Honda CB 400T Hawk II

Cycle World Road Test 1980

IN THE LIFE-CYCLE OF MOTORCYCLE models, there's much to be said for early retirement. Motorcycles with secure niches and no direct competitors can survive for a long time, but in a highly competitive market, senior citizens wobble off with black eyes. That's what happened to Honda in the so-called 400cc four-stroke market in the early 1970s. Honda had a perfectly nice (for 1973) CB360, the pedigree of which traced back to 1967. But by 1976 the poor old dear was getting roughed up in the sales derby by newer four-stroke twins from Kawasaki, Suzuki and Yamaha—which had either more displacement, better handling, smoother running counterbalanced engines, or all of the above.

Honda pensioned off the battered CB360 in 1977, and rolled out the totally new CB400 to deal with, rather than reel from, the competition. The CB400 featured three valves per cylinder, counterbalancers, composite wheels, new-wave suspension and a rigid chassis. The new 400 proved quick in the quarter-mile for a four-stroke 24-incher; it was reasonably comfortable and handled a good trick if you can pull it off. Honda thinks so too, and has enough
magic to make the trick work.

very well indeed. Honda could give black eyes as well as receive them.
Honda's changes for 1980 resemble the back-and-forth horsetrading that takes place in SALT negotiations: one for them (EPA) and one for us. Big Brother's tighter 1980 air pollution standards prompted Honda to downsize the carburetors, switching from 32mm CV Keihins to 30mm units. One for them.

Honda added a common accelerator pump for the two Keihins to maintain sharp throttle response despite the leanish slow-speed and mid-range circuitry. One for us. And so the trade-offs go. In our test bike, the smaller carbs dropped the horsepower and torque curves from the 1977 levels. But a new six-speed close-ratio transmission keeps the 1980 engine working higher in its powerband and putting more area under the curve when the engine is really twisted. Consequently, the 1980 model can trim over half a second off the quarter-mile time of the comparable 1977 version. Honda saved weight by deleting the kickstarter apparatus, but gained it back in swoopy new body styling, keeping the old and new just about equal at 403 pounds. In the final balance, the Hawk ends up well on the plus side; it still has a few drawbacks but enough improvements have kept it a very balanced middleweight.

The 400T engine still boasts state-of-the-art engineering. Three valves per cylinder are actuated by a single overhead cam, with two 26mm intake valves and a single 32mm exhaust valve. Two intake valves allow more air/fuel mixture into the cylinder than would be possible with a single intake valve. Although two valves may not provide anymore valve area than one large valve, two valves will produce greater flow, in part because two small valves have greater total circumference than one larger valve, and the air flow, especially at low and partial lift, takes place right along the edge of the valves. Lighter valves can also be persuaded to follow more aggressive cam lobes than one heavy valve; consequently, these more flow-effective valves can be opened and closed more quickly, and this provides more time to move the air/fuel mixture into the cylinder.

This unusual valve arrangement forms an integral part of Honda's "Pentroof" head shape which has been refined for 1980. The combustion chamber covers a large hole in the cylinder—the bore is 70.5mm, and that big piston only runs through a 50.6mm stroke. By way of comparison, the old GS400 Suzuki dimensions were 65mm x 60mm. With such an expansive combustion chamber, Honda has gone to great pains to gather in the air/fuel charge, directing and compressing it into one compact area squarely atop the piston to maximize the work done by the combustion chamber burning.
In this area Honda has made the most interesting series of changes to their Pentroof combustion chamber and piston. The piston is now flatter and its outer perimeter has a very gentle dome-shape leading up to the plateau area above the valve cut-outs.

The combustion chamber has been reshaped and dropped down to conform closely to the terrain of the piston top. The combustion chamber drops so low at two points that the piston must have two small divots to provide sufficient clearance.

