The Enduring Legacy of the Honda CX500 Engine

When it first roared onto the scene, the Honda CX500 was nothing short of a revelation. It wasn't just another motorcycle; it was a bold statement, packed with innovations that set it apart from its contemporaries. As the first mass-produced motorcycle to feature tubeless wheels, alongside the legendary CBX, it immediately carved out its own niche. Despite its peculiar, often criticised design – unusually large and heavy for a 500cc machine – it possessed an undeniable charm and, more importantly, a remarkable capability. While not without its quirks, the CX500 offered a compromise that resonated deeply with many riders, proving itself a surprisingly effective package for the 1978 model year in its class.

At the heart of this unconventional machine lay an engine with an equally intriguing backstory. The powerplant that drove the CX500 was originally conceived not for a motorcycle, but for a small car. This automotive lineage perhaps explains some of its robust, over-engineered characteristics. Curiously, the initial production run of these engines yielded noticeably more power than subsequent iterations. Early models were capable of reaching impressive top speeds of up to 187 kph (116 mph) and could sprint from 0 to 100 kph (0-62 mph) in a brisk 5.4 seconds, completing a standing start quarter-mile in a mere 13.4 seconds. These figures were achieved thanks to a genuine 50 horsepower delivered at the crank, precisely as Honda had promised in their marketing pamphlets. However, for reasons that remain somewhat shrouded in mystery, the power output soon dropped, settling into the 42-43 hp range, even though Honda continued to quote the original specifications. This reduction in power naturally led to more typical top speeds of just over 170 kph (105 mph) and correspondingly slower acceleration.

The Unconventional Heart: Design and Engineering

The CX engine was, by any measure, highly unconventional, and to this day, its unique design has never been replicated in mass production. To achieve a narrow engine profile, crucial for motorcycle ergonomics, Honda engineered it as an 80-degree V-twin. While a 90-degree V-twin offers theoretically perfect primary balance, the 80-degree configuration resulted in a slightly less than ideal balance. However, through meticulous engineering and clever balancing techniques, Honda managed to minimise any penalty in the form of vibrations. In fact, many riders found the CX to run smoother than even a Moto Guzzi, despite the latter's theoretically perfect 90-degree cylinder splay.

Liquid cooling, a commonplace feature today, was still considered somewhat exotic for motorcycles when the CX was unveiled to the press at the end of 1977. Yet, it played a crucial role in the CX's design, effectively controlling both noise emissions and engine temperature. An interesting design choice was the cooling fan, which was directly driven from the camshaft. While functional, this setup often led to overcooling, particularly in cooler climates or at lower speeds. Recognising this, Honda made several revisions with the introduction of the GL500 in 1981. This updated engine received an automatic cam chain adjuster, a switch from CDI to TCI ignition, and a more efficient electric cooling fan, addressing some of the earlier model's quirks.

Another distinctive feature was the 22-degree splay of the cylinder heads. This ingenious design choice was made to angle the carburettors outwards, moving them away from the rider’s feet, thus improving ergonomics and comfort. This design necessitated a departure from Honda’s usual Overhead Cam (OHC) configuration, leading them to adopt an Overhead Valve (OHV) design with pushrods. While OHV systems were often considered obsolete and somewhat 'agricultural' by many enthusiasts, the little Honda engine defied expectations. It could still reliably rev to an astonishing 11,000 rpm before valve float became an issue. Honda even claimed their engineers could make the engine reliably rev to 12,500 rpm. For the production model, the redline was conservatively set at 9700 rpm, but the owner's manual explicitly stated that the engine could be revved to 10,500 rpm for short bursts during hard acceleration, showcasing its inherent robustness.

Maintenance and Reliability: A Mixed Bag

Despite its novel and effective cooling system, the CX was not entirely trouble-free. A notable Achilles' heel was the cam chain tensioner, which proved to be too weak and prone to breakage. Unlike many engines where such a failure would lead to immediate and catastrophic destruction, the CX's design often prevented this, though the alarming noise from a flapping cam chain was certainly enough to get any rider's attention. It took Honda several attempts and a couple of years to fully resolve this persistent cam chain tensioner malady, eventually providing a more robust solution.

However, beyond this specific issue, the Honda CX was remarkably easy to maintain for its era. Valve access, for instance, couldn't have been simpler, allowing for quick adjustments that took only a few minutes. The clutch was conveniently located at the front of the engine, adjacent to the oil filter cartridge. Perhaps one of the most innovative features was the gearbox, which could be removed as a self-contained cassette unit. While this modular design was fantastic, gaining access to the gearbox, cam chain, and ignition still required the engine to be removed from the frame. This might sound like a daunting task, but it was, in reality, a rather straightforward process. Given that the engine was an integral, stressed member of the frame, there were no traditional down-tubes to contend with. The frame could essentially be lifted off the engine in a matter of hours, leaving the engine freestanding and accessible. While not quite as simple as the process for a Moto Guzzi small block, it was considerably easier than disassembling a BMW airhead, highlighting Honda's thoughtful engineering.

Chassis Dynamics and Drivetrain: Complementing the Engine

Honda marketed the CX500 as a dual-purpose machine, equally adept as a sports bike and a touring companion. In practice, it leaned far more towards the latter. The suspension, for example, was intentionally overly soft, designed to deliver a compliant and comfortable ride. While excellent for cruising, this softness proved inadequate for aggressive cornering or for touring with a heavy load. The aftermarket quickly stepped in to address these limitations, offering air kits for the front forks and heavy-duty shock absorbers for the rear. Even with stiffened front springing, the spindly 33 mm stanchions struggled to provide the precise guidance required for truly spirited riding. Later models in the GL series saw an increase in stanchion diameter to 35 mm, while the turbocharged variant boasted even beefier 37 mm stanchions. Despite these minor handling nuances, the bike performed splendidly for the kind of riding most owners actually engaged in.

