Honda CX series
|GL500 Silverwing, ST series (influenced)
|500–673 cc water-cooled longitudinal OHV 80° V-twin, 4 valves per cylinder
|50-77 hp (97 hp turbo)
The Honda CX series motorcycles (including the GL500 and GL650 variants) were developed and released in the late 1970s, with production ending in most markets by the mid 1980s. The design included innovative features and technologies that were uncommon or unused at the time such as: liquid cooling, electric-only starting, low-maintenance shaft drive, Com-Star modular wheels, and dual CV-type carburettors that were tuned for reduced emissions. The electronic ignition system was separated from the rest of the electrical system, enabling the motorcycle to be push-started and ridden in case of a total electrical system failure.
In their day these bikes were much favoured by commercial despatch riders in the UK.
It was Honda's plan that the CX series would compete favorably with smaller Moto Guzzi and BMW cycles. Therefore a lot of resources were invested in achieving an optimum design the first time. The CX series motorcycles are considered to be a great all-purpose medium-sized standard with city-bike reliability and heavier short to medium range sport-touring capability. The CX continues to be an increasing fan-base to the present day and are having a renaissance as people find older examples worthy of restoration.
The CX series motorcycles feature a crankshaft configuration aligned longitudinally with the axis of bike, sometimes called a "flying" V-twin, because the cylinders point up on either side of the motorcycle but are not symmetrical. The CX was the first V-twin motorcycle that Honda ever built. Honda built a prototype CX350 but it was never released to the public. In this version the cylinders did not have the characteristic 22 degree twist. Initially conceived as having a full 90 degree angle between the cylinders like the similar Italian Moto Guzzi machines, early testers reported that the prototypes were too smooth. Also, the carburettors, which projected directly rearward from the cylinders, tended to interfere with the knees of riders. Subsequent engine designs had their V-angle tightened somewhat to 80 degrees, and the heads twisted inward at the rear by 22 degrees.
An innovative design places the crankshaft *above* the transmission, with both in the same housing. This keeps the engine short but quite tall.
The engine design combines a 10.0:1 compression ratio and 9,650 rpm redline with overhead valves and a camshaft nestled at the base of the V between the cylinders. There are four overhead valves per cylinder, with unique forked rocker arms acting off each pushrod. The engine runs well on 87 octane petrol. It delivers nearly 50 hp (37 kW) at 9500 rpm with high low-speed torque characteristics. The Honda CX series machines claimed to outperform other motorcycles of comparable displacement. The motorcycle readily achieves a fuel efficiency of 45 miles per gallon, with figures of over 50 mpg not at all uncommon . Moto Guzzi, however, with their contemporary V50 Monza, delivered 48 hp at 7600 rpm. This was from an aircooled, 2 valve 90° V-twin which delivered well over 55 mpg but also had the standard Italian foibles of the time with its questionable electric reliability. This Guzzi model is little known outside Europe, so a direct comparison with Honda's CX 500 is possible only on paper or amongst motorcycle enthusiasts.
The cylinder bores are cast in the crankcase which complicates the overhaul process although many examples have gone 200,000 miles or more without any major engine work.
The transmission spins opposite the engine crank to counteract the engine torque's tendency to tip the bike slightly to one side when the throttle is opened or closed. The gear shift lever is moved with the usual up-down motion of the left foot, but instead of rocking in a forward-backward motion as on regular bikes, it moves left-right. This difference is transparent to the rider, however, and requires no change in shifting technique. It also means that it is not possible to adjust foot peg and gear lever setup when personalizing riding position.
Power is transferred via an enclosed splined driveshaft with one universal joint. The shaft drives a bevel gear to which the wheel is joined via a cush-drive, which absorbs and dampens driveline shocks and vibrations. The bevel drive spins in an oil bath, and a zerk fitting is provided for greasing the shaft bearing. This reduces the motorcycle's maintenance costs.