The previous CB400 had a somewhat vertical stop in its piston top just a few millimeters away from the cylinder wall and a less compact combustion area. There are underside differences between old and new too. While both pistons are slipper types, the new piston has had each thrust face strengthened by the addition of a rib cast into the interior of the thrust face.
The 1980 version has stronger pistons; but, then again, it revs higher. Even though the Honda 400's horsepower peaks now at 9000 rpm (instead of 1977's 9500 rpm) the tachometer redline reads 10,000 rpm (instead of 1977's 9500 rpm) presumably to encourage the rider to make full use of the close-ratio six-speed gearbox and extract maximum performance from the 400. The short stroke keeps the piston speed down to a modest 3333 feet per minute at 10,000 rpm, and the pistons ride on connecting rods which turn a one-piece forged crankshaft. The crank spins in plain bearings and the 400's high pressure trochoidal oil pump keeps the bearings supplied with the necessary volume of oil.

While high-rpm durability should be good, high-rpm usability is another matter. At highway speeds ranging from 50 to 70 mph, the Hawk produces mild vibration, sending just a tingle through the handlebar and pegs. About the same amount of vibration can be detected in the passenger pegs as in the rider's, indicating that vibration is well controlled rather than just being hidden by a set of trick foot pegs.

The vibration isn't really bothersome; it's just enough to remind you that you're riding a bike, not a Cadillac. However, once the engine hits the powerband at 7500 rpm, the shakes start in earnest, with quite a buzz coming through the bar, seat and pegs. The Honda counterbalancer system should take care of the pulsing which comes from the 360-degree twin that runs the pistons up and down together. A 360-twin acts just like a single; it vibrates due to considerable primary imbalances.

The 400 has two counterbalancers, driven by a common chain off a crankshaft sprocket that lies between the flywheels.
One balancer shaft is in front of the crankshaft, the other behind, and they turn in the opposite direction of the crankshaft. Though Honda has taken elaborate measures to incorporate these chain-driven balancers, the CB400 engines have never been as smooth as the 180-degree GS400 and GS425 Suzukis, which have gear-driven counter-balancers.

That's not evidence that the Honda system isn't as effective as a counter-balancer unit per se; other features of the Honda engine may make it more difficult for any counterbalancer system to work.

This much is certain. The Honda is much smoother than the Yamaha XS400, which has no counterbalancer, but the Hawk can't match the 400cc-family of Suzuki twins in engine smoothness.
With the '80 CB400T, kick starting becomes outmoded and impossible. Honda felt the starting system and charging offered sufficient reliability in the Hawk. A blanked-off hole on the right side is all that's left. Forgetful types inclined to leaving the ignition on will have to resort to the even older bump-start method, but Honda owners get an edge here.

The Hawk and CX500 share similar Tri-Pulser Capacitor Discharge Ignition systems which dispense with breaker points. But in addition, these CDI systems are magnetoenergized and therefore generate their own spark, making the push-start job (if necessary) much easier.
Cold-starting the Honda posed no problems as long as the handlebar-mounted choke knob was put to use. In addition, the Hawk could be ridden while choked, quite an advantage since it takes so long to warm up. Warm-up periods are frustratingly long, but premature departure is punished with a series of sputters, coughs and gags unless the choke is left on.

Once warm and underway, the carbs work fairly well. Thanks to the common accelerator pump, lean carburetion staggers induced by quick openings from part throttle are eliminated. This is important, since fixed jets and needles make recalibrating a thing of the past. Honda does offer a high-altitude kit to lean out mixture in mountainous locales, but no sea-level enriching kits are available. Honda has also managed to tame the dreaded slamming-slide malady, that CV characteristic that abruptly drops the slides when you nick back the throttle and causes the motorcycle to slow down with a lurch. CV carbs rely on the differential between atmospheric pressure and inlet tract pressure to cause the slides to rise and fall. Honda's CVs work well, providing more margin of erIt
A diaphragm-type accelerator pump feeds both carbs. Keihin CV 30mm carbs come with accelera.
ror for throttle control inexperience, yet costing little in engine response.

