
The novel cylinder head design featured Yamaha’s YICS induction control system. Cast into the head was a second, smaller set of intake ports connected across all cylinders, so that each cylinder received two simultaneous charges of fuel/air mixture — one from its own intake port, and one at much higher velocity from the YICS “sub-intake” port positioned just above the valve head. The idea was to create extra swirl in the combustion chamber and therefore more efficient combustion. Did it work? The Seca 550’s test fuel consumption of 53mpg suggests it did.
The Yamaha XJ550 Seca was also well-equipped, with features you’d expect only on bigger, costlier bikes: self-canceling turn signals; a clutch/neutral electrical interlock that prevented the Seca being ridden away with the sidestand down by killing the engine if you shifted into first before lifting the stand (routine now, but new at the time); an adjustable front brake lever; and a warning light that showed low oil level rather than low pressure. The idea was that the owner got a warning to top up the oil in the wet sump before it got so low that oil pressure was lost — a potential engine-saver.
The Seca 550 punched above its weight on the strip, too. Period tests achieved standing quarter-mile times below 13 seconds and a top speed of 110mph. That kind of performance was 900cc Superbike territory a decade earlier. Power delivery was progressive, but with a real rush over 6,000rpm and with power peaking at 10,000rpm. So the engine liked to be revved, but it was also reported to be docile in traffic.
On the road, the Seca 550 was smooth in operation with a large, comfortable seat, light controls and the ability to spin along easily at highway speeds. It made a useful tourer, too: both the seat and the gas tank were good for at least 150 miles. That said, the suspension worked better for solo riding than two-up. Steering and handling were sporty rather than racy, with a fairly fast 27-degree rake, but the undercarriage would ground well before tire traction ran out. Though quicker around the track than many competitors, the Seca had to concede top class honor to the tauter, more powerful GPz550.
But the charm of the Yamaha XJ550 Seca lay in its good-natured rideability, lively performance, quality construction and grin factor. Said Cycle World in April 1981, “Around here … the test bike didn’t wait long. Someone was always ready to ride it away.” Added Rider in its May 1981 report, “The Seca 550 is an exciting motorcycle. There’s no need to qualify that with ‘for a 550’ or ‘for a bike this size.’ It goes great, stops well, handles sensationally and is easy to live with day to day.”
A good recipe then, and still a good recipe today.
Contenders: Half-liter rivals to the Yamaha XJ550 Seca
Claimed power: 54hp (rear wheel) @ 10,000rpm/116mph
Engine: 553cc air-cooled DOHC inline four
Weight: 459lb (half-tank fuel)
Price then/now: $2,500 (1981)/$1,500-$3,000
The GPz was the bike to catch in the 550 class in the early Eighties. Introduced in 1981 with air-charged front forks and a conventional twin-shock rear suspension, the 1982 model featured Big Green’s single-shock Uni-Trak system, helping it win Cycle World‘s Bike of the Year in the 451cc-650cc class.
Based on the 1980 KZ550, the Kawasaki GPz550 offered a lot more go. Period tests on the dyno showed a power boost from 43hp to 54hp (58hp by 1984), accomplished by increasing compression from 9.5:1 to 10:1 and installing bigger valves and hotter cams. However, the engine needed to be revved above 7,000rpm to get that extra boost, resulting in just 45mpg (eight fewer than the Yamaha XJ550 Seca) when ridden hard. Powerful dual front discs replaced the KZ’s single stopper, which had been found lacking by testers. A single disc (8.9in, same as the front) took care of the rear.
A useful feature of the GPz, especially for newbies, was an interlock preventing the shifter moving from first to second with the bike at a standstill, making neutral selection a snap. In 1982, along with the Uni-Trak rear, the Kawasaki GPz550 gained an oil cooler, voltmeter and LCD gas gauge, while losing five pounds. In shootouts, the GPz usually came out tops in its class. That is, until Honda’s VF500F arrived in 1984 …
Claimed power: 53hp (rear wheel) @ 11,000rpm/132mph (1984 model)
Engine: 498cc liquid-cooled DOHC V4
Weight: 419lb (dry)
Price then/now: $2,898 (1984)/$1,500-$3,000
Based on the Europe/Japan market VF400F, Honda’s half-liter entry offered all the sophistication of its bigger brother, the VF750F (including air-assist Pro-Link suspension and anti-dive fork; see The First Sport Bike? The 1983 Honda VF750F Interceptor), in a nimbler, more compact package. The 60mm x 44mm V4 screamed all the way to 12,000rpm, with a flat torque curve that made for relaxed around-town riding.
Testers praised the VF’s quick steering, attributing much of that to the 16-inch front wheel, yet also admired its straight-line stability and supple suspension. The Honda VF500F aced most comparos with other 550cc bikes, turning a 12.4 second standing quarter-mile at 107mph. Using all the VF500’s power, though, would push its fuel consumption well below 40mpg. Though the Kawasaki GPz550 got four more horses in 1984, the Honda VF500F maintained its performance edge.
But there was trouble in paradise. A spun rod bearing in Cycle Guide‘s 1984 test bike was followed by crankshaft failures in the field, prompting a major recall that involved replacing entire engines. Though not all Interceptors were affected, Honda fitted milder cams and smaller carbs to 1986 VF500s. This moved the powerband down the rev range and trimmed a couple of ponies from its top-end, but added mid-range pull. It fixed the problem, and Cycle concluded the changes made the Honda VF500F even better. MC
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