Alternator rotor, stator, brushes.
Brush and/or brush spring changing, etc.
Rotor removal WARNING!
© Copyright, 2017, R. Fleischer
Skill level required for most any work on these items: Non-ham-fisted Beginner or better
Rotors and Stators:
This has been a confusing subject to many. Anton Largiader's website article, with its text & photos, will explain explain some things slightly differently. I have minor disagreements with his article, but ....it does have some useful information & has some photos you might want to look at. See Anton's article here: http://largiader.com/articles/charging/.
I have the most detailed and pertinent information below in my own article.
The original /5 bikes had a 180 watt alternator ...with the stator assembly end that fits into the motor timing chest cavity being 105 mm in diameter. Some 1974-1975 Airhead motorcycles, & possibly a few barely into 1976, were made with the 105 mm engine cavity. Those had 280 watt alternators, easy to identify as they had the extra stator electrical terminal. This means it is possible to upgrade a /5 from its 180 watt alternator to a 105 mm 280 watt alternator with the appropriate parts changes and the parts will fit. These changes were stator & diode board and adding one wire, all at a minimum. If your /5 rotor measures ~7 ohms, which was the original value, then I recommend it be changed to a later rotor of ~3.4 to 4 ohms; the electronics VR is optional. All /6 and later stators had a center tap on the windings, & some small diodes were added to the diode board. If you do not use the /6 or later diode board, the output will be less. I suggest not using the last version of the Airhead rotors, which were ~2.8 ohms. For all other /6 and all later Airhead motorcycles, the cavity and stator were 107mm.
A short section of technical information, mostly a bit nerdy:
The original rotors of the /5 were 73.4 mm in diameter. Those were approximately 6.9 ohms and are usually just referred to as the 7 ohm rotors. In 1974, the center tap was added to the stator windings, the rotors now had heavier wire and 3.4 ohms, but still 73.4 mm. The R90S, ONLY, had a larger inside diameter for the STATOR. That stator assembly had a BMW part number of 12 31 1 243 003. NOTE the 003 number. The 002 was the stator for all other bikes (not the R90S). If you use the -003 stator, your maximum output is lower, & the curve of rpm at which output occurs is less steep too.
In 1975 or 1976, the ROTOR size was made slightly smaller, at 73.0 ...probably some bikes had enough crankshaft whipping to allow rotor to scrape against the stator ....., which the R90S STATOR was supposed to be the fix-for, originally. My guess is that BMW changed things so as to not confuse the rotors/stators, as with a stator inside diameter change, if used with a smaller rotor, would greatly DEcrease output; yes, it IS confusing. The STATOR HOUSING has the alternator number on it, and the Bosch number, for these 1975 or 1976 changes was 0 120 340 005. These have slightly lower low rpm output. No books nor other literature, AFAIK, describes these things, except this article you are reading.
Most of this nerdy stuff is a bit moot. The more important things (??) are that the stator part number on it & the fact that as you INcrease the air gap between stator & rotor, by means of changing the stator to a larger inside diameter, or the rotor by decreasing its diameter, or both, then the lower rpm charging suffers a bit, & the high end output could suffer some too. That is why the original R90S parts had less watts deliverable. NOTE that it is reasonably likely that on any given old Airhead, the rotor has been replaced at some time, and only careful resistance and physical diameter size measurements will tell the story. It is even possible for the stator to have been changed, still using the old case Bosch number. This can get nasty, the result being poor output....if the very last stator version and rotor version are used where they should not be. Complicating the understanding is the use of an Authorities alternator, which is actually a mix of alternator items AND uses an ~14.2 volt (as set by the factory) voltage regulator.
The final change came in the early 1990's. The rotor became 2.8 ohms, the stator had a change in resistance, now was 0.8 ohm sections, & the stator assembly is 12 31 1 244 641. The maximum output was a bit lower, but started at lower rpm. Mixing these parts with earlier alternators can result in output problems.
The result is that STOCK versions of ALL the alternators from the introduction of the /5 in December of 1969, to the end of Airhead production in 1995-6, was that output wattages could be 180, 234 or 238, 240, 250, 260, 280 ....and perhaps a few others, or some corrections are needed ...there is confusion on the real outputs ...and my values here include the Authorities (Police) versions.