The smaller carbs and lean settings do manage to work very well as far as gas consumption is concerned. After 100 miles of back-road thrashing, the '80 Hawk still returned 43.6 mpg, better than the average for 1977. This year's average worked out to 52.0 mpg and a careful highway cruise produced a conservatio

n-conscious 62.7 mpg. At this rate a Hawk tourer could cover 177 miles before calling on reserves.
Although carburetion characteristics have improved, driveline snatch plagues the Hawk. While in sixth gear and on the center-stand, the rear wheel can be turned freely 20 degrees before all the driveline lash is taken up. This lash or dead space causes jerks and lurches when the throttle is rolled back and then opened again. In stop-and-go traffic this bucking becomes annoying, although it's less aggravating in freeway situations. The lurch also becomes disconcerting if circumstances happen to put you on trailing throttle in a corner.

A sixth gear (introduced in 1979) keeps first gear at its original overall ratio (19.76); all cogs are spaced closer together; sixth gear (6.73) is just a bit taller than the original fifth gear (7.77). A half-dozen ratios feel like too many around town, allowing the rider a choice between three cogs. At the drag strip, however, the closer-set ratios produce a remarkable edge; although our 1980 Hawk's 34.16 peak was down 1.42 horsepower on 1977's version and was two pounds heavier, the '80 model turned a 14.33-second quarter-mile, making it six-tenths quicker than its Hawk II predecessor and presently the quickest four-stroke twin in what's left of the 400cc class.

Last year the Yamaha XS400 (November 1979) turned in a 14.76-second quarter-mile and the now-superceded GS425 (June 1979) stopped the drag strip clocks in 14.54 seconds.
Honda engineers used exhaust tuning to carefully shape the powerband for more mid-range power. They reportedly tested over 30 exhaust systems before arriving at their '' Power Chamber'' exhaust system. A heavy steel collector, designed to fit tightly underneath the engine, muffles, then splits each power pulse through two chromed mufflers to further silence the exhaust note. More than just a dumping box, the intricate Power Chamber contains overlapping, curved exhaust pipes which form an indirect exhaust gas path.

The pipe also has a pattern of holes at the bend which purportedly provides a more direct path for the high-velocity gases at high rpm levels, thereby reducing excessive backpressure. Honda's test results show a definite gain in midrange power over conventional two-into-two systems, with a very small loss in top-end power past the peak. Given the Hawk's delicate carburetion and the difficulties of remetering the carbs, discarding the stock system (legal questions aside) would very likely lead to severe driveability problems and a loss of horsepower. When you're dealing with 30-odd horsepower, manufacturers are already doing a remarkable balancing-act between emissions, power and driveability.
A slick gearbox and fat powerband on lesser bikes could be major selling points. With the CB400T, they only complement one of the best handling motorcycles available today.

The Honda 400's steering geometry provides light, precise and responsive steering, yet the bike is not overly sensitive to the
rider's every twitch or wiggle. The steering geometry figures remain the same: wheel-base 55.6 inches, rake 27 degrees and trail 100mm (3.9 inches). But these numbers alone don't automatically produce a handling champ—the Honda must blend good geometry with other solid features to emerge a winner.

Some of the credit for fine handling must go to a 400-class bike's standard features rather than Honda's engineers. First of all, a 400cc engine just doesn't make enough horsepower to tweak the frame out of alignment. Shoe-horning seventy ponies into the Hawk chassis might produce many handling changes, probably bad. Also, the CB400T weighs in at a currently modest 403 pounds, not enough to overwhelm the suspension components. The fork and shocks rebound-damp well enough to prevent wallowing or oscillation in most cornering situations, including fast, bumpy roads. Fork and shock spring rates suited our 160-180-pound test riders, though the feel leaned more toward

Source Cycle World 1980