Let’s face it—the in-line four-cylinder engine in a motorcycle was really nothing new when Honda rolled out the CB750K0 at the Tokyo Motor Show in 1968 to be available in showrooms for the 1969 model year.
In 1917, the French Militaire Champion came with a 1,306cc inlet-over-exhaust in-line four, Cleveland built a bike with a 750cc four-stroke in-line four in 1926, Ace offered a model with a 1,299cc inlet-over-exhaust in-line four in 1923, Italian brand Garabello offered a liquid-cooled inline-four in 1926, Henderson had a model with a 1,301cc in-line four in 1913 and Laurin & Klement offered an in-line four as early as 1905 to name a few.
Of course, all these motorcycle brands and a number of others like them have one thing in common: they are all extinct (although some such as Laurin & Klement which is now Škoda Auto went on in other lines of business.
So, while the idea of an in-line four-cylinder engine in a motorcycle was not revolutionary or all-new, the way Honda came at it was.
First, Honda designed the CB750K0 to be produced in huge numbers. As unique as it seemed, it was designed to be highly standardized, thus capitalizing on the economies of scale. It worked, and in many ways, the CB750 became the standard all other motorcycle manufacturers worked hard to meet or beat.
It was the first modern motorcycle to offer that four-cylinder, transversely mounted, air-cooled engine, it was the first production bike with a front disc brake, five-speed transmission and electric start all in one sleek, refined—and perhaps most important of all–affordable package.
How was the CB750K0 welcomed? Effusively. The bike appeared on the cover of the January 1969 issue of Cycle World magazine and the article about it opened by saying, “Honda Launches the Ultimate Weapon in One-Upmanship — a Magnificent, Musclebound, Racer for the Road.” From then on, the motorcycle industry would never be the same, and Honda wasn’t done.
The media and buying public had barely stopped hyperventilating over the CB750 inline-four when Honda struck again, introducing the CB500K0 in 1971. As you might expect, the CB500K0 four also got the cover shot treatment from Cycle World as well as most other enthusiast magazines then in print. In its feature article on the CB500 Cycle World touted it as “Like the 750, a brilliant highway machine, but smaller, quieter and easier to manage.”
Both the 750 and the 500 benefitted in the marketplace from Honda’s already well-established reputation for rock-ribbed reliability.
I’m fortunate to have a 1973 CB500K2 in my shed, which I bought after a long search for as original an example as I could find. That bike is currently in the prep phase for run (hopefully) at Bonneville in 2022 after being in dry storage for nearly 17 years, after the replacement of an old after-market exhaust system with brand new OEM-spec pipes the old Honda makes a sweet sound down the road.
Honda won a series of world championships in GP racing with incredible high-revving small-displacement four, five, and six-cylinder road racing bikes in the 1960s. In 1972, Honda took the world by surprise and instead of bumping displacement up from the 750, say to 1,000cc, trended the in-line four down to a 350.
Nothing quite like it had ever been seen in the 350cc displacement category. It had the big-bike look, feel, and sound riders craved after having their appetites for four-cylinder power whetted by the 750 and the 500, but with less bulk and a smaller price tag.
Honda was still building the 350cc twin when it introduced the four, so comparisons between the two were unavoidable, but in the end moot. The twin was quicker in the quarter-mile by a bit, but the four could pull a little more on top-end if given enough time. The twin cost less, but vibrated much more. So, if you wanted the smoothness of a four, could wait a little longer to get the thing wound out, and had a little more money to spend, the choice was available.
By 1975, the CB350F was replaced by the CB400F, which in both form and function moved closer to a factory café racer. Honda bumped the basic CB350F engine up to 408cc, increased the valve sizes, added new cases to accommodate a six-speed vs. five-speed transmission, a racer-esque four-into-one exhaust with cool, zig-zag header pipes, and lower, flat handlebars.
The next step in the progression of Honda’s remaking of the high-performance motorcycle market took a lot of experts and enthusiasts alike by surprise.
Instead of something yet more dramatic with engine performance, it was an effort to bring more riders into the sport by eliminating a rider challenge that up till then had been perceived as a roadblock to new riders: the hand-operated clutch.
In 1976, Honda rolled out the CB750A Hondamatic. The name is something of a misnomer because the transmission was not an automatic at all—at least not in the sense that the transmission shifts for the rider as an automatic does in a car. The Hondamatic merely eliminated the need to operate a clutch.
The lever where the clutch is on a manual transmission motorcycle is the parking brake on a Hondamatic, which is necessary since the engine has no mechanical connection to the transmission, thus allowing the bike to roll even if the bike is left in gear when parked. The parking brake requires two hands to operate by design to prevent unintended application while in motion.
The Hondamatic was unique in the industry at the time but it seemed an odd choice to introduce it on a 750 if at least part of the goal was to attract new riders to the fold. That question was answered in 1978 with the introduction of the CB400A Hondamatic—much more in the weight and power class a beginning rider would be comfortable with—but, I digress.
In 1979, the in-line four-cylinder engine got a significant upgrade, changing from a single overhead cam (SOHC) configuration to a double overhead cam (DOHC) arrangement.
That change allowed for valve train improvements, combustion chamber configuration changes, and better breathing, resulting in the ability to squeeze ever more horsepower out of the same displacement.
That led to the much more muscular CB1100R in 1981, which was campaigned successfully by Ron Haslam and Wayne Gardner. By 1992, Honda introduced the first liquid-cooled in-line DOHC four with the CB1000R. In 1998, the top-of-the-line displacement for in-line fours reached 1300cc with the CB1300. In 2006, the technological advancement of the line continued with the addition of EFI and ABS on the CB1300 Super Bol D’Or.
In 2018 Honda added the new Neo Sports Café range, unveiled at EICMA 2017 with the CB1000R as the flagship of the line along with the introduction of the CB300R and CB125R.
In 2019, fifty years after the CB750, the CB650R became the fourth member of the Neo Sports Café lineup and continued Honda’s tradition of inline four-cylinder middleweights. The howl of Honda’s in-line fours goes on in 2021 with models such as the CBR600RR, CBR1000RR-R FIREBLADE, CB1000R Black Edition, and CB650R ABS.