Saturday, January 3, 2015

From Super Hawk to Black Bomber

Following the wild success of small Honda motorbikes during the 60’s, many riders moved to larger models from the Japanese manufacturer and specialist at producing reliable and complex motorcycles. There were the 125s and the 150s, but the larger family of 250cc and 305cc bikes were the big boys from the Japanese company.

These bigger bikes were divided into three types, Dreams, Scramblers, and Hawks. The Dreams were considered, at least by Honda, as touring machines. With their unusual pressed steel frames and complicated, leading link front suspension, they had a little bit of motor scooter in their DNA from the flared fenders to the fully enclosed headlight nacelle. The 16 inch wheels on the Dream made them closer to the ground than either the Scrambler which had 19 inch and the Hawk with 18 inch wheels.

The Scramblers and the Hawks were more like traditional motorcycles with their tubular steel frames and telescoping front forks. They did share a lot with the Dreams, however.

One item Hawks shared with Dreams was the fact that the engine replaced part of the frame. The usual down tube in the front of the frame was eliminated by bolting to the top and bottom of the engine. The thirty degree forward cylinder angle not only lowered the overall motorcycle height, but also made this frame design practical and possible.

Only Scramblers had complete frames with a vertical down tube in front of the engine. They also added a skid plate and reinforced handle bars as well as high pipes to complete the off-road package. In addition, at 52.4 inches, the Scramblers had the longest wheel base of the three models. Super Hawks had the shortest wheelbase at an even 51 inches.

These Hondas all had two-cylinder engines with the pistons moving in the same plane, a design usually called “twins.” The light weight aluminum engine had a single overhead cam driven by a chain with a manual tensioner mechanism. The short connection from camshaft to valves allowed for very high RPMs compared to push rod designs from American and British manufacturers. The engines were slightly over-square with a 60mm bore and a 54mm stroke.

All together a very advanced design built with great precision and care. The net result was that these relatively small, 250-305cc engines were strong competitors against motorcycles with twice or more displacement. Another result was a very reliable engine with minimum maintenance requirements. There was less vibration and shaking in these designs. These features became readily obvious when you hopped on a Honda and rode.

They all had four-speed transmissions and a multi-disc, wet plate clutch. Primary drive was a single row chain as was the secondary. Drum brakes all around with twin-leading-shoe on the front and a single-leading-shoe on the rear. Pretty typical for that era whether from a Japanese manufacturer or any other motorcycle built in America or Britain.

All three larger motorcycle types produced by Honda shared the same basic model of power plant. They looked pretty much identical from the outside with their wide cylinder head making the top of the engine look larger. However, internally and out of sight, the Hawks did one thing decidedly different. While the Dreams had what is called a 360° timing, the Hawks had 180°, a crankshaft layout shared by the Scrambler line.

These angles are a reference to the relationship between the two pistons in these twin-piston engines and the four-stroke cycle. A four stroke engine goes through four cycles in its up and down motion: 1) power (down), 2) exhaust (up), 3) intake (down), and 4) compression (up). Therefore, each cylinder only fires once every two revolutions of the crankshaft and flywheel assembly. There are 720 degrees in a complete four-stroke cycle. (This part is true of all four-stroke engines, regardless of manufacturer.)

A 360° engine has the pistons running together, up at the same time and down at the same time; but the cylinders alternate their ignition. When one piston is firing and being pushed down by the force of the expanding gasses, the second piston is coming down on the intake stroke pulled by the crankshaft. This balances the timing of the firing equally from the left side to the right side and back to left. Sort of 1 - 2 - 3 - 4.

This balances out the power impulses and makes it feasible to use a single carburetor for both cylinders, simplifying design and tuning as well as lowering complexity and cost.

The Hawks, on the other hand, with 180° timing, have pistons in opposition. That is, when one is up, the other is down. This causes the firing to occur on a non-symmetrical “fire, fire, intake, intake” strokes. Sort of 1 - 2 - 3 - 4 with the emphasis on 1 and 2 instead of 1 and 3. Having one piston traveling down while the other piston travels up balances out the vertical forces from Newton’s laws, but now the impulses aren't balanced and dual carbs are required for each cylinder to breathe equally.