The original Com-Star wheels combine the flexibility of spoked wheels (without the maintenance burden) with the strength and tubeless characteristics of one-piece wheels. This was one of the first production motorcycles to be equipped with tubeless tires, Honda having introduced this technology a year or so earlier on the CB250T/400T Dream.
Early versions had conventional suspension, consisting of hydraulically damped telescoping front forks and dual coil-over shocks at the rear. Later versions had air-assisted forks and featured Honda's Pro-Link monoshock rear suspension. US bikes (except GL500I, GL650I and Turbo) were equipped with a single front disk brake whereas all other bike possess dual front disk brakes. Models after 1980 sport dual piston callipers replacing the single piston calliper of the earlier models. For the Turbo and Eurosport models the rear drum was replaced with a dual piston calliper and disk. All models feature steel tube frames with a large backbone, with the engine used as a stressed member. The dual shock models use a single tube backbone whereas the later Pro-Link models employed a triple tube backbone. Later models are blessed with larger front forks which provides a noticeable improvement in handling.The European models have two brake disks on the frontwheel whereas the American versions only have one.
The original 1978 CX500 originally had a poorly designed cam chain guide location position and in the very early release demonstration models, weak big end bearing/oil supply design. The big end problem was only experienced on the initial press test bikes. Failure of the lower cam chain guide location bolt could also cause catastrophic cam chain failure and resulting damage to the related reciprocating parts. There were factory recalls to rectify the cam chain issue with varied success. If the repair was done at the dealership, there will be three punch marks in the shape of a triangle next to the serial number on the engine. The original CX500 evolved through the 1979 500A and B models before being replaced by the Eurosport 500 in 1983. Even into the late 90's the CX was still being used by couriers in London, England as they became almost indestructible when used in this manner and maintained accordingly.
There are only four real problems to worry about on a CX500. The stator, the CDI box, the cam chain, and the water pump seal. The CDI units can be got off Ebay 2nd hand or there are CX enthusiasts who have made their own  Stators in the 1978-1981 CX500 serve two purposes; it charges the battery, and it provides high voltage (90+ volts) to the CDI box to run the ignition system. Stators are located in the rear of the engine, and they get very, very hot. This heat eventually causes the stator to fail. Usually only one of the three windings fail: Charging, low speed (no advance), or high speed (full advance) winding. When the charging winding fails, the battery does not charge. When the high speed winding fails, the bike will not accelerate well past 3500 rpm, when it switches over to the high speed winding. If the low speed winding fails, the bike will not start, and will have no spark or intermittent spark. In practice, usually the high speed or charging windings fail.
Note that the 1982 CX500, all GL500's, and the 83 CX650 and GL650 have different stators which only contain charging windings. These bikes have a transistorized ignition system that is extremely reliable. The stators run cooler without the two high voltage windings, so they are somewhat less prone to failing like the CDI stators. But they still do fail. Note also that the regulator/rectifier for these models is different from the previous years; the plugs are incompatible.
Water pump seals on these bikes deteriorate with age. The seal is a simple rubber and ceramic design, and if a bike sits for any length of time the seal can stick together, and when the bike is started it will self-destruct. Water pump seals can also fail on a bike that is ridden regularly if the wrong type of coolant is used but this has been challenged by quite a few CX/GL owners.It has been suggested that Silicates (tiny pieces of plastic) in normal coolant are used to keep radiators clean by basically sand-blasting away corrosion and calcium deposits. These silicates get between the ceramic and rubber parts of the seal, and will grind and pit the ceramic over time. This may cause the seal to leak.
