History of Honda CB750

History Honda CB750

With Ian Fallon

Until the late 1960s, motorcycles with four-cylinder engines were unfamiliar and expensive. Emphasizing smoothness, elegance and power, for most people, the number four is just a dream.

The Gilera quartet and MV Agusta dominated the 500 cc Grand Prix throughout the 1950s and were joined by Honda in the 1960s. But these are exotic racing machines, a far cry from the price parallel twins. The UK is dominating the large displacement motorcycle market.

As for production motorcycles, in 1969 the square 4-wheel Ariel was a distant memory, and the Henderson 4-wheeler of the early 20th century even more so. The only other four available are the extremely expensive and hard-to-find 600 cc MV Agusta and the equally exotic Munch Mammut.

After Honda introduced the CB750, KO motorcycle engineering immediately leapt forward a generation. The CB750 offers a refinement and courtesy that was unmatched before and it immediately became the standard by which all others were judged. Mass-produced in large quantities, it also offers technological superiority at an affordable price.

Traditionalists worry that it is too complicated and unreliable, but these views are unfounded. Honda has been successful in high-pressure multi-cylinder bike races for years, and their street machine has a reputation for reliability. Up until the CB750, vertical twin motorcycles dominated, but this changed overnight.

The beginnings of the CB750 go back to early 1968. Honda was about to retire from the Grand Prix, and with their flagship CB450 struggling in the market, Soichiro Honda came up with the idea to build one. “King of Motorbikes”. At the time, speculation was that the new engine would be based on the existing twin-cylinder N360 car, but in February 1968 Bob Hansen from American Honda changed this.

Hansen (Group Manager of CR450s at Daytona in 1967) mentioned to Soichiro Honda that they should develop a four-cylinder machine. Over the next six months, the head of R&D, Yoshiro Harada, and stylist Einosuke Miyachi produced a prototype CB750. The first public display was at the Tokyo Exhibition in October 1968, and by June 1969 the first models were available in the US.

The early production models included some differences from later models, but had some initial problems. Many of these are quite serious, and within the first year Honda released 100 pages of technical updates and newsletters. The newly formed Four Owners Club in America even wrote to Congress and the Governor of California (then Ronald Reagan) complaining about these problems.

Up to the number 1007414, the engine case was cast almost to perfection, looking like it was cast in sand. This is because Honda did not anticipate the demand would be too strong and did not aim for mass production on a large scale. A large number of these early CB750 “sandcasts” were produced (53,399 units), and despite their problems, they have become the most sought-after in the genre.

The CB750’s four-cylinder engine incorporates many differences from Honda’s usual practice. The sub-square dimensions (61 x 63 mm) were chosen to minimize engine width and the crankshaft is forged monolithic with five plain main bearings and relatively small (36 mm) bearings.

Main drive is by an endless double chain drive from the center of the crank to a multi-disc clutch and an indirect five-speed transmission. A single row chain drives the single overhead camshaft while the one-piece cylinder head has two valves per cylinder (32 mm intake and 28 mm exhaust), positioned at a relatively shallow valve cover angle. is 60 degrees.

Four die-cast alloy pistons provide a 9:1 compression ratio and the carburetors are four 28 mm circular slide Keihin carburetors. One difference from the standard Honda is to lubricate the dry sump with a frame-mounted oil tank. Ignition is by points and coils, with two sets of points positioned at the right end of the crankshaft, while an automotive-style 210-watt three-phase alternator is at the other.

The 12-volt electrical system includes an electric starter motor, ensuring a new generation of riders can experience the 750 cc motorcycle. There is no longer a natural choice for riders due to their ability to start their motorcycle and the electrical system is so reliable that the CB750 can be driven across the country without fear of breakdown.

The output power of the 736 cc four is a moderate 67 hp at 8,000 rpm, but this is still significantly higher than the 58 hp of the trio of rivals BSA and Triumph. It is also enough to reach a top speed of around 200 km/h, making it one of the fastest bikes on the market. Compared to its British rival, it also runs quieter, stops much better, and can accelerate over 400 meters stationary in 13 seconds over and over again without breaking down.

The heavy four-cylinder engine (78 kg) was at the heart of the CB750, but as is often the case with Japanese motorcycles of the period, the chassis wasn’t as impressive. A dry weight of 218 kg and reasonable strength have minimized the twin cradle light steel frame and Showa suspension.

The front fork stands out with its alloy kickstand and rubber muffler, but the 35mm fork tube is a bit weak and the drive shaft is still ball-bearing. The swingarm is a two-piece welded stamping rather than regular tubular steel, and the rear shock may be de Carbon, but the only adjustment is a three-way preload spring.

Fully chrome plated with spring top caps, they look a lot better than they function. 19-inch front and 18-inch rear spokes were common for large displacement motorcycles of the era, but 3.25 x 19 and 4.00 x 18-inch Dunlop or Bridgestone tires were made in Japan. particularly hard and slippery.

The most interesting chassis component is undoubtedly the front brake, which is said to be the world’s first hydraulic disc brake on a production motorcycle. To maintain the clean look, Honda has fitted a 300 mm stainless steel front disc instead of the high-grade but rusty cast iron.

They also installed a finned Tokico single-piston floating-piston caliper, which is also inferior to the opposing twin-piston caliper favored by racers. The basic impression of the chassis specification is that that function is of a secondary form, and in this respect the CB750 still has a lot to look forward to.

Where the CB750 really scores is in the looks and finish. From the four distinctive chrome mufflers to the rather rough 16-liter fuel tank, the CB750 is impressive and one of the more compelling Japanese offerings of its time. It may be heavy, long, tall and wide, but the CB750 is the perfect bike for the American, where responsive handling is considered less important than reliability and load-carrying capacity.

In September 1970, the significantly modified CB750 K1 replaced the CB750. Updates include a new seat and black air cleaner box. Production increased to 77,000 units before the CB750 K2 replaced it in March 1972. It took a seasoned expert to tell the difference between the CB750K1 and K2, but on the surface there were stands. new chrome headlights and dashboard with four warning lights, borrowed from the CB500. The quieter exhaust system is certainly the cause of the reduced performance, but Honda continues to grow and total production still reaches 63,500 units.

The CB750 K3 1973 received a new fuel tank stripe and some engine modifications to reduce oil consumption and noise. Performance drops further, but the suspension now includes the usual five-way adjustable rear shock. Apart from the colors, the 1974 CB750 K4 is similar to the K3 but so far the Kawasaki 903 cc Z1 has usurped the CB750 to become the top production roadster.

This still didn’t stop Honda from selling 60,000 units of the CB750 K4 to become the best-selling motorcycle in the US in 1974. At the same time, it received a few minor updates and, although not the fastest Superbike, was countless. Innovation and attention to detail have ensured its popularity. For 1975, the CB750 K5 was little changed but was usurped by the GL1000 Gold Wing as Honda’s range-topping model.

Although the CB750 didn’t offer any technical breakthroughs, it benefited from innovative manufacturing techniques developed by Honda in the 1960s. The first CB750 was a powerful, visceral and powerful motorcycle. interesting, gradually cleaned over its lifespan. As capacity drops, in just a few years, the CB750 is no longer the king of performance.

By 1977, with the name CB750K, it was only a shadow of its former self. But back in 1969, the CB750 was the most important motorcycle to come out in 30 years and possibly the most important production motorcycle of all time. The CB750 was so influential that horizontal inline 4-cylinder engines became popular and dominant.

This year, 2023, Honda will launch a CB750 powered by a brand new twin.

Specifications Honda CB750 K1