The different timing produced the unique exhaust sound particular to the Hawks, but also created a complex rocking force on the crankshaft. Honda engines, unlike most their competition, used three main bearings on the crankshaft, so the rocking force was well handled. However the twist or torsional forces on the crankshaft were not balanced. Still, with such small pistons, the vibrational forces were relatively small in both designs, although a distinct buzz could be felt in the handlebars, especially at high rpm.

(Typical of most four-stroke engines, the predominant vibration mode is at twice the rpm. Hence the buzz feeling. The very high rpm capability of these engines raises the frequency of the vibrations.)

There were other differences in the Hawk’s engines that improved performance including a higher compression ratio than the Dream engine (10:1 vs. 8.2:1) and cam timing, as well as the dual carburetors. Higher engine red-line make the Hawks good performers. Capable of 9,000 rpm, it could propel the bike at over 100 mph; as fast as British parallel twins with much higher displacements, and with surprising reliability for such a complex design. Nine thousand rpm was not the norm for motorcycles of this period, and was one factor in putting this relatively small size engine in the same class as larger twins from Great Britain. While the Dream 305 produced 24 hp at 8,000 rpm, the Super Hawk hit 28 at 9,000. Doesn’t seem like that much difference, but the 305 Dream weighted in at 372, the Super Hawk was 21 pounds lighter, yielding a top speed of 104.6 according to a Cycle World review in the May ’62 issue.

The Super Hawk is now regarded as the first modern Japanese motorcycle that established the paradigm that we still operate under now, more than fifty years later. Perhaps you did meet the nicest people on a Honda … a 50cc motorbike, but those you met on these hot rods were not just the nicest, but some of the fastest too.

Although you could argue that Honda built a 250cc model to meet certain racing categories, in the US, the 305cc was the most popular model by far. The 305cc CB77 was called a Super Hawk, with the extra superlative an indication of the slightly larger displacement.

The Super Hawk's design is not an accident by any means. In saying "design," I don't isolate pure function — the bike's mechanical prowess — from its other aspects. One need only to take a good look at this model in order to sense that the aesthetic quality is inseparable and, perhaps, paramount in securing the Super Hawk's place in motorcycle history. (Check out the large photographs included at the bottom of this article to make your own determination of "style.")

If you are not convinced, consider what Soichiro Honda — Mr. Honda, himself — had to say on the subject of design and, in particular, on how design relates to his motorcycles. This shows that Honda's boss and leading racing proponent was also interested in how a motorcycle looked in addition to its performance and reliability.

I mentioned a little while ago that design is fashion. What I meant was the psychology of fashion that is the mental process that takes place among consumers when they see somebody doing a different thing, they also want to do so.

Balance is important for design, yet if balance is over emphasized the result might be a withered one. There is a contradiction between [the passiveness] and the strength of beauty, accompanied by a single direction. This is the hard point.

At any rate, the design of the motor vehicle must be a symphony appreciated visually. As the symphony would be unbalanced by only a single unordinary tone of the trombone, the design must be considered one by one without breaking the balance, such as tires, steering handle, and others. Moreover, each part within the balance has to express its respective unique design. This is of the most importance.

Soichiro Honda
December, 1961

This Super Hawk was the top performing motorcycle that Honda produced from 1961 to 1965. It was a very popular bike with riders back then as well as vintage restorers now. The list of famous Super Hawk riders includes the bike Robert Pirsig rode in his compelling road story, Zen and the Art of Motorcycle Maintenance; and — although they held a fondness for Triumphs — Steve McQueen and Clint Eastwood rode Super Hawks too. Even Henry Winkler — The Fonz — was photographed on a Hawk.

The engine design was based on Honda’s experience in Grand Prix racing in Europe, but it was still a rather mild copy of the exotic race bike gracing the European tracks. Somewhat quietly, in 1965, Honda went a step larger with their 450cc twin design. This machine, the CB450, was the first instance of a production motorcycle with dual overhead cams. The 450 moved the cylinders to a vertical position and added a downtube, releasing the engine from the requirement to be part of the frame. The most radical feature was the valve springing. Instead of the conventional coil springs, it used “torsion bars” — rods of steel that twisted to provide the spring effect.

