RestoCycle How-To: Rebuild your CBX Alternator

[NobleHops]

Intro video:



By now I'd guess that most long-term owners of CBXs have experienced problems with their charging systems, particularly those with the early model 79-80 twin-shock CBX. There are several factors external to the alternator that can negatively impact the performance of the charging system, including cruddy contacts in the ignition switch base, corroded spades and sockets within the connectors that carry much of the current the bike uses, and melted wires and contacts at the notorious 2-wire red connector that feeds charging voltage back to the battery. To holistically service the bike and the charging system for a long-term fix, ALL of these items should be addressed, but at the end of the day the heart of it all is this alternator, and if its not operating properly, nothing else you might do is going to restore proper system performance.

A persistent myth is that the CBX will not charge the battery at idle, and it's just not so. With the alternator operating properly and the rest of the weak spots in the harness addressed, I've seen 13.5 charging volts at the battery at idle, and 14-14.5 at 2,500 RPM and above, once the bike and the charging system components are warmed up, and none of it is particularly hard. See my other tutorials on cleaning the ignition switch base and recrimping wires and connectors.

Here's the patient for this tutorial, an original alternator from a '79 Honda CBX. Like so many of these, this one was working poorly, and measured 11.5 volts of output voltage at the battery terminals at idle. At anything less than 12.8 the battery is discharging, and that is also indicative of lower output at higher operating RPM, which causes any number of problems including weak spark, dim headlight, plus it's not good for the health of the battery. Modern AGM batteries that many of us use in our old motorcycles require a higher charging voltage, 14.5 would be ideal, and without it, they lose capacity and die a premature death. This can and should be fixed.

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[NobleHops]

Flipped over we see one of the interesting features of these alternators - they are not direct-driven, in fact they are driven through a 2-plate wet clutch system. A 1mm orifice at the end of the alternator drive shaft furnishes pressurized oil in between the two clutch plates to cool and lubricate them on this "wet" side of the alternator. Honda (or possibly Hitachi) made a manufacturing error on these though, and the other side of this clutch was manufactured incorrectly, and the drive plate is conical, by .002 as measured on a NOS part we have.

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By the way, this design of a standalone alternator driven by a shaft is in fact NOT unique to the CBX - the Yamaha Secas of the early 1980s used a nearly identical setup, with a clutch driven alternator located behind the cylinders.

OK, we're going in! There are 6 long screws visible on the cover - 3 of them secure the alternator to the crankcase, sealed with a square-section o-ring, and the other 3 are shorter and hold the two halves of the alternator together.

[NobleHops]

This is nearly everything you might need to do a complete job, although it is possible that you may also need a new rotor or even a $tator heaven forbid. We'll go step-by-step and measure as we go through it. All of these bearings and the seal can be found at your local bearing and seal store and will work perfectly well, but you can never go wrong with the Honda parts either.

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These are the bearings that are used. The first 4 numbers refer to the size and type of the bearing (6201, 6203), the other segments refer to seals on both sides, and other specifications.

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Here's a bearing-store seal - not the exact dimensions of the Honda part, this is a little skinnier, but works fine. As with the bearings, the Honda parts are still available and reasonably priced, so that's an easy option too.

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[NobleHops]

This is a set of carbon brushes for the "dry" side of the alternator, these pass current furnished by the combo regulator/rectifier to the slip rings of the alternator's rotor. In this design, the energized rotor is the "field coil" of the alternator - the alternator output is varied by how much or little the rotor is energized. As a result, these contact surfaces, and the condition of the rotor itself become really important to the proper function of it.

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There's your gasket, this one is NLA from Honda and so this is NOS, but not to worry - Cometic reproduced these and they are available from Tim's CBX and also thesupersportshed.com in the UK.

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Here's your (larger) square-section 0-ring that seals the alternator to the crankcase, and beware that these are for the moment becoming rare. The smaller oring sits just behind the bearing on the wet side of the alternator to seal the shaft - don't fail to replace this, it is important in keeping things as clean and dry as we want them in the dry side. The odd-looking rubber part upper left is a new replacement alternator wire sealing grommet, and if you're lucky you don't need one because installing it is a fiddly PITA. Finally the center metal shim is called an "arbor shim" and can be found in 10-packs from McMaster Carr, or singly from our friend Mike Nixon at The Motorcycle Project. That's actually an SAE-dimensioned part, but it works perfectly to shim the alternator shim, and is about 1.5mm thick, which is often just right. More on that later.