I have data on this website from REAL testing, on a known perfect standard motorcycle & system, a 1983 non-Authorities bike that I personally owned & prepared. The article is at: https://bmwmotorcycletech.info/altcapability.htm There is a LOT of information besides the Bosch measurements; including extensive expansion of information, output-versus-rpm, etc. I suggest that you read it after you read the rest of this article, below.
The earliest voltage regulators were mechanical; designed for the early 7 ohm rotors, but mechanical regulators were used even with the next lower ohms rotors ....until BMW went to electronic regulators. The change to electronic regulators happened first in the nearly-same-looking, but shorter, Bosch metal cans. Eventually the shorter metal can VR was dropped in favor of the flat plastic VR box. The metal can regulators, mechanical or electronic, are all adjustable for voltage output ...and I recommend adjusting them, per articles on this website ...your battery will appreciate it ....so will your wallet, as the batteries will last longer.
For practical purposes, almost any combination of any of the alternator parts can be used, usually with either some improvement or some deterioration in electrical performance. With proper parts, the improvement is large, for the /5. The main restriction is the noted 105 & 107 mm situations, although if anal enough, you could exchange the timing chest cover (which I do NOT suggest). I also suggest NOT trying to bore the 105 hole for the 107 mm stator. Anton's site has photos of the two, and there is a way to recognize them without measuring them.
THE LAST OF THE ALTERNATORS WAS RATED AT 240 WATTS. It uses the changed stator & changed rotor windings-resistances & rotor OD & stator ID sizes of those, all as noted previously. These items may not play well with earlier items .....the result can be decreased output. You will NOT damage anything by trying combinations of whatever parts you happen to have.
CAUTION!! READ THIS BEFORE REMOVING THE FRONT COVER!!
BE SURE TO DISCONNECT ALL THE BATTERY NEGATIVE POST TERMINAL WIRES FIRST! If you have only one wire at the negative (-) battery POST TERMINAL, it likely goes to the stock place, which is the speedometer cable hollow bolt; if so, then you can disconnect it at that bolt & not the battery, if you prefer to. If you disconnect at the speedometer cable hollow bolt BE SURE the wire lug end can NOT contact anything (tape it, or put electrical spaghetti over it). The battery MUST be electrically disconnected; removing the negative wire(s) is usually the best method if more than one wire at the battery.
Only with the battery disconnected is it safe to remove the outer aluminum cover of the timing chest on motorcycles with the Bosch type of stock alternator diode board. Remove the outer timing chest cover, usually just two long allen screws (three on early models). There may be a locating peg at the bottom. Wiggle off the metal cover. If you have a pre-1979 model, be cautious about the rubber around the points cavity & the rubber grommet also in that area, & the tachometer drive, ....when replacing the cover. If you have a BMW oil cooler on your bike & the cooler is mounted above the top of the cover on a frame cross piece, you must remove the cooler first (two each 10 mm bolts & waverly washers, then wiggle the cooler out of the way). Remove ONLY the left & right 10 mm hex bolts and waverly washers holding the cooler to its bracket, thus leaving the bracket in place. If you have a faired model, you must remove the outer painted fairing plastic cover before you can remove anything else. Note the folded metal clips used as nuts ...be sure they are centered when you try to replace the plastic cover. The earliest aluminum outer covers did not direct as much cooling air to the alternator; can be replaced, and the same goes, especially, for the early NON-louvered outermost fairing models covers. That outer painted fairing cover originally was solid, later louvers were added, circa 1984. The louvers DO improve alternator system COOLING. My 1983 R100RT came with the non-louvered cover, and rather than replace it and then have to repaint it, I cut my initials, HUGE ones, with substantial air openings, into & through the cover so there were substantial air openings.
ROTORS REMOVAL ..............CRITICAL!
