Nighthawk 650

Once upon a time, old-timers will tell you, a man and his machine had a special relationship. The man doctored and nursed the machine so that it might carry him. This symbiotic relationship only began with priming cups and long-armed kickstarters; the rider controlled ignition advance as well as throttle settings; at regular intervals the man would reach down and operate the manual oil pump; at regular intervals he would tend the chain, tighten the spokes and fix the latest flat. There was a time when a fancy engine-driven oil pump was seen as too appliance-like--too prissy for a real man and his machine.

Motorcycling has come a long, long way in 70 years. Now picture THE FUTURE MOTORCYCLE, a machine that takes care of itself, never intruding on riding time. Imagine this machine, a 650, quicker and faster than most 650s yet so smooth there is little difference between off and idle. Picture an almost no-maintenance engine in equally service-free running gear. Tune-up money you can invest now in money-market funds--or maybe an outrageous after-six caper.

Open your eyes and see that machine: Honda's CB650SC Nighthawk Any resemblance to last year's 40- inch Nighthawk is in name only. In 1982 Honda swept its Nighthawk styling over existing 450, 650 and 750 machines; none were mechanically new. The 1983 650, along with a similar 550, is an all-new motorcycle, and Honda's styling department redrew tighter, sleeker Nighthawk lines over the new foundation--only the Nighthawk emblems remain. The ideas manifest in the CB650SC might make a rider conclude that oil systems will soon re-refine themselves and spark plugs re-manufacture themselves, all while the engine is running.

The Nighthawk synthesizes ideas already proven in previous designs. Nothing is completely new, but no other motorcycle has incorporated all these no-and low-maintenance features. The CB650SC has hydraulic valve-lash adjusters and clutch actuation; self-setting cam chain and starter chain tensioners; and ignition, generator and drive systems that require no periodic servicing. Of course the no-maintenance concept trades today's troubles and expenses for tomorrow's. Nothing lasts forever, and when that shaft drive and those hydraulic adjusters need rebuilding or replacing, there'll be a price--a price merely postponed. Ride now, pay later.

But what a ride! No other 650--and few bikes of any displacement runs as smoothly, and no other 650 we've tested has had more power than the new CB. Its acceleration places it among 750 performers. Seating comfort, cornering clearance, handling stability and overall ride are all exemplary.

Honda designers condensed the engine's crankcase. Mounting the generator and starter behind the cylinders (like the Yamaha 550 and 650 Maxim and Seca series) narrowed the engine, as did stacking the transmission shafts and incorporating geared primary drive into a crankshaft flywheel. At 16 inches, the Honda's width across the crankshaft area is within a pencil thickness of Yamaha's 550. The Honda is 1.4 inches narrower than the Seca 650 and 3.8 inches trimmer than last year's CB650. Between the crankshaft and the transmission's output shaft, the Honda measures, front to back, 1.3 inches less than last year's 650 and 1.9 inches less than the Seca 650. This narrow engine can ride low in the chassis without impeding cornering clearance and can move forward to get more weight on the front wheel and allow for a longer drive shaft than would otherwise be possible. But the new 650 powerplant is quite tall; at 13 inches from crank centerline to the valve-cover top, it's just 0.8 inch shorter than the CB1100F.

Inside, five plain bearings support the forged, one-piece crankshaft. Sprockets at the center, between the second and third throws, drive the camshafts and generator with silent-type link-plate chains. Another sprocket between the third and fourth throws drives a trochoidal oil pump by way of a standard single- row chain. The crank has pork-chop flywheels except for the web next to the pump sprocket, the inside wheel of the fourth throw. This is a full-circle wheel machined into a 54-tooth primary drive gear. At the crank's far right-hand end lies the rotor for the magnetically triggered ignition.

Engine loads feed to a large, 92-tooth clutch-driven gear. A twin-gear, staggered-tooth primary drive minimizes noise and backlash. The wet, multi-plate clutch actuates hydraulically--exactly the way hydraulic brakes do. Squeezing the lever displaces fluid from the master cylinder through the hose, pushing a piston at the left of the engine; the piston moves a rod that runs through the main shaft to the clutch's pressure plate, which in turn separates the clutch plates.

The clutch lever has a very short engagement arc and hooks up rather suddenly; after about a dozen launches, however, the rider learns to compensate for the quick engagement. Shift action is crisp and smooth, with a short throw and very positive click-stops. Gearbox action is deluxe. Except for a relatively wide jump between fifth and sixth gears, the indirect-drive transmission is conventional. The long-legged sixth gear allows low rpm cruising without sacrificing acceleration. At 60 mph in sixth this 40-incher snoozes along at 3965 rpm, while fifth gear produces 4690 rpm-- just about the engine-to-road speed of other 650s.