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If we have a "secret weapon" in this process, this is it. We'll show more of this later, but these are the two halves of the drive clutch setup. The grooved plate at the right is the splined "A" drive side, this mates up with the primary shaft in the engine, and pressure to its mate at the left is provided by a single spring that sits between the plate and the shaft. We'll talk a lot more about these parts later, and how to possibly refurbish yours yourself if they are not too far gone.

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[NobleHops]

OK, on to disassembly. The three screws are out and the alternator inverted and then the center section at right is lifted off of the cover, containing the stator and the brushes. First look at our rotor - not too bad, definitely not the worst we've seen.

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This is one of our spare rotors, after some quick resurfacing we did in house. We usually send batches of these to our machine shop pal along with a spare shaft, and he chucks them up in his lathe using the shaft to hold it, and then he machines them as little as he can to restore a perfect flat surface. We did this one similarly, but chucked the alternator driveshaft into our drill press, and smoothed the surface with emery and then fine wet-dry paper.

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The cover and the stator (stator = stationary), and the brushes. Let's look closer:

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Normal wear for the brushes, the one on the right is worn more than the left, as it rides on the much larger outer slip-ring. In a parking lot mid-tour, put these right back in and ride home, but during deep service these are ready for replacement.

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[NobleHops]

This brush holder is part-and-parcel with the stator, and so it needs to be unbolted from the cover to remove it all together. Take note of those two spring washers beneath the bolt heads, you do NOT want one of those bolts backing out and causing mischief after we put this back together.

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Hallelujah, our wire grommet is in excellent condition, and so is the braided sheath. These are as prior, a PITA to replace, but if it is badly cracked and shows signs of prior leakage, you really will need to do it. Replacements for this can be found at Tim's CBX (www.timscbx.com) in the USA, or from Six Center (www.sixcenter.nl) in the Netherlands. The braided sheath if needed can be found at Vintage Connections. www.vintageconnections.com

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OK brush holder is unbolted, and now the grommet is wiggled free and carefully slid out of the cover with the stator and brush holder for inspection and service.

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Cover at right, all that remains is to extract that bearing.

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[NobleHops]

Onto the rest of the disassembly, next we need to get the un-grooved "B" clutch plate free of the rotor shaft so we can extract that from the alternator base. This can be tricky to do without the grunt of a powerful air (or electric) impact, takes 2 seconds with it. Not shown: my other hand, holding the rotor on the other side of this cover with a rag, because I only have two hands and the other was holding the camera .

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Push the rotor shaft in till flush with the "B" clutch plate and then the B plate is easily removed. Then push it back so we can get the little oring off .

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With the nut and washer and "B"' plate removed from the shaft, now reach in there and extract this oring, it will make removing the rotor shaft from the bearing and housing easier. Remove the rotor and shaft.

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Almost there!

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Pry up that seal - carefully. Don't gouge the seal pocket with that sharp pointy screwdriver! Flip it over.

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Remove this bearing retainer. These can be Good and Stuck, possibly with thread locker. Heat is never a bad idea (wearing gloves when the torch comes out is a Good Idea).

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An old-fashioned hammer-powered impact driver with a really good fitting tip will make short work of those screws, and an electric one will usually do the same, just be very measured with an electric - short whacks on the trigger is safest, along with a very tight-fitting bit.

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Retainer off, next we'll extract this bearing.

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[NobleHops]

This is a thin and potentially fragile casting, which might make it more prone to damage if we whang on it carelessly extracting that bearing, and so a little heat is a good idea. After 30 seconds moving the torch around the bearing pocket it taps out very easily.

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Halfway home...

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On to the bearing in the cover, where we'll use the same technique - 30 seconds moving around that center protrusion with the torch. Notice that the cover is sitting on a twice-folded towel.

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As quickly as you put down the torch, pickup the (burn-you-hot) cover with a gloved hand or a towel and then WHANG it down nice and flat onto the towel on the counter. If you are lucky and can muster the strength and speed of Kung-Fu...

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...the bearing (at right) will be ejected. Hi-YAA!

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Or just use a blind bearing puller if you don't know kung-fu.

