Honda CB 750SC Nighthawk

1982- In it's debut year, the 750 came in two colors; Candy Flair Blue and Cosmo Black Metallic. The tank and sidecover stripes were chrome with red pinstripes. Surprisingly, it came with an 85 mph speedometer!
1983- Only two changes were made in 1983; the speedometer was upped to 150 mph, and the colors were changed to Black, and Candy Wineberry Red. The black bike was adorned with a thick grey stripe bordered by white pinstripes, and the red bike had a black stripe bordered with white pinstripes.
The only Hondaline optional equipment available was Engine guards, body cover, and a handle-bar mounted quartz clock!

Road Test

Honda has dressed its tough transverse-four 750cc engine in cruiser clothes with a button-down one-piece look. The engine may be a veteran, but the motorcycle around it is as new as the latest in designer jeans.

In case you haven't noticed, motorcycle manufactures are doing battle on at least two fronts these days New Tech and Styling. Traditionally, the battleground has been New Tech, expensive though it may be. Styling, which as far as the Japanese were concerned began as an experimental end-run, developed quickly into mainline frontal attack. Bodywork costs less than totally new engines, but Styling, like New Tech, has its problems. In Styling, a company must observe the conventions of style, but not look like Me-Too. Which brings us to Honda's Nighthawk series: new bodywork, and in some places new flooring, on old foundations, like the 16-valve Honda 750; motorcycles built in the custom-special-limited fashion; and motorcycles in the 450, 650 and 750 displacement ranges that look distinctive in a cruiser world.

Case in point here is the Honda CB750SC Night-hawk. While it may not be New-Wave Tech, you'd be hard pressed to call a 16-valve four-cylinder motorcycle outdated and destined for the reprocessing crusher. The engineering department can keep updating the motorcycle with important innovations like Honda's TRAC (Torque Reactive Anti-Dive Control) system. Meanwhile, face-lifting and other cosmetic and structural surgery can give a showroom veteran a fresh image and new punch for the battlefield.

The 750 Honda engine has remained basically unchanged since its introduction in 1979. It does carry a new black finish with polished cylinder-head fins and a buffed-and-coated generator cover.This complements the Nighthawk look. The 4.5-gallon gas tank flows down to the side panels, along the seat's bottom edge, and into the duck-tail-style seat back. A cast-aluminum railing accents the seat, which seems cradled within the body. Frame color matches body color. Visually, the Nighthawk has a kind of one-piece integrity rather than a pieced-together anatomy.

Beyond the engine, nearly everything else is new.

Contact with terra firma is provided by Dunlop's tubeless Qualifiers, which wrap around new cast-aluminum-alloy rims  a first for Honda. While some Honda spokesmen say these wheels are the first ones that satisfied an engineering department concerned with porosity and therefore good airtightness, it's also clear that buyers prefer the cast-wheel look even though the Honda Comstar wheel is ex- of the Custom's geometry. The new fork cedent in design and in function. The measures 37mm, two millimeters up on SC's rim sizes are larger than the 750 the Custom. With the larger legs comes a Custom's: 2.50 x 18 front and 3.00 x 16 one millimeter increase in front axle off-rear, rather than 2.15 x 19 and 2.50 x 16, set, from 32 to 33mm. The frame's steer-respectively. The change puts more rub- ing head has been angled to accommo-ber on the pavement while providing a date the differences in fork and wheel way to get lighter steering. dimensions, bringing the SC's rake to Even though the frame and front sus- 29.5 degrees (like the Custom's) and trail pension are new, Honda engineers have to 120mm, close to the Custom's 117mm. manipulated the chassis to retain much The frame follows typical Honda 750 practice. A full double cradle surrounds the engine with an additional backbone tube supporting the well-braced steering-head area. The tube layout actually traces the F-model pattern more closely than the Custom's; large cast-aluminum brackets support the passenger pegs and the mufflers.

At the rear the SC's shocks are the same Variable Hydraulic Damping (VHD) components as the Custom's; however, the SC's top mounts are 30mm forward and 20mm lower; so the Nighthawk's shocks angle more acutely. A good thing. Compared with the Custom's ride, the Nighthawk's is quite cushy. Hard bumps deliver harsh jolts to the rider; smoother surfaces give an agreeable ride.

