Honda CB 550SC Nighthawk

The Little Cruiser with Power!

Everybody likes power, whether they prefer their handlebars wide and tall or narrow and low, and some of the biggest skirmishes in the horsepower war are being fought in the 550 class.

Which introduces the Nighthawk 550, Honda's horsepower entry in the non low-bar 550 market, a bike with cruiser styling and high performance.

There's no mistaking the styling-there's chrome everywhere, a short chrome front fender on long, leading-axle forks; chrome headlight, carburetor caps, rear shocks, turn signals, instrument covers, and pullback handlebars; chrome exhaust with rakish, diagonal-cut mufflers. What isn't chrome is likely to be polished aluminum, like the headlight mounts, the instrument panel, the grab bar outlining the stepped seat, the cam cover, the fork sliders, the footpeg bases, the rear footpeg-and-muffler hangers, the engine covers.

If there's still any doubt, it's displaced by the tiny teardrop gas tank, the stubby tail section, the cut-back sidecovers and the fat, 16-in. rear wheel.

This is a cruiser. What about performance? Look at the horsepower and torque figures, 75 bhp at 9500 rpm, 36.5 lb.-ft. at 8000 rpm. Potent stuff for a 550 Four, and the reasons for that power output lie in the engine's genealogy.

Air-cooled, DOHC, link-plate cam chain, four valves per cylinder, offset rocker arms with hydraulic lash adjusters, plain bearing crankshaft, helical primary gears, hydraulic multi-plate wet clutch, six-speed transmission, shaft final drive. This is the smaller version of Honda's newest inline Four, introduced in the Nighthawk 650 and Nighthawk 550 for 1983. The engines share crankcase castings, clutch, transmission and cylinder head. The 572cc 550 has lower primary gearing and the same 60mm bore as the 650; stroke is shorter; 50.6mm to 58mm. To work with the 50.6mm stroke, the 550 has shorter connecting rods, crankshaft throws and cylinders. The crankshaft, designed for the 572cc version, is lighter with 1mm smaller diameter journals; the cases are machined to fit.

The engine is designed to be compact. It is narrow, the alternator mounted behind the cylinders, overdriven off the crankshaft by a link-plate chain. It is short, the transmission shafts staggered vertically instead of laying one behind the other.

It's also designed for low maintenance. The hydraulic lash adjuster automatically take up clearance between valve stems and rocker arms - meaning no valve adjustment is necessary - and pump down if the engine is over-revved, increasing clearance and reducing the chances of a mis-shift bending the valves. The transistorized electronic ignition is not adjustable, and has electronic advance. The hydraulic clutch, like hydraulic disc brakes, is self-adjusting.

Low maintenance doesn't mean low performance. The 550 has the same cams as the 650, and, used with the smaller engine, those cams are closer to the high-performance grinds sold by aftermarket engine builders than are most stock camshafts. The four Keihin CV carbs have oval throats, 26.8mm at the venturi, 30mm at the throttle plate, with lightweight throttle slides and thin diaphragms for instant throttle response. Combine the cams and the carbs with the lighter crankshaft and you've got a quick-revving, free-winding 550 that feels faster than anything in the class.

It feels fast because it has a big jump in horsepower and acceleration at 7000 rpm, gaining engine speed from there at an astonishing rate right up to the 10,000 rpm redline. It pulls well from 4000 rpm, well enough to leave lights quickly and have fun gaining speed, but then there's that kick at 7000 when the Nighthawk comes on the cams, and off it goes.

There's nothing to distract the rider from that magic rush of the tach needle toward redline, since the rubber-mounted engine is one of the smoothest ever put in a motorcycle. That glass-smoothness adds an eerie quality to the soaring tach and the kick-in-the-pants acceleration.

Slam the 550 into second gear at redline and the front wheel comes up and floats a foot or two off the ground, slowly settling as the bike continues to gain speed. Keep the Nighthawk near the redline, shifting quickly, and a rider on anything short of a sporting 1100 will have to work to keep up or pass. Street impressions send a strong message, that this is the most potent, quickest, fastest 550 around.

A trip to the dragstrip brought some surprises. ?The Honda Nighthawk isn't the fastest 550, with a best pass of 12.64 seconds and 102.27 mph. That's about as fast as a 1982 GPz550 and not as fast as a 1983 Suzuki GS550, even though the Nighthawk feels quicker than both.

The caveat here is that the Honda may be quicker than the Suzuki or the Kawasaki, or at least may have the potential to be quicker. The problem is that the 550's clutch is like other hydraulically-activated clutches - using a master and slave cylinder connected by an easy-to-route hydraulic hose - from Honda: grabby and imprecise. Add a grabby clutch and a peaky engine without the torque of say, a VF750F, and you've got a handful at the dragstrip. Ridden by the same rider, the Suzuki is quicker than (and the Kawasaki about the same as) the Honda. Both the Suzuki and the Kawasaki have cable-operated clutches with broad engagement points and easy-to-modulate release.

As for top speed, the 550 reached 116 mph in the running half mile, eight mph slower than the GS550.

That's as fast as the Nighthawk will go, since 116 mph equals 10,000 rpm (redline) in fifth gear. It won't go any faster in its extra-tall sixth gear (Honda calls it Overdrive), and it will only go that fast in sixth if the Honda is first run to the redline in fifth. Start accelerating at 60 mph I sixth and the Nighthawk struggles to top 100 mph under the best conditions.