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[NobleHops]

Back to the air impact to get the rotor off the shaft. NOTE. Measure the rotor BEFORE you remove it from the shaft. If it measures in spec and you can get the slip ring surface nice and flat in a drill press or lathe then you DO NOT need to remove it. We're showing it assuming you do need to replace it, so you know how it comes apart.

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BZZZT, nut and washer are off.

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Now the rotor is in the press, and that's the only way to get this off without damage to the shaft. Use a press.

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But put this or something like it just below it, as it's going to let go suddenly and go flying if you do not.

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pump pump pump BAM. Rotor now free of tapered shaft.

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[NobleHops]

Clean it all up!

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That's better!

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We love the ultrasonic for cleaning up those electrical connectors. We use a very slightly acidic Crest cleaning agent called Citranox in deionized water for electrical parts.

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Nice and clean, those terminals look like new pennies in there.

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Into the parts washer to clean you guys up.

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[NobleHops]

Alright, with everything apart and clean, now I can move onto inspection. Here's our "B" clutch plate. Grooved and work-hardened.

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That's a refurbished one to the right. Better .

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The "A" plate actually fares worse - that's the one with the manufacturing problem. It begins to wear with contact only on the outer 5mm of the plate, and then it slips and heats and wears and eventually grinds its way into a semi-flat surface in full contact with its mate.

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This is one way we know this - this is the alternator and A drive clutch from my personal '82 CBX, which had a scant 10K mikes on it when this was disassembled. The crosshatch from manufacturing is still plainly visible on both parts, and untouched on the center of the plates.

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This is another way we know this. At left are two unicorn horns - NOS Honda A and B plates, pure unobtanium.

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...and there is a .002 feeler gauge, indicating the problem. This can be fixed! And if it's not too bad, you can quite possibly DIY too. See less

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[NobleHops]

First you're gonna need a big bowl of Wheaties, and maybe pop of couple of preemptive Ibuprophen too. That's a big giant sheet of emery paper atop our granite flat block. You can substitute a sheet of 1/4 or thicker plate glass, and the biggest sheet of sand paper you can find, but it really does need to be Flat. Grab that clutch by the stem and start making figure-8s on the sand paper. A few thousand figure-8s.

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Almost there. when the sanding marks are equal across the entire plate, you're done, and your shoulder is SORE.

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Do both, they wore oddly together. No shortcuts! This plate was manufactured flat unlike the other, this will go much faster if it's not too bad for starters.

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When you're all done, take a small file or a Dremel and chamfer the edges of these oil flinger gooves, so they don't overheat and tear up the surface of the B plate as they wear in together.

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If you're starting like this, you're going to be there for a WHILE, and I'd advise you to have this professionally ground. Machining is not ideal for resurfacing this, this needs professional grinding when it gets this bad, and it ought to be cooled as it's done too. TrueDisk.net does these for us.

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OK, everything is clean and ready for refinishing and then reassembly.

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[NobleHops]

First we're measuring the resistance with the DMM across the two copper slip rings. The manual gives us a spec of 3.5 - 4.5 ohms, and this will vary with the temperature of the part - higher temperatures = higher resistance, so anywhere in there is OK. This rotor is perfectly good, it just needs a little resurfacing of the slip rings so the brushes will make perfect contact as they wear in. If this measures outside the range provided in the manual (and you're not measuring a very cold part in an icy garage), then it's time to see our friends at Rick's Motorsport Electrics, or Bob Franzke of CBX Performance for a rewound replacement.

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Here's our "A" drive plate as it is assembled, for reference. At the top of this stack is a special washer that keeps the spring square and centered and that's important. This may get left behind when the A plate is removed from the engine, so keep track of this.

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There's the entire ORIGINAL stack, left to right - centering washer, spring, thinner steel washer, thicker plastic/fiber washer, "A" drive plate.

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Difference between the thinner steel washer to the left and the thicker fiber washer to the right.

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This is wearing, but still OK, and unobtanium. I have a few of them if you're stuck. See less

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Measure the spring with vernier calipers - this is one of the critical parts that causes problems. Heat and time and constant pressure causes these to lose some of their free length, same as clutch springs can. The free length of this spring when new is 31mm, and this one is about 1.5mm shorter than that. When new there is about 6mm of total spring preload when the alternator is installed and that is important to restore. This is the purpose of the shim we showed above - to restore the proper preload on this spring as it holds the two drive clutch plates together, to reduce the slippage and heat and wear. If yours is much less than 28mm, then it's time to hunt up a replacement, from eBay, or Louis Mintrone of usedcbxparts.com, or TheSuperSportShed.com.

