Honda CX 500 ~ Cars and Bikes
Cars and Bikes

Saturday, 26 January 2008

Honda CX 500

Actually I can write a lot of articles for Honda CX 500 1980 , I bought it 12 years ago and for the last 5 years this bike sit in my garage with several electrical problems with it. However this is the first article, which some of it I compiled from several sources. I also post a CX500 wiring diagram in this link.

Before I bought the bike, I saw some pictures in the internet like this:

And the shiny rare shape engine and big and strong looks rear wheel like this:

Those above pictures so impressed me and decided to buy one. In my country this Honda is very rare, may be only 3 or 4 of them. Up to date the bike still have the original shape like this:
and this is the engine:

This motorcycles have electrical problem and sit silently in my garage. When it run normally, the bike is smooth, easy to handle, almost maintenance free, and quite powerful. The problems mostlikely came from my "home made CDI", which was made around 11 years ago. I found the "simplified" CDI circuit diagram from the internet, however I lost the original diagram, and I can't find it anymore from the internet. My first home made CDI works well for 3 years and I made a second one which only can works for 2 years. And the second promblem probably cause by my stator/alternator. The pictures below showing my " home made CDI" and the advance pulser. I'll post more information about DIY CDI in this link and this.

So for next few weeks I will keep my eye on ebay, looking for some selling CX500 CDI (I think around 50 to 100 US$) and also probably a "new" or re-build stator/alternator (this one is quite expensive arond 250 US$). Hopefully this bike can run again only with "new" CDI, because the stator still away to expensive for me. Oh, ya other thing is actually my cx is not real cx500, in the engine number is written CB450 ........, I have no idea about this, probably a japanese version of CX series.

Honda CX500 History:
The Honda CX series motorcycles 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 carburators 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. 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 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".

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. 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. 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.

Wheels and Chassis
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 GL650I and Turbo) were equipped with a single front disk brake whereas all other bike posses 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. 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. If difficult to find the original seal, alternatively can use
Yamaha Mechanical Seal part no 11H-12438-10 as written in Rob's site. My CX had the same problem, and I went to "seal shop", then find a same (almost) size seal for the replacement, this seal have no brand, however at least this seal works for 3 years before the electric problem arise.

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). In the US, the 1983 CX650 and GL650 have an automatic cam chain tensioner that never needs adjustment. 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. For more detail about
cam chains adjustment and changing please visit Rob's site in this link.

Finally, the CDI boxes on 1978-1981 CX500's 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 O.K., but prolonged high speed operation could eventually make them shatter, usually destroying the radiator and spraying coolant on the rider's leg.

CX500 Turbo
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 Z1R TC was the world's first turbo-charged production bike.The Cx500 T 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 engine deliver almost 78 hp, no other bike in this engine capacity can produce more than 55 hp at that time. 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 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.


1. Rob Davis site: excellent cx 500 source, Thanks for Rob dedicated for cx500, it is really useful for CX owner. You can find all history, technical tips, how to pages, and numerous links related to CX500.
CX Site
3. CX500 wiring diagram


László Oszkár said...

Hi CX biker brother!

As I understand, you have problem with the CDI unit. Fortunately(or unfortunately) I have one in spare. I bought a complete motorbike for spare parts because my crankshaft "died". Lat's make a deal! I provide to you the orig. CDI and you help me to purchase a new crankshaft(and bearings and maybe the con.rods). I am from Hungary, and here is not so easy or sometimes imposible to get parts for old bikes.

Anonymous said...

Can you post the schematic you used to create your own CDI?

explorer said...

Ok, I will work on it and post it. I'll digg my old data. Actually I follow an article written by Goerge in NC, It is an old file. Please check my blog next few days.

konikt said...

Hi where you found these photos??"Before I bought the bike, I saw some pictures in the internet like this:"

Tina said...

Hi there,

I recently bought a CX 500 Custom in original , very good shape. The bike has 32.000 km and is a 1980 model.
There are 2 details that concern me. 1.) Starting it up it will run on one cylinder until it is warmed up a bit. Should I just change the spark plug and see?
2.) On the left side above the Starter motor there is some cooling fluent leaking out. I can not see where it is coming from but it does concern me?
IS there a drain hole under the carburetor where this fluid is coming out or is the seal to the water pump broken and that causes the leak?
Thanks for your comment .

Great site and a great bike too.
Thanks Richard Sander
Courtenay / Vancouver Island / Canada

Richard said...
This comment has been removed by the author.
Richard said...

Hi there,

I recently bought a CX 500 Custom in original , very good shape. The bike has 32.000 km and is a 1980 model.
There are 2 details that concern me. 1.) Starting it up it will run on one cylinder until it is warmed up a bit. Should I just change the spark plug and see?
2.) On the left side above the Starter motor there is some cooling fluent leaking out. I can not see where it is coming from but it does concern me?
IS there a drain hole under the carburetor where this fluid is coming out or is the seal to the water pump broken and that causes the leak?
Thanks for your comment .

Great site and a great bike too.
Thanks Richard Sander
Courtenay / Vancouver Island / Canada

Anonymous said...

Hi great blogg

can any body say if it`s posible that the cdi unit are to blame my bike are running on one cyl up to ca:2500-3000 rpm


rhino said...

Hi. I also bought myself a CX500C. It is really a nice bike. But when I tried to start it. Then all of a suden it did not want to start. Does any body know what it can be? I cleaned the spark plugs out. But still nothing

rhino said...

Hallo. I bought myself a honda CX500C. Its a nice bike. Also as neat as it can get. But when I tried to start it tonite. I didn't want to. I heard a little back fire from the one exhaust. I cleaned the plugs but still nothing. Can anybody give me advice?