What we have in the Nighthawk is a typical 550's five-speed transmission with an additional, taller cruising top gear added. Look at the GS550 - it's also geared for 116 in fifth (top), happily revs past redline to 124 mph in the half mile, and turns 5200 rpm at 60 mph. The Nighthawk's tall sixth gear, on the other hand, is made for highway cruising at a leisuerly pace, bringing engine rpm at 60 mph down to 4400 rpm from fifth gear's 5200 rpm.

Which makes it easy to understand why the Honda's top-gear acceleration times are much slower than the competition. The Nighthawk needs 6.6 seconds to accelerate from 40 to 60 mph in top gear (the GS550 takes 4.7 seconds) and 10.8 seconds to run from 60 to 80 mph in top (the GS 550 needs 5.6 seconds).

At 60 in sixth, the Nighthawk is relaxed on the highway, but accelerating quickly around slower traffic demands at least two downshifts, and headwinds or upgrades often require fifth gear. Cruising above 70 mph usually means spending more time in fifth than sixth gear, which, despite the 550 having a lower primary ratio than the 650 Nighthawk, is close to being too tall for the engine.

The carburetors, which work very well at most engine speeds, have a lean spot right at 4500-5000 rpm, the engine just a bit reluctant to pull, hesitating when the throttle is rolled on in that range. It takes full choke to get started in the morning, and at least half choke for a mile or two before the engine warms up, even in the summer.

That stylish, sleek gas tank makes the rider pay for its looks with a small, 3.2 gallon capacity. Under the best conditions, the tank holds enough fuel for 153 miles before reserve. Typical riding demands reserve after 120 or 130 miles, and the hardest open-road running saw the main tank sucked dry in just 73 miles!

The steel frame is conventional, built to be inexpensive, a single large backbone tube tied into the steering head with gusset plates, and twin downtubes cradling the engine. The steering stem uses ball bearings. The steel swing arm pivots on tapered roller bearings and uses tow shock absorbers, which have spring pre-load adjustments only. The leading-axle, air-adjustable front forks have a forged aluminum alloy brace between the sliders, and there's a single hydraulic disc brake. TRAC anti-dive is not used. Wheels are cast aluminum, a 2.15 x 19 inch front and a 3.00 x 16 inch rear, and the rear wheel houses a mechanical drum brake. The 550 is essentially a version of the 650. It is a little smaller, the wheelbase measuring 56.7 inches to the 650's 57.5 inches, thanks to a shorter swing arm. The 550 has 29 ° of rake (the 650 has 28.5°) and 4.2 inches of trail (the 650 has 3.9 inches). The 550 is lighter, 440 lb with a half tank of gas, compared with the 650's 465 lb with half a tank.

The 550's shorter swing arm has a couple of noteworthy effects. Because the rider and the engine are closer to the rear wheel, the 550 is more liable to wheelie under hard acceleration than the 650. Because the swing arm is shorter, stiffer shock springs and damping must be used to control jacking of the drive-shaft rear end under power, and the stiffer suspension is choppy over repetitive bumps.

The 550 has noticeable driveline snatch, especially at moderate speeds around town. The light carburetor diaphragms, which do so much for crisp, snappy response, are partially to blame here. The slightest movement of the twist grip has an immediate action at the carburetors, and any slack in the driveline is taken up instantly. There's a spring-loaded, ramp-and-cam damper built into the driveshaft. The damper helps isolate the transmission from road shocks but also contributes to the slop in the driveline.

Anybody taking the 550 farther than the corner grocery will find that the seat is hard enough to attract the rider's attention after 20 or 30 minutes. The seating position is much better than we've come to expect of cruisers, the relationship between the pullback bars, the forward footpegs and the stepped seat reasonably comfortable for most riders.

Despite being decked out as a cruiser, the 550's handling is as good as its engine. It is stable, turns easily, and has good cornering clearance - the footpegs touch first as an early warning system, and then only during the most spirited riding. Pushed beyond that, the 550 wallows slightly in sweepers with a 150-lb rider, the result of over-sprung, under-damped rear shocks.

Remember all those chromed and polished parts, such as the headlight and its brackets and the instrument panel? Ride the 550 east during late afternoon and all those polished parts reflect the sun into the rider's eye, producing a terrific glare and making it almost impossible to read the instruments. Under other conditions, the instruments are easy to read, although they are prone to outrageous optimism. The speedometer reads 60 mph at an actual 53 mph. All the usual lights are provided, the headlight doing a fine job of illuminating the road, the manually-canceling turn signal maintaining a constant tempo in the face of changing engine rpm. The choke control is on the left handlebar, right at the thumb's reach, rotating up and down. The control buttons, such as the one for the reasonably-loud horn, are chromed plastic, as are the screw-on covers for the fork air caps.

On the other hand, the helmet locks are nothing more than hooks under the seat. To secure a helmet the rider must remove the seat, slip the helmet's D-rings over a hook, and replace the seat. The battery must be removed from its niche under the airbox before water can be added, the air filter is hidden behind a cover secured by three screws, which is in turn hidden under the right-hand plastic sidecover.

On the plus side, the rear wheel axle clears the mufflers and removing the rear wheel isn't a major chore. And the Nighthawk's light steering, narrowness and engine response earned I several weeks duty as the commuter-of-choice for one man known to split lanes in bumper-to bumper freeway traffic.

This 550 Nighthawk, then, is a combination of glitter and glitz and solid function, providing a base of performance under all that style and chromed plastic. It's proof that motorcyclists can have it both ways, not giving up power for the cruiser look.

Source Cycle magazine