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We buy these steel arbor shims by the baggie of 10 from McMaster Carr, but Mike Nixon from themotorcycleproject.com will sell you one singly for the princely sum of a few $. These are pretty much ALWAYS needed.

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Here's the shim that we use, 1.5mm, just right for our 29..5 mm spring. We keep a 2mm shim in stock too, in case it's needed.

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[NobleHops]

OK, our stator and brush holder is now very clean and ready for inspection, let's see what it shows:

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Honda wants us to start the bike and warm it up, and then remove the 6-spade connector to make our measurements, but that ship has sailed already . We can still check this out with the help of another pair of hands, and some inference.

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Remember that we cleaned this connector spotlessly in our ultrasonic cleaner BEFORE we made these measurements , you don't want to be fooled into buying a $300 stator because you were measuring resistance through dirty terminals. We're now measuring each of the three yellow wires of the stator windings to each other, measuring ohms (resistance). The spec in the manual is .4-.5 ohms, warm. We've got .4 across all three combinations as you will see, with the part cold (would be higher if the part was warmed up as specified). Pair 1...

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Pair 2 (look at the tips of the probes) - A-OK

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Pair 3, A-OK. Onto the tests of the brush holder and rotor combo.

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Here's where we're improvising a bit - Honda gave us a spec for the total resistance across the black/white pair of wires in the connector when the stator is installed with the brushes in contact with the rotor, so Alex is holding the brush holder in position against the rotor while I measure resistance. 11.3 ohms and the spec is 10-12. Stator is fine, Yaaaay!

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[NobleHops]

Random photo of the parts we're replacing. These two clutch plates will go into the pile to be sent to Tom for resurfacing, and if they were the last ones on earth, both the paper gasket between the alternator halves and the square oring that seals the wet side to the crankcase could have been reused. Bearings were also OK, and if you get into yours and you are not refinishing, you may elect to just sail on with those. The cover bearing is the one that is more likely to have problems - it is smaller and carries less lubrication, and that cover can get HOT, especially as the clutch plates wear and create excessive heat. We would say that ought to be replaced for good measure during service, and the other bearing is less urgent.

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Side track - different alternator. We serviced one recently and noticed that the stator would not be properly clamped when the cover was reinstalled, and was rattling around in there. 5 minutes lapping stray powdercoat fixed its wagon, but it's a caution - if you're using thick coatings like powder coat or even paint, be sure the stator is clamped and not rattling when you reassemble.

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OK, let's refinish! If you're doing a '79 CBX alternator then it’s important to note that the cover to the left is made of magnesium, and cannot be polished or left bare. Magnesium is neat stuff, strong and lightweight, but is is also reactive to air and will discolor. It needs to be sealed. If we're refinishing to match the crankcase during a restoration we will paint it the same as we paint the crankcase - in this case using the excellent Duplicolor "GM Silver". The 80, 81 and 82 covers are made from aluminum alloy, same as the alternator base, and so there is more flexibility in refinishing those, they may be painted as shown, powdercoated, polished, etc. This stuff gets a lot more durable if is allowed to cure for 24 hours and then baked for an hour at 200 degrees.

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Another item to check, this is the primary shaft that the alternator is driven from, and as shown the special centering washer got left behind when the alternator drive plate was removed. Note also the 1mm orifice in the press-fit plug at the end of the shaft. it's worth ensuring that orifice is clear and that the plug is in there. On one recent project it was missing altogether and that resulted in oil POURING into the alternator wet side and that no doubt resulted in reduced oil pressure further down the line where it is urgently needed to float the cams and crank in a film of pressurized oil.

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Installing the bearing in the cover - this is most easily done if the cover is heated to 200 or so ahead of time, and the the bearing pocket and the bearing are lightly greased. If you get jiggy and give the bearing a few hours in the freezer too it will nearly drop into place. Don't go nuts with the installation grease, just enough is just right, and clean up any excess before you close it up.

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Headed for the oven and looking handsome anew.

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