Back-yard mechanics will commonly try to stop the leak by plugging the drain hole. (or mud wasps will nest in there) This causes the coolant to push past the oil seal on the end of the camshaft, and the coolant gets into the oil. This is often mis-diagnosed as a bad headgasket. Normally the changing of the Water pump seal means taking the engine out but an in situ repair can be done as per Mech Seal
Cam chains on the CX bikes stretch, and are only good for 50,000 miles at the maximum unless you believe this source, . If the cam chain is not regularly tensioned at the proper intervals, it can stretch much faster. When a cam chain stretches (or more uncommonly a tensioner breaks), the chain will make a rattling sound. This sound is the chain contacting the aluminum case and wearing away material. If the bike is run too long in this condition the cam chain will wear completely through one of the tensioner mounting bosses, and the engine will be junk. (Also, aluminum particulates in your oil is not good for bearings). The CX650ED, and in the US, the 1983 CX650 and GL650 have an automatic cam chain tensioner that never needs adjustment. First indication of a stretched cam chain was a 'ting' noise when backing off the throttle and could occur before 65,000 klm (40,000 miles). Unfortunately, this tensioner design is much less reliable than the manual adjuster, and can stick part-way through its adjustment range. This can happen even at a very low mileage, or it might never happen, but it is a somewhat common ailment for the 650 engine.
Finally, the CDI boxes on 1978-1981 CX500s are not ageing gracefully. These boxes are full of big capacitors, and the dielectric fluid in capacitors dries up over time, and can outright fail. Thus, operating CDI boxes are becoming a rarity these days. Usually they fail on one cylinder - intermittently to start, and then completely. CDI boxes are also very easy to kill by high resistances in 30-year-old spark plug wire resistor caps.
A slightly less catastrophic weak point was the plastic mechanical fan used on the 500 engines (but not the 650). Under normal usage they were okay, but prolonged high speed operation could eventually make them shatter, usually destroying the radiator and spraying coolant on the rider's leg.
And finally, not to forget the unlikely (but worth checking as a safety critical part) problem that can occur with the Comstar wheel design, namely the corrosion and loosening of the rivets that secure the centre to the rim which if serious could possibly lead to separation of the two. Ideally the rivets should be regularly checked for corrosion or loose fit, maybe at the same time as washing the bike or checking tyres. There are companies who can repair this type of problem as well as straightening minor rim damage.
The 1978 CX500 Standard had a large fuel tank, stepped seat, a round brake fluid reservoir and a plastic mini-fairing that was thought to look unusual at the time, and gave the bike the nickname "plastic maggot". Turn signals extend out through the mini fairing from the headlight's centerline. The CX500 Standard had silver Comstar wheels, 19 inch in front and 18 inch in the rear.
While V-twins were nothing new, Moto Guzzi had been mounting them "in line" with the frame with shaft drive for many years, this Honda was decidedly different. Not only was the 500 cc engine water cooled, but it had four valves per cylinder that were operated by pushrods rather than more conventional overhead cams. 
The styling was radical, upright forks and a short engine contributed to a stubby wheelbase on a bike that was rather tall. The CX500 was one of the first recipients of Honda's new Comstar wheels (and later, on B models, reverse comstar and a square brake fluid reservoir), which measured 19 inches (480 mm) in front and 18 inches (460 mm) at the back.
The fuel tank tapered toward the front and a huge half-moon tail light jutted out from a short fairing behind the radically stepped seat. The end result was a mix of standard, sport, and cruiser features.
The CX500 met with a good degree of success. It proved to be reliable and economical, being the least-expensive shaft-drive bike. Many examples still exist today, and along with the GL Silverwings, are fast becoming cult bikes. There are owners clubs throughout Europe and the rest of the world.
In 1982, this version of the bike received a turbocharger and a very complex fuel injection system with multiple redundant fail-safe systems. The following year, all CX500s and GL500s were enlarged to 650 (actually 673 cc), and the turbo version got a much simplified fuel injection system. Factory turbos fell out of favor with the motorcycling public for various reasons, causing Honda to cease production of the CX650 Turbo after the 1983 model year.