The shaft final drive was another significant convenience, particularly for touring riders and commuters who frequently encountered inclement weather, as it eliminated the need for chain maintenance. However, like the suspension, it was not ideal for the sporting rider demanding precise handling. While not as pronounced as the distinctive shaft drive reactions found on period BMWs, the little Honda still exhibited noticeable effects. Under acceleration, the swing arm would be pushed downwards, causing the rear end to rise and stiffening the suspension. Conversely, trailing the throttle would have the opposite effect, robbing the bike of precious cornering clearance and unsettling the suspension. Again, for the vast majority of riders, these subtleties mattered little in their everyday use.

Braking systems also varied across regions. In Europe, the CX family consistently featured twin front discs, providing ample stopping power and receiving few complaints. In contrast, most models sold in the USA were equipped with only a single front disc brake, which was generally found to be lacking in performance. The later EuroSport version further enhanced braking capabilities by replacing the previous drum rear brake with a more modern disc item.

The Progeny: CX500 Variants and Legacy

Over its production lifespan, the versatile CX500 engine powered a remarkable seven different variants, each tailored to a specific segment of the market. These included the CX500A/B, CX500C, CX500D, CX500E, CX500TC, GL500, and GL500I. The A/B, D, and E models were what we would now classify as 'standards' or 'nakeds', offering a more traditional riding experience. The C and GL variants leaned more towards a cruiser aesthetic, with different ergonomics and styling. The CX500TC, a truly groundbreaking machine, featured a turbocharger and a full sports-touring fairing, pushing the boundaries of motorcycle performance. The GL500I, standing for 'Interstate', was designed for long-distance touring, equipped with full luggage and the same distinctive fairing found on the larger Gold Wing 1100, offering unparalleled comfort and convenience.

In 1983, the CX engine underwent a significant enlargement, growing to 673 cc and subsequently being rebranded as the CX650. However, despite its continued evolution and success, Honda made the decision to discontinue the entire CX line at the end of 1983 for most markets. Although production lingered on for another two years in some regions, sales had markedly declined. Nevertheless, with nearly 400,000 CX units sold globally over the years, the Honda CX series stands as one of the company's biggest successes, a testament to its innovative design and enduring appeal, surpassed only perhaps by the monumental market dominance of the CB350 twin a decade earlier. The CX500 engine, with its unique V-twin configuration, liquid cooling, and shaft drive, truly left an indelible mark on motorcycling history.

CX500 Engine Performance Evolution

CX500 Braking Systems

Frequently Asked Questions About the Honda CX500 Engine

Why was the Honda CX500 engine considered so unconventional?

The CX500 engine was unconventional primarily due to its 80-degree V-twin configuration, designed to keep the engine narrow, and its unique cylinder head splay (22 degrees) which allowed for better carburettor clearance. It also used an OHV (pushrod) design, which was considered old-fashioned for its time, yet it could rev to remarkably high RPMs. Furthermore, it was one of the earliest mass-produced motorcycles to feature liquid cooling and a shaft final drive.

What were the main reliability issues with the CX500 engine?

The most notable reliability issue with the CX500 engine was the cam chain tensioner. It was prone to failure due to being too weak, leading to alarming noises from the flapping cam chain. Honda took several years and multiple revisions to fully resolve this problem, eventually introducing a more robust automatic tensioner in later models like the GL500.

How easy was the CX500 engine to maintain?

Despite its complex appearance, many aspects of the CX500 engine were surprisingly easy to maintain. Valve access was straightforward and adjustments took only minutes. The clutch was conveniently located at the front, and the gearbox could be removed as a self-contained cassette. While accessing the gearbox or cam chain required engine removal from the frame, this process was simplified by the engine being a stressed member of the frame, allowing the frame to be lifted off relatively easily.

How many different Honda models utilised the CX500 engine?

The CX500 engine powered seven distinct variants of Honda motorcycles: the CX500A/B, CX500C, CX500D, CX500E, CX500TC (Turbo), GL500, and GL500I (Interstate). Each variant offered a different style and purpose, from standard naked bikes to cruisers, a turbocharged sports-tourer, and a fully-equipped touring machine.

What was the 'shaft drive reaction' on the CX500?

The 'shaft drive reaction' refers to the subtle but noticeable effects of the shaft final drive on the motorcycle's chassis dynamics. On the CX500, under acceleration, the torque from the shaft would tend to push the swing arm downwards, causing the rear end of the bike to subtly rise and stiffen the suspension. Conversely, when rolling off the throttle, the opposite effect occurred, potentially upsetting the suspension and reducing cornering clearance. While present, these effects were less pronounced than on some other shaft-driven motorcycles of the era.

Why did Honda discontinue the CX line?

Honda decided to discontinue the CX line, including the enlarged CX650, at the end of 1983 for most markets, despite its previous success. While the exact reasons are complex, it was likely due to evolving market trends, the introduction of newer, more conventional engine designs, and perhaps a decline in sales volume as the initial novelty wore off. Despite its short production run, the CX series sold nearly 400,000 units, marking it as a significant success for Honda.

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