Too-tall gearing usually means downshifting whenever the highway tips a few degrees uphill. Not so for this nightbird. The fierce little 650cc power-house churns out enough torque to pull easily up those long grades with a solo rider aboard. Packing a passenger and luggage may demand fifth gear if the grade is unusually steep, or if you want pass-at-once power. There's no driveline shock absorber anywhere within the engine's crank-cases. Instead, like the Sabre and Magna V-fours, the damper lies in the drive shaft, between the engine's output gears and the rear wheel's final drive gears. The secondary drive gears receive lubrication from the engine's oil system.

Upstairs, you'll find the piston and cylinder assemblies standard Honda issue. The three-ring, semi-slipper-type pistons, providing 9.5:1compression, attach to forged two-piece plain-bearing connecting rods. The four-valve combustion chambers have valves inclined 38 degrees to each other. The intake valves, 23mm in diameter, splay 18 degrees from the cylinder-bore centerline while the 19.5mm exhaust valves incline 20degrees. This four-valve cylinder head is a generation ahead of its CB750/900/1100 wide-angle counterparts.

Camshafts with mild profiles orchestrate valve action: duration, 225degrees; overlap, 15 degrees; lift, 7.5mm. Small tubes shaped like trombones spray the cams with a lubricating oil mist. These pipes also supply oil to small reservoirs for the valve-lash adjusters. Running the oil through these chambers separates the air bubbles from the oil before it's pumped into the hydraulic valve-lash adjusters, which require non-aerated oil.

The Honda 650's real sophistication shows in its automatic valve- lash adjusters. Harley-Davidson pioneered hydraulic lifters in its big overhead-valve twins 35 years ago, by putting the lifters at the bottom end of conventional pushrods. Honda has developed a system capable of functioning in a high-output, 10,000-rpm double- overhead camshaft engine. Most hydraulic lifter systems position the adjuster in the reciprocating valve train, and the entire lifter assembly rises and falls with the action of the cams. Honda anchors its adjusters in the cylinder head: the adjuster acts purely as a fulcrum for the lifter. This is important to a high-rpm engine because it avoids problems inherent in conventional systems, including increased reciprocating weight, pump-up, complicated valve-train harmonics and oil froth.

It makes no practical difference, hydraulically speaking, whether the lash adjuster is located between the cam and valve or employs a finger follower and then uses hydraulics to move the pivoting end of the finger follower up or down slightly. In Honda's system, a cam lobe bears against a finger follower, which pivots on one end and presses down on a valve pair at its other end. Anchored in the head, the hydraulic adjuster sits underthe follower's pivot; hydraulic pressure pushes up against the follower and eliminates the freeplay between the cam and the valve. It can't push hard enough to score parts or produce running clearances less than zero. The hydraulic system deals with clearance variations caused by operating temperatures and parts wear. You never touch the adjusters with a wrench. Neither must you attend to the four Keihin carburetors. The butterflies link together mechanically, and a special Hydrin rubber diaphragm operates the throttle slides. This material lasts longer than former types and responds fast enough to pressure changes in the overhead chambers that Honda engineers did not include accelerator pumps. The butterfly valve's diameter measures 32mm; the venturi area, where carburetor size is determined, is 29mm. Honda calls these units 32mm; technically they are 29mm.

At very low engine speeds, the bike's carburetion has a slight hesitation when the rider snaps open the throttle. Driveline lash and shaft reaction can at times amplify this glitch. After 4000 rpm power builds consistently until about 7500, where the 650 kicks in with authority.

Sandwiched between the carburetors, engine crankcases and cylinders is a compact and powerful AC generator. It features dual coils--one inner ring and one outer. The small-diameter rotor splits in two so that its finger-like magnets can be assembled on each end of the stator, with the magnets spinning between the inner and outer coils. The rotor spins 1.19 times engine speed, zapping out 280 watts.

Given its compact size and considerable output, the Honda generator needs forced-air cooling to control operating temperatures. A fan draws relatively cool air from the engine's left side, blows it across the coils, and thence out a duct at the engine's center. The starter motor, driving through reduction gears, turns a one-way clutch on the generator's shaft. This then spins the crank-driving silent chain which, like the cam chain, has its own self-adjusting tensioner.

The frame cradles the engine in a rubber mounting system that isolates vibration beautifully and so encourages the rider to rev this 650 well into its prime power range. A single, large-iameter backbone curves over the engine bay, joining the twin-tube cradle just above the swing arm at the rear engine mount. This is a rigid piece. The 19.8-inch-long swing arm, made possible by the compact engine, is among the longest in shaft-drive motorcycling.

