Well, I bought my CX500 last autumn and right away I found very good and informative web-pages cx500 forum. I didn't stay away from the site reading as much I could all possible aspects of that great bike! Little by little I found both the mechanical and electronic aspects what should I consider while repairing my bike. The am. forum is one of the bests I have ever found! Forum members are giving willingly good advice for novice ppl like me. Perfect. You are not pushed away no matter what you ask. It's like to be at home. :)
Very soon I realized that CX500 bikes are still very common and sought-after. Even if all they start to be over 30 years old bikes. 496cc water cooled V-engine gives nice rides and surprisingly well and easily you will find spare parts! I think I do not waste anybody's time starting telling the cx's the most common mechanical weak points cause you can easily jump on the cx500 forum and just start reading about the bike.. Well, maybe it's better to summarize those things though:
- cam chain and it's tensioner
- water pump mechanical seal
- stator
These are maybe the most common reasons you have to stop riding your cx. These three things are normally changed in the same time, so the name "triple bypass". All these things need the engine to be dropped. Period. Okay, the water pump mech. seal can be changed the engine in the frame. It's called "Shep's method" according to one the most experienced cx riders and method inventor. Of course, other things can fail in your cx, for sure. It's a mechanical device. CX500 is also known to be rather sensitive to produce tapping and ticking noises. Rattling noise is also very common for this bike. Owners recode videos for others to listening. I cannot blame. CX does have push rods and that way many gaps to be adjusted right. Not speaking of wears and tears all over the engine. Well, I have listened those odd sounds many times too. :) In spite of all those mechanical aspects Honda CX500 is really a nice bike to ride and the engine has reached in many cases many, many miles.
Well, after studying cx's mechanical points and got the bike working well you might face problems on the ignition side. Yes, there is numerous cases that hobbyists have all sort of problems with bike's electrics. Old fuses are kaput or there is a bad connection in one of the many connectors. All this is typical with a bike in this age. Maybe the best you can do your cx ignition is to replace the both ignition coils and spark plug caps. They are very cheap and at least take away a few malfunction points of the bike. Spark plugs are commonly available, no problem. Well, in the end you may face the situation your old ac-cdi unit under the seat is the problem. The AC-CDI unit gets it's name from the words Alternating Current - Capacitor Discharge Ignition. The original stator inside the back cover of the cx's engine has two extra coils which produce about 115 VAC voltage to power up the cdi unit. AC-CDI unit could also be called as analog cdi unit because inside the box is just active and passive electronic components. No microprocessors as in many cases nowadays. What the ac-cdi unit do then? Of course, it finally produce a spark to the spark plugs as a final product but before that it has to handle quite many tasks. Here is my explanation for the different parts of the ac-cdi unit and the auxiliary devices:
"Both cylinders get sparks constantly 15 degrees before TDC from idle to about 2000 rpm. After 2000 rpm advance pulses amplitude rise and cross over the triggering level of the thyristors and begin to be dominant. When engine speed rise more (>2000 rpm) the front edge of the advance pulses cross over the triggering level earlier causing ignition advances. Now the advance angle rises more or less linearly with a rising slope to 37 degrees before TDC at the engine speed 5500..6000 rpm. At the point of 37 degrees BTDC also the pick-up coils negative pulses mix causing the advance angle won't rise anymore. So, the max. advance angle stays at 37 degrees up to the red line area. On the red line area the left side small thyristor (SCRP) cause the advance pulses go to the ground. (Note idle positive pulses still trigger the thyristor discharging the capacitor but advance is not right on the left side.) No more higher engine speed with only the right side cylinder's correct advance. If revs drops under that the left cylinder comes back in the game because advance pulses can trigger again.
Two thermistors keep the advance curve the same regardless of ambient temperature. Otherwise the advance curve would change it's starting point according to temperature. No good!"
I copied the text from my Flickr-site with the photo:
As we see there is just capacitors, resistors, thyristors and thermistors. All those components have their specific duties and in this point I think it's worth of mention that originally Honda has made fantastic job. In the end of 70's with those time electronic components they made an analog ignition unit which really works fine. No matter is it hot or cold climate the unit can produce steady advance curve for different revolutions of the cx's engine! I think now we are in the heart, the soul of the bike!! In order to make the unit work really well is not easy. Well, in that point of view, at least, I appreciate their work. But eventually you come to the point that nothing is ever lasting. We have to remember that an electronic unit which has worked well over 30 years is awesome work.
Well, after buying my bike I became aware of that some day I might face a situation the old ac-cdi unit won't work anymore. So, I started to figure out would there be a possibility to build own replaceable ac-cdi unit? After digging out many, really many writings and forum threads I came a conclusion it really is possibly. There simply is nothing special or invented-thing in my unit! If you have designed and made your own electronic boards you will find out what it is all about. Just try and you will find it! :) Okay, I add here a video of my testings of the cdi unit.
Well, that's all now..more to come..