While the Super Hawk was quite quick for its size and able to run with many of the British 650s, the CB450 pushed the performance envelope even further and reinforced Honda's reputation as a manufacturer of technically innovative and sophisticated motorcycles.

This largest yet power plant offering yielded 43 bhp at 8,500 rpm with a weight of 425 pounds. Cycle World Magazine tests in September of 1965 reported just over a ton at 102mph and a 15.2 second quarter mile. Like the Hawk it had a 180° crank and dual carburetors. The carbs were constant velocity design, new for that time period, but destined to become more common on newer bikes of all brands. It had the same 18 inch wheels as the 305 Super Hawk, but had a seat height of 31.5 inches, one and one-half an inch taller. The slight incline of the Super Hawk cylinders allowed for a bit lower seat height.

Although Honda didn’t use the name, the first CB450s quickly earned the nickname of “Black Bomber.” (In Canada, the model was referred to as the "Hellcat.") CB77 Super Hawks could be had in black, blue, red, and even white. The CB450 was only manufactured in black or blue at the beginning. The first year’s model, called the K0 in recognition of Honda’s nomenclature, had the same high humped gas tank as the Super Hawk. That led some commentators to dislike the overall style, although I had no problem with it. The new DOHC bike also shared the oval shaped, combination speedo and tach that was emblematic of the Super Hawk.

There is a style issue on the K0, however, that I don’t like. The side covers are a wrap around the air filter and typically painted a light, contrasting color that drew attention to what were not very attractive pieces of metal. To make things worse, they carried a large label that not only indicated “450” but also listed the Air Cleaner maintenance schedule in miles and kilometers. Not cool.

Model Years and Honda K Numbers

One of the confusing things about early Hondas is the question of what year any given model was. Honda was not using annual model-year changes when the first bikes were imported to the US. Changes and improvements were made on a running basis with no holding back until the next year. When significant changes were made, the different models variations were sometimes referred to as the "early" model and the "late" model. This is true of the Dreams and Hawks produced in the sixties. Because of this, it is sometimes difficult to determine a specific year of manufacture for early Hondas.

This system of running changes was used up until 1968, when the K numbering convention was introduced. Basically, the first version of a model was the K0 with subsequent model variations being assigned sequential K numbers: K1, K2, and so on.

In September of 1973, beginning with the 1974 model year, Honda adopted an official model-year policy. Even so, the K number designations were used through 1976.

The 444cc twin was a running portfolio of Honda’s engineering capacity. Four caged roller bearings supported the crankshaft, and primary drive was by spur gears. The valves were seated by torsion bar valve springs — short lengths of steel splined into tubular guides. Tight valve clearances and effective mufflers aided quiet running. The 450 also boasted a pair of 36mm constant velocity carburetors, a first on a production motorcycle. It shared the basic clutch design and front and rear brake specifications with the earlier Super Hawk.

Honda claimed the short stroke engine would develop 43 horsepower at the crankshaft and could reach 112mph. Cycle World recorded a top speed of 102mph in its August 1965 review. In contrast with most other bikes of the time, which pulled strongest at lower rpms, Honda’s 450 produced its best power at over 6,000 rpm. Reliability was excellent, provided you remembered to warm up the engine and changed the oil regularly — the service manual suggested 1,500-mile intervals. The horizontally split cases didn’t leak, and the electric starter always worked, hot or cold.

Contemporary testers noted several faults, including poor rear shocks, vibration, and the aforementioned need for a longish warm up to ensure a sufficient supply of oil to the top end. Over-revving the bike when cold could cause premature engine failure. Some also noted the bike’s oddly spaced gear ratios and the lack of a 5-speed transmission, a feature that would finally come a year later. And at a dry weight of 412 pounds, the K0 was heavier than a contemporary Triumph 650, which weighed in around 365 pounds dry.