To remove the rotor, you must remove the stator housing first. Simply pull off the push-on connectors, unscrew the three long screws. Next, pry the stator away from the motor, but DO NOT USE A SCREWDRIVER, DO NOT PRY AGAINST THE WINDINGS. PRY A LITTLE BIT AT A TIME, ALL AROUND AT THE MOTOR CAVITY AREA. I USE A SMALL PIECE OF WOOD AS A PRY TOOL!
If you are removing & replacing a ROTOR ONLY A HARDENED BOLT REMOVAL TOOL should be used, DO NOT use a conventional fingered puller. You can make a tool to do this, but the tool must incorporate HARDENED parts that will be fitted inside the rotor during use. I highly recommend you only purchase the proper one-piece removal tool. It is available from BMW; and, aftermarket sources. I keep one in the on-bike tool tray, even though I no longer have the stock alternator that would require it ...after all, YOU want to help others ...riiiiight? I cannot over-emphasize this cautionary note. If the tool you use is not hardened, it WILL, or CAN BEND inside the rotor. THEN YOU HAVE A REALLY BAD BIG PROBLEM.
How the rotor normally attaches to the crankshaft:
The stock bolt that tightens the rotor to the crankshaft screws through the limited depth of threads of the rotor, that is, the rotor has an area of no threads. The end of this stock bolt screws into the threads inside the nose of the crankshaft. Thus, tightening this bolt pulls together the female taper of the rotor and the male taper on the end of the crankshaft. Since a taper fitment can transmit tremendous forces (a keyway and key is just one of other methods of coupling parts together), not much torque on this bolt is needed to hold the real power transmitting areas, those tapers, together. The tapers MUST NOT BE OILED, and in fact must be very clean and dry during assembly!
How the rotor is removed:
The rotor is removed, when so needed, by a simple method. The original stock rotor bolt is first totally removed and set aside for the re-installation later. The hardened special tool is screwed into the rotor, and it passes through the rotor as does the normal bolt ...but it additionally continues to engage the rotor's threads. There are no threads at the nose of this special bolt-tool, the nose of the special tool goes into the crankshaft nose without engaging the crankshaft nose threads. The tool is long enough to bottom-out on the bottom of the hole in the crankshaft nose. At this point, the special tool has its longish threads area engaged only in the rotor's threads. As you tighten the tool, it pushes against the bottom of the crankshaft hole. When the special bolt is tightened enough, the rotor will very suddenly pop off the crankshaft (so be ready with your other hand to catch it so it does NOT fall to the floor).
The critical part is the removal tool that, during tightening, is inside the rotor and going into the crankshaft nose. This tool must not bend. Never....ever! ..... use anything but the special bolt, or properly made-up hardened parts, to remove a rotor. I can NOT emphasize this enough!!
How the rotor is installed:
When replacing a rotor, the male and female tapers of the crankshaft & the rotor, must be 100.00% nick-free and 100.00% CLEAN & DRY ...not even finger prints! ...and do not use gasoline as a degreaser. Be sure the rotor end that goes into the rubber seal is not nicked, and it is smooth at that edge ....and clean that rotor area too, although it can be faintly oily to help protect the seal. Push the very clean rotor taper onto the very vclean tapered crank nose. Reinstall the regular bolt. Do not over-tighten the rotor bolt. BMW's tightening specification is too high, in my estimation. The official specification for the tightening of the stock bolt in the center of the rotor is 23-27 Nm, which is 17-20 foot pounds. I seldom torque them with a wrench, but I think that 14 foot pounds is OK. A locking washer is under the bolt head.
SO, despite all my cautions, you used a soft bolt or other tool, perhaps a soft two piece tool ...and you have bent the tool(s) inside the rotor?
Typically, the symptom is that your 'tool', will not pop the rotor off ....and probably felt somewhat 'giving' as it was tightened. The tool must normally be quite tight to get the rotor off. If the tool seems to bottom OK in the crankshaft, and then, instead of very little additional rotation to bring it to a truly solid feeling & then the rotor popping off, there is a bit of give ...and give ...and if you continue increasing force as you try to remove the rotor ...it just seems to 'feel almost-squishy-funny' ...until you worry about things ....well ....You are now at the GOTCHA point.
