The Enduring Heart of the Honda CX500

In the late 1970s, the motorcycle world was largely dominated by perceptions shaped by big, tough American cruisers. However, Honda, ever the innovator, sought to redefine what a motorcycle could be. Their answer arrived in 1978: the Honda CX500. Billed with the audacious headline “First into the future,” this machine truly aimed to be a game-changer, not just in its aesthetics but, crucially, in its engineering. This article delves deep into the heart of the Honda CX500 – its remarkable engine – exploring its unique design, the significant upgrades it received, and its lasting legacy, even finding new life in bespoke British kit cars and cafe racer projects.

The Revolutionary V-Twin Heart

At the core of the Honda CX500's groundbreaking vision was its engine, a testament to Honda's commitment to pushing boundaries. Designed by the visionary Shoichiro Irimajiri, this wasn't just another motorcycle power plant; it was a carefully engineered statement.

Pushrod Power and Four-Valve Innovation

The single biggest development that came from the Honda CX500 was the inclusion of a pushrod engine instead of the more common overhead cam design. While the concept of water-cooling a motorcycle engine wasn't entirely new, applying it to a V-twin was a significant first for Honda. But the innovation didn't stop there. Uniquely for a pushrod engine of its time, the CX500 featured four valves per cylinder. This configuration, while making the engine a bit taller than many contemporaries, delivered abundant low-end torque and produced a distinctive, appealing sound that set it apart.

This pioneering design contributed to the CX500's reputation for robustness. While a few common issues did arise – namely, timing tensioners could develop problems (though easily replaceable) and valves occasionally went out of adjustment (also fixable) – these were generally minor in the grand scheme of its overall durability. Even small issues with the cooling and exhaust systems were infrequent. The 497cc engine was also remarkably fuel-efficient, often achieving 45 miles per gallon or more, making it a practical choice for everyday riders.

The CX500 in Kit Car Culture: The JZR

The Honda CX500 engine's reliability and distinctive character didn't just appeal to motorcyclists; they also caught the attention of niche automotive manufacturers. From their workshop in Darwen, Lancashire, John Ziemba Restorations began marketing the JZR three-wheeler kit car in 1990. Inspired by classic Morgan Aero three-wheelers and more recent designs like the Triking, the JZR initially relied on the robust Honda CX500 V-twin as its primary power source. This adoption into the bespoke world of kit cars, where engines are chosen for their proven performance and ease of integration, speaks volumes about the CX500's inherent quality and versatility. While later JZR models incorporated other Honda engines (CX650, CX500/650 Turbo, Pan-European ST1100 V4) and even Moto Guzzi and Harley-Davidson motors, the CX500 was the original heart of many of the 320 JZRs produced between 1990 and 1998, and continues to be used in its ongoing production today. The power was reliably transferred to the rear via shaft drive, mirroring the motorcycle's original setup.

Evolution and Refinements: CX500 Upgrades

Despite its initially polarising looks – with some media outlets even comparing it to an "air compressor" – the CX500 quickly garnered a loyal following, particularly among commuters and long-haul riders. Honda responded to customer feedback and market demands by introducing a series of thoughtful upgrades and trim levels throughout its production run from 1978 to 1983.

Trim Levels and Comfort Enhancements

Early in its life, the CX500 saw the addition of 'Custom' and 'Deluxe' trims. The 'Custom' model directly addressed customer complaints about the standard tank's width by featuring a smaller, narrower fuel tank. It also incorporated buckhorn handlebars and turn signals mounted to the fork tubes, offering a different ergonomic and aesthetic package. The 'Deluxe' trim maintained a closer resemblance to the standard model but included subtle changes to the gauges and a bit of extra trim, aiming for a more premium feel. Later, the 'Silver Wing' editions were introduced, offering an optional factory-fitted rear-mounted accessory box, enhancing the bike's touring capabilities.