The fork, with its low-stiction compliance, is simply first-rate. While the wheel blurs over rough pavement, the fork isolates the rider from axle-level turmoil. The air-assisted fork uses Honda's dual Syntallic bushings, and a connecting tube links the legs so air-pressure adjustments can be made at one fitting. We found 11 to 14 psi about optimum for all-around use. Although more might give an extra measure of cornering clearance, the TRAC eliminates the need for seal-popping pressures to prevent nose-dive during braking.

Honda's Torque Reactive Anti-Dive Control system actuates differently than the Suzuki and Yamaha anti-dive front ends. Those setups use front brake hydraulic pressure to control a valve that closes the fork's compression-damping oilways, and they can have two drawbacks. First, additional brake-line plumbing and increased brake-lever ratios can produce a spongy feeling at the brake lever. Second, those systems are either on or off there's no modulation of anti-dive effect.

Instead of being triggered by a rise in brake-fluid pressure, Honda's TRAC activates mechanicallyindependent of brake-system hydraulics—through the torque reaction of the brake caliper. The Nighthawk's left-hand brake caliper hinges behind the fork leg on a pivoting link. When the pads grip the disc surface, the disc tries to drag the caliper around with it. The caliper pivots, pressing against the anti-dive mechanism's activating valve and closing off the fork's compression-damping oil passage. This valve, in the shape of a piston, is normally held open by a spring. In a very simple non-TRAC system, applying the front brake would cause a valve to close and increase compression damping, which would reduce front-end "dive."

TRAC is more elaborate. Forward weight transfer during braking compresses the fork, raising fork oil pressure against the underside of the TRAC activating valve and, through the valve, pushing against the caliper's braking torque. These two opposing forces  fork-oil pressure and braking torque interact through the valve to provide progressive anti-dive. Hitting a bump causes a sharp pressure rise in the fork. This rise can cause the valve to push hard enough against the opposing force of the caliper to open, partially or fully, the normal compression-damping passageway. This opening allows the fork to respond to a bump. Moreover, TRAC's design provides a constant modulation between fork anti-dive and bump response.

Not everyone wants or likes a single anti-dive setting. A rider can dial in the SC's anti-dive effect with a four-position adjustment on the left-hand fork leg. The adjuster controls a small secondary oil-way parallel to the main compression-damping passageway. This secondary passage provides a way to bleed-off fork-oil pressure from under the anti-dive valve. The rates at which this bleed-off occurs are controlled by orifices, the size of which can be controlled by an external adjuster. Position one corresponds to the largest orifice, which offers the least resistance to the passage of fork compression-damping oil; positions two and three expose progressively smaller, more restrictive orifices, increasing fork damping pressure. The fourth position exposes no hole; all fork-oil pressure comes to bear on the valve's underside and against the braking torque.

Normally, a fork has much lighter compression damping (one-fourth) than rebound damping. In the TRAC system, when the anti-dive seals off the main compression-damping passageway, compression damping becomes two or three times stiffer than normal when the adjuster is set on position one. On successive settings the compression-to-rebound damping ratios become increasingly biased toward compression.

So much for theory. How is it on the road? There is little feeling of anti-dive effect when the adjustable orifice is set on position one; the fork compresses much like a conventional fork under hard braking, but there's some travel available for bump response. On position two the fork resists the front-end braking dive, and the fork's bump response is firmer. The difference is small but obvious. Position three gives a noticeably larger increase in anti-dive effect, producing firmer resistance to front-end squat from braking and stiffened reaction to bumps. The fork still dips when the brakes are applied, but slower; it still responds to bumps, but it delivers a firmer jolt. Position four produces more substantial effect in the same direction.

Riders who use their front brakes without any particular vigor will find the first two positions useful. These allow the fork to respond nicely to bumps during braking while giving a wonderfully smooth cruising ride. Our staff testers preferred position three for rush-about riding. It provides a measure of squat-resistance and yet responds nicely to most surface whoops. Those who stand their motorcycles on headlamps during braking will like the fourth setting. It gives generous resistance to front-end sink, yet responds to hard bumps.

Those who brake heavily while cornering hard will also appreciate the Night-hawk's wide wheel rims, large-section tires and excellent dual-piston brake calipers. Few riders brake while dragging the footrests, but those who do can use TRAC to advantage when scrubbing speed entering a corner without worrying about front-end dive robbing cornering clearance.