The tool has either bent or canted sideways depending on if one piece or two piece tool. It is even possible for one part of a dual-piece tool to be hardened, and not the other ...or, one part is too short or thin. Whatever the cause, you are now in very serious trouble. If you can, remove the bolt (or, two pieces you used) by unscrewing it. If you can get the bolt or pieces out, you are likely not in serious trouble ...just get the correct one-piece bolt and proceed.
Assuming the worst; you have, in my opinion, two choices, depending on what items you originally put into the rotor.
I would try the following first: Get a SLIDE HAMMER (see your local mechanic, ....) onto the bolt head if you can. You may find that using the slide hammer will remove the rotor, & you may even be able to remove the bent stuff inside the rotor and even save the rotor from damage. I would not be worried nor concerned about saving the rotor.
If the above method does not work:
Make up a very stiff, very thick, stepped steel plate that allows you to press it against the timing chest (without injuring the timing chest) & allows you to use a more-or-less conventional puller's fingers on the rearwards (motor end) surface of the rotor. The puller's bolt to pushes against the steel plate. There must be space between the plate and the rotor (very little is needed). It is a PIA to make up a stiff-enough plate to do this work. Be really careful ...you do NOT want to damage the crankshaft nose!
On rare occasions with a brand-new rotor, or a rebuilt one, or a rotor that was tested with possibly reversed polarity power source ...and you find that now the system will not charge at all; or, charge output is quite low, and you know the diode board is OK, etc.... you might have installed the wrong rotor resistance, or, there is another cause. Usually the situation is a total lack of charging, as shown by a GEN lamp that lights up, but never goes out as RPM is raised. You test things, & find nothing wrong. Because of this problem, I now recommend that any time you install any rotor, that the following tests and procedures be done.
(1) Test a new or rebuilt rotor with an ohmmeter before you install it. Be sure that there is NO measureable resistance between either of the slip rings & the steel metal. If your ohmmeter has very high ranges, you might see some readings of many millions of ohms, you can disregard that. I am concerned about LOW resistance values, which would typically indicate a short between the winding and the rotor steel. If you see low values, values of under 6 ohms, you have a BAD rotor. You can do this test while the alternator is assembled in the bike, but put pieces of paper between the brushes and the slip rings.
(2) Measure the rotor coil resistance. Short the ohmmeter (lowest resistance range if you have adjustable ranges) leads, & write down the value indicated. Now touch the leads solidly to the slip rings, one lead on one slip ring, the other lead to the other slip ring. Don't let the leads touch the frame. Subtract the first reading from the second reading. That results in the rotor resistance value. Early rotors were about 7 ohms, later rotors a bit over 3 ohms, and the last rotors just barely under 3 ohms. You may see some differences, depending on your meter ....and how solidly the meter leads connect to the meter jacks and the slip rings.
(3) If you have removed the brush holder, there is always a possibility you have not installed the insulating and any metal washers correctly. It is not commonly known that there are more than one version of the white plastic brush holders (involving how the wire from the brush went through the plastic area, and also how the snail spring fit to the plastic) and also more than one version of mounting the brush holder. Early models were mostly all the same, with cambric insulating washers on Df and D- terminal fittings. Then came models with grounding at the D- terminal, done with the washers, and lastly the metal "washers" became part of the housing structure. The D- is grounded right there at the screw-washer fitting (and the brown lead is the grounding wire to the voltage regulator) .....but the IMPORTANT thing is that you must assemble the Df terminal so it is NOT GROUNDED.
If the alternator is already assembled, remove the D- and Df brush holder push-on connectors. Install small pieces of paper between the brushes and the slip rings. Check that D- brush holder terminal is grounded to the alternator/engine case ....so indicated with a near zero ohmmeter reading. Check that the Df brush holder terminal is not grounded. If the brushes and rotor are in place, and you did not install the paper pieces, the Df resistance to the case will be quite low, but will be at least 3-1/2 ohms with any of the rotor types.
(4) The rest must be done with the rotor installed, alternator stator/housing in place, brushes installed and in contact with the rotor slip rings. You need not have the diode board connected nor any connections to the stator (both, your choice). There are RARE instances of a rotor being REVERSE magnetized during production or other testing, to such an extent that the magnetic field is not overcome by the weak current from the GEN lamp.
