So as I am sure you already know or will soon find out that the alternator on the CBX is its biggest Achilles heel, the alternator itself is a fairly common design and is reliable contrary to popular belief, a number of its fellow models and contemporaries also used this design in 1979 without issue. This issue revolves around its drive system which employs a pair of steel clutch plates, these clutch plates wear for a variety of reasons (not for this knowledge base), however a key one you must check is the oil restrictor, this either comes loose with the oil pressure pushing it against the alternator shaft restricting lubrication and cooling or secondly, it also can block at the rear as shown in the photo so please ensure you check this by starting the engine with the alternator removed (ensure all the usual safety checks before doing this have a pot ready!), it takes around 2-3 seconds for the oil to transit the restictor if no oil appears try clearing it with a 2mm drill (its 10mm deep).
Lack of lubrication on start-up and/or blocked restrictor causes the clutch plates wear-causing galling resulting in significant loss of to drive the alternator, this causes major heat issues due to friction (I have seen plates that have gone red hot) and melts the plastic nylon 6 thrust washer on the rear of the A plate. The friction on the B plate transfers down the rotor shaft and causes the oil seal, bearing and rotor windings to fail. With light galling they can be lapped on a surface plate with emery paper, otherwise, they can be refurbished by The Super Sport Shed by sending them to us and using the order page in the shop here https://thesupersportshed.com/product/cbx-alternator-clutch-rebuild/ , however, please send us pictures first to firstname.lastname@example.org so we can evaluate them first before ordering. If you are in the US or Canada CBX Performance provides an exchange service here https://cbxperformance.com/products/ols/products/alternator-clutch-plates-a-b-custom-upgrade-send-us-your-cores We also recommend if significant galling/wear has taken place to remove and clean the oil pan and check and remove any residual deposits from the oil pan and strainer.
Alternatively, you can purchase the kit in the online shop here https://thesupersportshed.com/product/cbx-clutch-friction-plate-kit/ if you have access to the machine tools to machine the plate yourself. Machining of plates should only be undertaken if the plates are scoured beyond lapping on a surface plate or piece of plate glass. Both plates have been hardened using induction or case hardening to a depth of around 0.75mm, below this depth the material is soft and will wear at a very fast rate if you machine/lap below this hardened surface, plates that are not worn are very difficult to machine and break through the hard layer. The drawing is below to undertake this process yourself, we do not warrant this process and it is undertaken at your own risk.
The other issue is the spring length, this needs to be a minimum of 29.5mm to avoid slippage and reduced charging (and galling to the clutch plates), in addition, check that both the plastic and steel thrust washers are in place behind the plate and spring as quite often I find either the plastic or spring steel thrust washer missing which we can supply if you go to the order page on the shop here for plastic https://thesupersportshed.com/product/cbx-alternator-thrust-washer-vesconite/ and here for the spring steel https://thesupersportshed.com/product/cbx-1000-alternator-steel-thrust-washer/
As mentioned, the alternator electrically is similar in design to most Honda's and its contemporaries of that era, if it fails to charge the following needs to be checked beyond the clutch plates which are the first thing to be examined on removal. The tests below will be the same on the CB750/900/1100.
These are easily examined by removing the front casing once the alternator has been removed from the bike, to do this unclip the 6-way connector behind the right-hand side panel and tie a piece of wire to the plug so you can pull it back through on refitting. Remove the three bolts that attach the alternator to the engine casing (10 o'clock, 2 o'clock 6 o'clock) If the front casing does not easily come off after removing the 3 bolts apply heat using a heat gun to the centre of the case where the outer bearing sits, it should drop out after applying heat. The brushes once the casing is removed are clearly visible and should be in excess of 6mm above the brush holder, if not replace them (hopefully no explanation is required here on how to do that). Be very careful when refitting the six bolts not to overtighten them as the casing easily cracks if they are overtightened. These can be purchased here online https://thesupersportshed.com/product/cbx-1000-cb-750-900-1100-alternator-brushes/
The rotor needs to be checked for open circuit or short circuit/low resistance. You will need an ohmmeter/multimeter set to the low range (normally 200 ohms). Measure across the two copper slip rings, you should expect to see a resistance of between 4-5 ohms both on the US and European variant of the alternator. The alternator will work quite happily at 3.5 ohms but will have reduced performance and will likely fail at some point in the not-too-distant future. Also, note that the resistance can drop right off when the bike gets hot, you can check the resistance through the white and black wire in the 6 way connector.
The three windings on the stator (three yellow wires going to the regulator from the red connector) need to have a resistance of between 0.3-0.5 ohms. If all of these check out it is likely the problem will be in the regulator/rectifier or the wiring on the bike. If you are not confident to undertake this yourself find an auto electrician who can check this out for you. Whilst you're at it checking out these measurements with the red connector apart (behind the RH side panel) check for corrosion and dry joints as this can be a common problem clean and re-assemble.
I have come across numerous regulators that have been purchased in the hope it will solve the charging issue, normally it is either the galled clutch plates/short spring missing thrust washers, worn brushes, burnt out rotor or a combination of all of them (which is quite often the case!), after doing dozens of alternator rebuilds the stator rarely fails. In this article, I will not explain how to test the forward and reverse bias of the diodes in the regulator as it is described in the factory manual and can be found easily found on youtube https://www.youtube.com/watch?v=-2jWIkhy1fo