Pioneering Fuel Injection and Turbocharging

The 1982 model year marked a significant milestone for Honda, as the CX500 became the company's first motorcycle to feature a programmable fuel injection system. This technological leap improved fuel delivery and efficiency, further cementing the CX500's reputation as a forward-thinking machine. The bike's relatively open design and the ease with which its mechanics could be understood also made it popular in college mechanic's courses, proving its educational value.

Perhaps the most dramatic upgrade came with the introduction of the Honda CX500 Turbo. This revolutionary addition nearly doubled the engine's output, a staggering achievement for the era. Honda engineered the CX500 Turbo with increased compression, resulting in a smooth ride with minimal turbo lag or lash, a common issue with early turbocharged vehicles. Despite the added complexity of a turbocharger, these engines largely retained the CX500's renowned reliability, a testament to their robust design. Many used CX500 Turbo models remain available today, often in excellent condition, cherished by loyal owners. The availability of parts for all CX500 variants also remains strong, further contributing to their enduring popularity.

Built to Last: Reliability and Common Quirks

The Honda CX500's reputation for reliability is legendary. It’s a testament to its robust construction that many examples built in the late 1970s and early 1980s are still on the road today, often with their primary concern being the title, not the bike's mechanical integrity. This inherent durability earned it an endearing, if slightly unflattering, nickname: the "plastic maggot." This term wasn't just a jab at its appearance; it was a nod to just how much abuse the CX500 and its engine could withstand, yet still keep running. While not the fastest big CC cruiser, its consistent performance and affordability made it a welcome addition to the world of road bikes.

As with any machine, the CX500 did have a few common quirks, but these were generally minor and manageable. Timing tensioners were known to develop issues, but replacements were readily available. Valves could go out of adjustment over time, but this was a fixable maintenance item. Some riders also reported minor issues with the cooling and exhaust systems, but these were not widespread or debilitating. The overall consensus remained that the CX500 was a workhorse, a bike that could add a new chapter to the motorcycle genre without demanding constant attention or costly repairs.

The CX500 Chassis: More Than Just an Engine

While the engine was undoubtedly the star, the CX500’s chassis was also thoughtfully designed, contributing to its unique ride characteristics. It featured thicker splines than most bikes of its time, providing enhanced support, partly due to its relatively heavy weight for a small motorcycle at 441 pounds. Early models sported hydraulic front shocks, complemented by a dual spring-over-telescopic shock absorber system at the rear. While riders might not have boasted about plush comfort, this setup effectively absorbed road impacts, particularly beneficial for city commuters, and contributed to a tight, well-balanced ride.

A clever design choice was the 5-speed transmission, which rotated in the opposite direction to the engine. This ingenious counter-rotation helped to significantly reduce the amount of "twisting" felt by riders, a common characteristic in shaft-driven bikes. Furthermore, mounting the engine over the transmission resulted in a shorter transmission unit, though it did make the bike itself taller than average. Initial models featured a single disc brake at the front and a drum brake at the rear. Notably, the CX500 was also the first production motorcycle to be fitted with tubeless tyres, another nod to Honda's forward-thinking approach. The combination of balanced transmission gears and engine rotation contributed to a ride that many enthusiasts found surprisingly light for a tall bike, and its torque and comfortable feel made it particularly appealing to younger audiences.

A Legacy Forged in Steel: Cultural Impact

Despite its initial mixed reception – epitomised by the "plastic maggot" moniker – the Honda CX500 quickly made its mark. Wheels Australia, a prominent publication, even named it their "Bike of the Year" in 1978. While some traditional cruiser riders initially disliked its unconventional styling, the CX500's strengths lay in its practicality, durability, and the sheer fun it offered. It represented a new chapter in motorcycle design, proving that a bike didn't have to be a massive, chrome-laden machine to be significant. Its robust nature and relatively low running costs ensured its longevity, cementing its place as a reliable and accessible road bike.