Temporarily reconnect the battery negative wire to chassis or engine ground. REMOVE the two push-on connectors at the brush holder DF terminal and the brown wire at D-. Jumper the D- terminal to any nearby convenient grounding place. While the D- terminal is supposedly already grounded, this insures that it definitely is. Connect a jumper wire, anything a few feet long and of gauge 18 or larger will be OK, from the battery POSITIVE (+) terminal, to the Df TERMINAL (not the wire you removed). You may see a small spark. A second or two is enough to polarize and add slight magnetism to the rotor. Remove jumper(s). Replace the D- and Df push-on wire connections and dis-connect the battery so it is safe to work on the alternator area, or even to install the outer metal cover.
DO NOT sandpaper the slip rings. You can clean the slip rings with a few drops of a quick evaporating solvent onto a clean rag. It is normal for the slip rings to be discolored black in the brush tracks.
Brushes wear out. They typically last, on average, about 70Kmi. That mileage is variable, depending on brush snail spring tension, how much dirt is in the air where you ride, & how much of the alternator output you use on average. When the brushes fail to contact the rotor slip rings properly, you will have problems with irregular GEN lamp indication, intermittent charging, & eventually no charging at all. Quite often the problem first shows up as a dim lamp or lowered charging voltage as rpm goes up, due to normal slight irregularities in the run-out of the slip rings, causing very slight brush bounce. When at least one brush fails to contact enough, the GEN lamp will usually not illuminate. Note that it is normal for the slip rings on the rotor to get black from the carbon brush.
HINT! In an emergency, put one or two small pieces of thick paper, such as cut from from a common matchbook, under each spring tip. This will allow a LOT of miles of good charging, until you can more conveniently replace the brushes.
When the brush length is such that troubles begin, they are actually more than long enough to work OK, BUT the snail spring can be mechanically prevented from pushing enough, or at all on the brush, when the brush wear is enough to allow the snail spring to hang-up, bottomed out actually, in THE SIDE SLOT in the brush holder (some brush holders, of the very early type, had no side slots, so the hangup was at the end of the holder, but same effects). When worn ABOUT half way or somewhat more, the brushes are usually not working correctly, or, soon won't be. You can see the condition of the brushes and snail spring contacting, by your #1 eyeball, with everything intact. Look CAREFULLY at BOTH snail springs, see if either is BOTTOMING on the white plastic holder. If NOT, there should be brush life left IF the spring is OK & applying pressure and the brush wire is not broken. You do NOT need a lot of spring pressure; excessive pressure is NOT a good idea either ....but neither is too little pressure!
There are two basic styles of brush holders, & they are interchangeable. They look nearly the same unless you look carefully. The difference is the SIDE slot for the snail spring. There have been two styles of brushes, also interchangeable. The very fine and soft stranded wire may come from the END of the brush, or the SIDE of the brush. Some brush holders have a groove for the brush style in which the wire comes out the side. Be sure to look carefully, assemble properly. Presently-sold brushes have the wires coming out the side of the brush, near the outer end, and holders have the slot.
Brush changes & tools required (read through thoroughly first, you may not need them all):
BMW standard on-bike tool kit.
(8 mm Spintite or modified nut driver or modified socket ...only if you decide to remove the brush holder, which is NOT necessary).
Good sized soldering iron, such as 250 watt soldering gun, or 100 watt large tip iron; . It is possible to use a soldering iron as small as 25 watts if the tip area is massive enough. If you join the old existing wire and the new brush wire, by soldering, you can use almost any low wattage soldering iron. Rosin core electronics type solder.
Long nose pliers or other device to help to avoid solder wicking; may not be needed.
Torque wrench and allen adapter is OPTIONAL.
Brush set, 12 31 1 244 480 (one set = 2 each). Some older numbers are 12 31 1 350 787; 12 31 1 243 004; 12 31 1 244 389. Your new brush set might not come with the insulating sleeves for the brush wires, so you should save your old ones, although sleeves are NOT a must-have.