The CX500T was the world's first turbo-charged production bike, as opposed to the Z1R TC which was fit with an aftermarket RayJay turbo by Turbo Cycle Corporation, before shipment to select Kawasaki dealers. The CX500T also featured fuel injection and a radical fairing. The CX500 Turbo (also known as the CX500TC) was only produced for the 1982 model year and was superseded for the 1983 model year by the CX650 Turbo which was itself based upon the naturally aspirated CX650. The CX500 Turbo was sold only in limited numbers, with a total of around 5,400 manufactured.
The Turbo's powerplant was based on the water-cooled V-twin with four pushrod-operated overhead valves per cylinder used in the shaft-drive CX500 introduced a few years earlier—itself a groundbreaking design. In fact, the engine case was retained nearly intact from the original CX500, having been designed from the outset to accommodate turbo-charging. The turbocharger, at peak boost providing approximately 19 psi of over-pressure, nearly doubles the power output of the engine when on-boost. The engine case is one of the few items carried over from the original CX500; the suspension, brakes, frame and fairing all differ significantly from the earlier CX500. The base engine also was used in the Honda GL500 Silver Wing, a touring machine aimed at being the Gold Wing's little brother, and the CX500C, a custom model with chopper styling.
The CX500 Turbo, although capable of superb acceleration when on-boost, suffers somewhat from an abrupt and large step in power when transitioning from off-boost to on-boost. Furthermore, being the first production Honda motorcycle with fuel-injection, the engine control system is complex and, by current standards, quite bulky, requiring two separate enclosures as well as a number of pressure-carrying hoses.
The "Custom" variant, introduced in 1979, had a smaller, narrower tank and buckhorn handlebars that made the bike more Harley-esque. The headlight and gauges were similar to the CX500 Deluxe. Turn signals were now mounted along the fork tubes, below the level of the headlight. This model set its sights on more of a cruiser style and image-conscious rider.1982 was the last model year for the CX500. In 1983 it was bumped up to 673 cc and became the CX650. The CX650's styling was radically different, and the engine was painted black instead of silver. The CX650 could not compete against the comparably-priced, but much more powerful VF750 Magna, and was dropped the following year.
The "Deluxe" model appeared in 1979. This bike looked nearly identical to the original CX500 Standard, with the exception of regular (85mph) gauges and headlight (the mini fairing was removed) and black reversed Com Star wheels - 19 inch front and 16 inch rear.
In 1981 Honda released the GL500 Silverwing, which was a mid-sized touring bike based on the CX500 engine. The GL500 engine was similar to the CX500 engine, but had the more reliable transistorized ignition system, so that the stator could contain only charging windings, and thus put out more power for operating lights and electronic devices commonly added to touring machines. The GL500 also sported Honda's Pro-Link monoshock rear suspension, and was available both as a naked bike, as well as an Interstate model which included a large factory fairing and hard saddlebags and trunk. This made the Silverwing look like a miniature GL1100 Goldwing. The 1981 model had a small tail trunk, 1982 GL500s and 1983 GL650s had a larger trunk. The trunk was interchangeable with the back seat--the bike is rider-only with the trunk installed, although there was an aftermarket extender available to allow the trunk to be mounted behind the passenger seat. In 1983 the GL500 was upgraded to the GL650, and that was the last model year in the USA. Model years can sometimes be confusing, however, as the 1982 GL500 was seriously overproduced, with some selling new as late as 1984. They should still be titled as 1982s, but there are cases where they haven't been.
The GL650 Silverwing is just a bigger version of the GL500. The frame and all running gear is essentially the same, but the front engine hanger mount and fairing mounts are slightly different, and portions of the engine are painted black. Both Standard and Interstate models were available in burgundy or dark gray paint schemes. This was the only year for the GL650 in the US.
This bike gets better gas mileage than the GL500 due to significantly taller gearing. The 650 engine also finally replaces the CX/GL500's mechanical fan with an electric one. Losing the mechanical fan probably contributes to the better gas mileage as well, but it's uncertain how much.