The dual front disc brakes use Honda's excellent dual-piston calipers. The compact, dual-piston design puts more brake-pad area on a narrower band around the rotor perimeter. This accomplishes two things: First, it increases the calipers' braking leverage by moving the pads slightly farther out, making it possible to whittle away more rotor surface to reduce unsprung weight. Furthermore, the smaller caliper castings resist deflection the "opening clamshell" effect under heavy braking, which helps eliminate the rubbery feeling at the brake lever. Also, the smaller pad area more easily clears water off the rotor during wet-weather braking.

All this theory translates to consistent, powerful and controllable braking under a variety of conditions. In downpours it takes just an instant to return normal stopping power to water-saturated brakes. And stopping power is good. Even more important, though, feel at the lever is positive. The rear brake, a drum-type unit, may seem less performance-oriented than a disc brake; in fact it delivers outstanding performance, with strong stopping power and good feedback.

Riders who take their motorcycling in small doses will see little compromise in the Nighthawk's seating position. Beyond the 40-minute mark, the swept-back handlebar cramps the rider's seating area. Worse, the angle at which the bar sweeps back puts wrists at a cramp-up angle. Without exception, every tester got wrist fatigue, and then pain. Everyone who rode the Nighthawk complained of the bar's grip angle. The bar also forces the rider back against the seat hump; and when riding into a headwind or at high speeds, the rider must pull into the bar, straining both arm and back muscles. Tall testers found the seating tight but reasonable for short trips.

The frame rethink and redo didn't solve, even partially, the Honda 16-valve 750's most annoying characteristic: buzzing engine vibration that becomes apparent almost at once, though it's fatiguing only after many miles. The buzzing can be felt in the handlebar, tank and seat at engine speeds above 4900 rpm. While a mild, non-irritating vibration appears in the solid-mounted footrests at nearly all speeds, the other components tingle at a noticeable level between 55 and 70 mph. Noise is another consideration. The engine turns 4400 rpm at 60 mph, which isn't much; however, some riders may find the mechanical busyness a little wearing.

The same 16-valve powerplant that propels the Nighthawk also powers the Custom, the economy K-model and the sporting F-model. Our test bike produced 65.57 horsepower on our dyno at 9000 rpm, compared with the 69.50 horsepower at 9500 rpm of the 1980 CB750F we tested in December 1980. The F-bike Honda delivers more thrust due mainly to its more efficient four-into-two exhaust plumbing.

In major features the current 750 follows the dominant norm for Japanese engine architecture. Twin camshafts operate directly on bucket-and-shim followers. Light and efficient, this system has no screw-type adjusters, although valve-lash adjustment is rather complicated and time-consuming. Although the 63-degree included valve angle is getting dated, the engine puts out good power with crisp response. The power kicks in with an assertive tug above 7000 rpm.

The one-piece crankshaft spins on five plain bearings. A Hy-Vo chain carries off the power to a jackshaft and thence to a primary gearset, clutch and transmission. The clutch engages a straightforward indirect-drive gearbox.

Hot or cold, the engine starts instantly even when ambient temperatures approach freezing. The clutch-lever-mounted choke control is convenient and makes modulating the choke a hand-on-the-grip task. The clutch has light pull and an easily controlled engagement point, but the engagement arc is Way Out There; small hands must stretch to reach it. Other controls and switches are fingertip accessible with exception of the triggering right-hand turn signals. Because of the awkWard angle of the handlebar, the rider's left hand must be cocked at a peculiar angle to manipulate the switch.

Shift-lever action has a nice, mechanical feeling; however, our test bike had the same shifting flaw we've experienced with other 750-series test bikes. Occasional false neutrals appeared, especially when shifting to fourth, up or down. Careful attention to shift-lever movement produces fewer missed.shifts, but this tendency toward missed shifts is characteristic of the 16-valve Honda CB-bikes.

The tough and easily maintained engine has a forward-jutting magazine for a disposable paper-type oil filter. It makes changing the 4.7-quart oil supply a simple task. The all-electronic ignition is magnetically triggered and electronically controlled. No points, no governor weights and springs, no adjustments. The battery is accessible through the right-side panel. Besides the shim-type valve adjustment, the only real hassle is the air cleaner, which can be found only after removing the seat (two bolts) and the fuel tank (one bolt and pull the gas line).

That Nighthawk-look doesn't come free: if you want to load some luggage for an overnight trip, you'll be challenged by the missing bungee attachment points; the non-flip, bolted-on seat is incompatible with instant tank-bag installation; and if you hook bungees to the cast-aluminum accent piece the hook-ends scratch the side curtain's paint. After trying to rig a load you'll believe the Night-hawk is better suited to the role of Interceptor than Transporter.