These technical issues, later to be resolved, set aside, the Black Bomber pushed the performance envelope beyond its predecessor Super Hawk and firmly established Honda as a leading producer of advanced technology and high performance motorcycles. However, the bike never achieved great market success, and it would have to wait for its descendent, the Honda CB750 Four and the following Gold Wing designs to truly cement Honda as the greatest motorcycle technology company of all time; a reputation that has also spilled over to the Honda motor car products. It is a reputation of performance, innovation, and reliability that was honestly earned by such products as the CB77 and the CB450.

In February 1968, the K0 was superseded by the K1, with a 5-speed gearbox, a more conventionally shaped tank, a larger oil pump to aid warm up, and a longer wheelbase to improve handling. After the introduction of the CB750 Four in late 1968, the 450 twin was no longer Honda’s flagship, but continued through 1974 in an important role as a middle-weight street machine.

Not only did the K1 changed the fuel tank shape, but they replaced that ugly air filter cover with regular, bulbous side panels. These panels had a large, cast metal insignia with the numbers “450” prominent. Later versions changed the metal logo to add the initials “DOHC” to the displacement numbers, celebrating the unique valve design.

Since both the K0 and the K1 models had chrome side panels on the gas tank, they were an obvious transition from the matching Super Hawk design which was discontinued in 1967. (Check the pictures below which put the Black Bomber under the Super Hawk for comparison.) Vintage collectors prefer these first two models to the later designs because of the unique look. Personally, I like the K1 best because it maintains the Super Hawk styling but improved motor and transmission. The best of both worlds, although it still lacks a disc brake.

Honda changed the style again in the 1969 K2 CB450. The tank took on a new form and style, eliminating the chrome side panels and plastic emblem badges for a striped paint look that became the common design motif for Honda motorcycles through the seventies. It was in ’69 that Honda produced the first CB750 with this same new tank style. This new model of super bike took the focus off the CB450 Super Sport in a dramatic way. From then on the 450 was a sad sister to the more powerful and very successful four cylinder sibling.

However, the initial Honda CB750 had a single overhead cam construction. The venerable four didn't get dual overhead cams until 1979, almost 15 years after the first DOHC CB450. Black Bomber enthusiast will always have that fact to smile about.

Improvements in the engine and bike design accompanied the next version. Disc brakes were added to the K3 model in 1970. Other new features included a larger tail light, hinged gas cap, black-finished handlebar switches, fully rubber cushioned instruments replacing the old "oval" design, and restyled mufflers. The headlight shell and upper fork brackets were painted to match the tank and sidecover color. Gaiters were added to the front shock tubes to keep out dust and moisture.

In 1970 Honda color choices on various models also began to expand, moving beyond the traditional black, silver, candy red, or candy blue to include candy gold. Unfortunately, the original candy red and candy gold finishes are extremely vulnerable to sun fade. The candy blue Honda used is remarkably stable. The CB450 K3 was the last model to include significant engineering as well as styling changes. Most modifications through the CB450 K7 were minor and cosmetic only.

The CB450 was produced until the 1974 K7 model. The next year Honda produced the first Gold Wing, and the CB450 became a thing of the past. The date the “Bomber” went on sale is a dividing line in motorcycle history. Before that date, Japanese motorcycle manufacturers weren’t taken seriously in the world market. After that date, they were. The Bomber showed its competitors that Honda could not only match what other manufacturers were doing, it could go far beyond them in technological development.

Building on the advances of the Super Hawk, the Black Bomber led the way to future designs such as the CB750 and the Gold Wing. Remnants of the CB450 can still be seen in the latest products from Honda … if you know where to look. Once you figure out the best way to do something, there is no longer a need for change. Applies to motorcycles and to life too. Think about that for a while. As for me, I'm going for a ride. See yah!


Honda Dream CA77


Honda Scrambler CL77


Honda Super Hawk CB77


Honda CB450 K0 "Black Bomber"



Honda CB450 K0 Air Filter Cover


Honda CB450 K1


Honda CB450 K3 (Disc Brakes)

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