The CX650 Custom was a one year model produced in 1983 for the US market. Its unique cruiser type styling sets it apart from all other CX variants. The frame is completely different, and the styling was marketed to accommodate the American desire for the low stretched look of American cruiser bikes. Its semi chopped fork, tear drop tank, low seat and truncated exhaust gave it a very rakish and appealing look. However, it was very similar in styling and price range to the 750 Shadow and Honda elected to have only one cruiser bike in that class, thus the reason for its short model life.
The CX650ED or Eurosport was also introduced in 1983 and was cosmetically very similar to the CX500 Eurosport produced to previous year. It was aimed at the UK, European, Canadian, and Australian markets and is really a superb motorcycle. The brakes, suspension and handling were far in advance of the CX500 variants, except for the Turbo of course, with which it shares many common features (TRAC anti-dive forks, Pro-Link rear suspension, twin-pot brakes and disc front and back. Unfortunately this model was not sold in the US although some have been imported by private owners.
In 1983, the engine of the CX500 Turbo was bumped up to 673 cc which meant an increase from 77 to 97 horsepower, making it one of the more powerful motorcycles available that year. In addition to the increase in displacement, the compression ratio was increased while the maximum boost pressure was lowered, making for a less abrupt transition from off-boost to on-boost than was present in the earlier CX500 Turbo. The fuel-injection control system was substantially revised for the CX650 Turbo, and the rear shock received an update as well by adding a manually operated damping control mechanism. Cosmetically, the CX650 Turbo differs from its predecessor primarily in color and badging. However, in a cost cutting exercise, Honda manufactured the 650 Turbo fairing from ABS plastic as opposed to the 500 turbo's GRP. A total of 1,777 units were manufactured and distributed mainly to the United States. The rest were distributed around the world but not sold in the Australian market.
With their complex fuel injection systems and related sensors and actuators, the CX Turbos carried high prices and were a nightmare for shade-tree mechanics. And while spiraling insurance rates were affecting all performance bikes, many insurers looked unfavorably at turbocharged models in particular, assessing them with exorbitant premiums. So although the whistle of the turbo and resulting kick of acceleration boiled the adrenaline of those who rode one, the CX650 Turbo—along with the imitators that soon followed—sadly suffered a premature extinction.
The Japanese and European market saw 400 cc versions of the CX and GL, aptly named the CX400 and GL400. In Japan the GL650 SilverWing Interstate was released as the Limited Edition GL700 Wing Interstate, although it used the same 674 cc engine that was used in the GL650. Also in Australia, the 1980-1982 CX500 'standard' models were known as the "CX500 Shadow". This made for much confusion when Honda released the VT500 and VT750 Shadow in 1986.
Influence of CX design
The CX series motorcycle has had an influence on the design of Honda's successful ST1100 and ST1300 Pan European models. These also feature transverse, or "flying V" engines and shaft drive, although they have four cylinders, fairings and luggage. Early influence for the CX engine design is believed to have come from the Marusho Lilac motorcycle where it is rumored that engineers went to work for Honda when Marusho finally went bankrupt in 1967.
- "Honda Motorcycles - A Five Decade Journey". http://motorhelmets.com/htm-service/resources-motorcycle-articles-honda-history.htm. Retrieved on 2007-08-31.
- "Moto Guzzi V50 Monza review". BikePoint. http://www.bikepoint.com.au/portal/alias__bikepointau/tabID__5760/ArticleID__118663/DesktopDefault.aspx. Retrieved on 2007-08-31.
- 1978-1982 Honda CX500, Motorcycle Classics, March/April 2008, http://www.motorcycleclassics.com/Restoration-Technical/2008-03-01/Honda-CX500.aspx, retrieved on 2009-02-25
- The CX-GL MCC (UK)
- Turbo Motorcycle International Owners Association
- Honda Gallery-CX650T Turbo
- Rob Davis' web resource for Honda CX technology
- The Australian CX500 CX650 Register