Reviving a Legend: The CX500 Cafe Racer Build

The inherent robustness and straightforward mechanics of the Honda CX500 engine have made it a perennial favourite for customisation projects, particularly cafe racers. The detailed account of a 1982 Honda CX500 cafe racer build thread offers a fascinating insight into the engine's internal workings and the dedication required to transform these classic machines. This particular builder, despite having very little prior experience, embarked on an ambitious project, demonstrating the accessibility of the CX500 as a platform for learning and modification.

The Builder's Journey: Learning Through Disassembly

Driven by a desire to understand the "heart of this motorcycle," the builder decided to undertake a full engine strip-down and rebuild, replacing seals, gaskets, and bearings where necessary. This hands-on approach, inspired by online communities and manuals, proved invaluable for learning. The process began with meticulous disassembly, followed by the lengthy and challenging task of cleaning each component. The builder employed various methods, from Scotch-brite scourers and hours of scrubbing to using a sandblasting cabinet with walnut shell for a pristine finish, followed by a pressure wash and thorough drying.

Painstaking Restoration: Cleaning and Polishing

Once clean, the components underwent a transformation. Parts intended for painting were carefully taped off, then treated with three coats of VHT Engine enamel primer and three coats of VHT Black Pearl, followed by an hour in an oven at approximately 90 degrees Celsius for curing. Some parts, like the fins of the oil filter housing and sections of the engine block, were polished on a bench lathe using various cutting compounds to achieve a pleasing, though not mirror, shine. The rocker cover also received a similar polishing treatment, though polishing between its fins proved a challenge.

Precision Reassembly: Inside the Engine

A crucial step involved checking all parts against the specifications in the manual. Remarkably, after 85,000 kilometres over 35 years, there was no significant wear on most measured components, a true testament to the engine's longevity. Despite this, the builder opted to replace bearings where possible, navigating the difficulty of sourcing specific big end shells. Plastigauge was used to meticulously check oil clearances at the crank pin and bearing interface, ensuring proper fitment.

New piston rings were fitted after honing the cylinders with an inexpensive tool and a cordless drill to create the essential criss-cross pattern. The pistons and con-rods were carefully installed. The rear crankcase cover, a pressure-fit component, required extreme care during removal to avoid damaging the oil bearing, which in this case showed signs of previous damage or pitting. Sourcing a replacement bearing that wasn't an exact match presented a challenge, requiring a calculated risk on a slightly tighter fit.

The transmission assembly saw new mainshaft and countershaft bearings installed in both the holder and the case. New clutch friction plates and springs were fitted, and a custom tool was fashioned to lock the crankshaft for tightening the clutch lock nut to its high specified torque. The oil pump was put in place, and the front cover prepared for sealing with a new gasket, highlighting the importance of keeping track of numerous small parts during a long-term build. New stainless steel hex head bolts were used for a refined look against the black engine.

Inside the engine, cam followers were well lubricated before the greased camshaft was carefully inserted. The automatic cam chain tensioner and cam mechanism were put in place, with all parameters checked against the manual for correct timing. A practical upgrade involved replacing the factory Phillips head tacho gear adjustment screw with a hex head for easier access once the bike is assembled. New oil seals were fitted, including for the mechanical cam-driven fan, with plans to replace it with an electric fan requiring modification to the camshaft. The clutch cover and flywheel were reinstalled, along with new final shaft and gear shift spindle seals, with minor paint touch-ups planned. The water pump's mechanical and oil seals were also replaced. The valves underwent thorough cleaning, a process demonstrated in online videos, followed by lapping to ensure perfect seating, despite the valve seat cuts being in good condition but carbonised. New valve stem seals were fitted, and the block prepared for the heads, with new O-rings for oil orifices and new head gaskets and sealant. Finally, the push rods and rockers were installed, tappets set, and the rocker cover secured, awaiting a replacement locating dowel.

Frequently Asked Questions About the CX500

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