Although a long arm can minimize drive-shaft torque reaction, the Nighthawk has enough up/down movement, especially in lower gears, to make its rider think the CB's arm is short. Sport riding produces shaft up-down reaction and also amplifies drive-line snatch. The rear suspension units, two VHD shocks, can't or don't control this throttle-induced up-and-down business very well. Despite having two-stage compression damping, four-position rebound damping and five spring-preload settings, the shocks still seem slightly over-sprung and under-damped. Sharp bumps or pavement breaks jolt lighter riders even with the spring preload dialed to soft. As for rebound damping, we rarely used the first two clicks; the damping force at those settings is just too limp. Run across a dip in a sweeper and the rear end pogos for a while.

Following current Honda practice, the 39mm fork operates without air-assist; air may be added to raise front-end ride height. The low-stiction fork produces a nice ride over all sorts of road surfaces. Damping seems just a tad soft, but we think a change to heavier-weight fork oil will cure this.

The cast wheels follow contemporary trends, with widths of 2.15 front and 3.00 rear. Dunlop's rubber, though a little hard for full-on sport riding, sticks well right down to peg-dragging. Riders compelled to grind metal in corners will have a tough time; the only pavement gnashing occurred crossing dips at very high speeds. This provocation caused the exhaust pipe shield to hit on the right and the centerstand tang to touch on the left.

At moderate speeds the Nighthawk's steering is nimble and light. At first we thought it might be a touch twitchy. As speeds increase, however, the bike's steering becomes slower and heavier, just the opposite of what's expected. At speeds approaching 80 mph, the CB650 steers slow compared to other 650s. Switching from fast right-to-left turns takes some effort and forethought.

Stopping power is excellent. The front brake has a light and progressive feeling, characteristic of Honda's twin piston calipers. This binder operates on new-style discs with flat-sectioned rotors. Honda controls the disc spacing from model to model by varying the width of the cast hub. The TRAC system minimizes front-end dive well; even under heavy braking there's some fork travel left for bump response. The single-leading-shoe rear brake uses one 30mm-wide shoe and one 40mm. It too offers good stopping power and sensitive feel.

Most riders will find the Nighthawk's seating position comfortable. Honda placed the seat's kick-up rearward enough to allow tall riders to stretch. Footpeg, seat and handlebar relationships accommodate short and tall riders for hours of comfortable riding. Some testers thought the bar too straight, needing a few more degrees of sweepback; others would prefer a slightly lower bar. Still, the 650 Nighthawk is a first-class compromise suiting a wide range of bodies. Nighthawk detailing has likewise benefited from experience on the road. Finger switches are well spaced--using bulky gloves poses no problem. A thumb-operated choke lever sits next to the left grip. The mirrors give clear images directly rearward. Both the rectangular quartz-halogen headlamp and the dual horns have long-range power. The centerstand tang gives good leverage, making the bike easy to hoist. The helmet lock easily holds two helmets, even those with short straps, without challenging the rider's dexterity. Like the engine, the chassis promises to deliver trouble-free daily operation.

The CB650 has a 12-month, unlimited-mileage warranty. About a dozen or so details must be inspected and serviced every few thousand miles. Anyone who can manage hand tools can perform most of these chores. For those who prefer to do their own servicing, here's a summary--a necessarily short one--of Honda's scheduled intervals: every 4000 miles, change oil and filter; every 8000 miles, replace spark plugs, clean the air filters and fuel strainer. There are also a few minor emission-related tasks. That's ll, except for a major servicing at 24,000 miles. Perform these services according to the Owner's Handbook and you'll keep the warranty valid; you don't need to have a Honda dealership's mechanic do the work.

Without doubt the new CB650's most impressive features are its valve-lash adjustment and its low-maintenance design. Honda engineers seemto have removed the last tedious, time-consuming ritual from motorcycling's Saturday afternoon.

Here is a machine that fulfills the 650 promise: it feels small, smaller than a 750, yet runs with 750s without even breathing hard. Its smoothness and comfort invite long rides. The rear suspension's springing and damping rates do need tuning to provide a more supple ride; and for sporting riders, Honda's engineering department should attend to the drive line's irksome lash and shaft reaction. Having a motorcycle that needs barely more maintenance than a safetypin is a bargain only if its owner genuinely enjoys the way the motorcycle works. Diehards may complain sourly about "appliance-like" character, but few riders will quarrel with the way this motorcycle functions. For about six or seven years, first one manufacturer and then another has proclaimed that its 650s perform like 750s; certainly there's been much sound to this proclamation but little real 750 fury. Now the 650 Nighthawk delivers.

Everyone who has ridden the 650 Nighthawk has come back impressed. This 650 is the new measuring standard of the 40-inch class. And the standard has just been raised. A lot.

Lose your Owner's Manual? CLICK HERE for a PDF version of the original Honda Nighthawk 650 Manual (1983 Model)