Best to get brushes from your BMW dealership or independent BMW servicer. Napa has Echlin E453 (ECH E453). Probably made by Bosch as 1 127 014 009. Be sure your new brushes have the bevels mentioned in the next paragraph.
Stock BMW-sold brush dimensions: A brand new brush is .394" wide and .192 inches thick. From the flat outer end, to the center of the curved area, is .650". Thus, the 'nominal' specification is 5 x 10 x 16.5 mm. (formal brush catalogs will describe the brush as: 5 x 10 x 17 x 36.5 mm (the pigtail is 36.5 mm). Note that a brand-new brush has its 4 SIDE edges beveled, and there is another two bevels at the short width outer ends. These bevels are there to help the brush avoid 'catching' on the plastic holder. Note that as brushes wear, they not only shorten in length, but the sides wear SLIGHTLY. The PIGTAIL comes off one wide side, NOT from the very end of the brush.
Most autoparts stores sell brush sets for a variety of alternators used on many foreign cars, including BMW cars; these cars can be those manufactured from sixties to 90's, possibly even later. BMW, Mercedes, Porsche, VW; Volvo, Opel, Lamborghini ... lots more too. While these brushes might look the same, DO bring your calipers, and be sure they ARE the same, and have the bevels (or be prepared to file the brushes to get the bevels). When I say to be sure they are the same, I mean the general shape, bevels, leads coming out the side, but I also mean that the new brushes measure up to what I have in the above paragraph.
Brushes are available, often at the same price, but should always be the correct size and type, from your BMW motorcycle dealership and BMW independent. Some autoparts stores items are much more expensive than from BMW themselves.
* Brush holder (if you are not careful to avoid breaking it): 12 31 1 243 003
* Snail springs (two), IF yours are lacking enough force ( & note that not much is needed), 12 31 1 350 786. Many folks automatically replace these. I have not found replacement to be necessary most of the time.
On some brush holders the soldering point can be gotten to for both brushes without removing the stator, but the rear brush and snail spring is somewhat of a bear to get to without removing the stator. You will see what needs to be done by a look-see. On most brush holders, the soldering points are available conveniently ONLY by removing the stator (you need NOT unsolder the stator wires ...you simply must remove the entire stator assembly ...but use a piece of wood, not metal, to pry a wee bit all around the area the stator fits the engine case ...and do NOT crush/nick those windings! DO NOT scrape across the laminations either. Best way to avoid problems is to use a piece of hardwood, and avoid having it near the windings.
Both brushes are in a single, somewhat breakable (especially when old and brittle), white-colored plastic holder. The outer (forward) brush is relatively easy to get to, not so the inner brush. Due to irregularities in brushes, spring pressure, dirt, etc., the inner one MIGHT wear faster, so take the time to find out.
The snail springs are not to be tightened so much that they are nearly wound up solid. Typically, a new OR USED brush and spring, with spring properly fitted to the brush-holder metal tang, will take a bit under 1 turn of rotation to put proper pressure on the brush when the brush is on the rotor slip ring.
A little known problem can occur with the snail springs, mostly I see this now and then on the inside hidden spring (rearward one), but can happen on the forward spring. The snail spring can be installed with the steel mounting plate TAB on either side of the center part of the snail spring. If the tab is in the wrong place then the outer part of the snail spring MIGHT rub on the white plastic housing, this is because the spring will be a bit off center ....this can also cause the BRUSH to NOT slide smoothly in its holder. This will cause improper brush operation. Check that the snails are centered & that brushes move in and out smoothly when you have the stator off the bike and you can easily push the brush with your finger. Do NOT think you can test for this by pulling on the brush wires with the stator mounted, you can not.
Clean the brush holder after the old brush is removed, with Q-tips and a good fast drying solvent; you need no fancy solvents, even home alcohol is OK.
The brush flexible stranded wire is soldered to the brush holder metal plate. To completely install the new brushes just like the old ones, you will need a soldering iron with a substantial size soldering tip to hold enough heat during the soldering. Large heavy duty soldering guns also work OK. BUT, YOU DO NOT HAVE-TO solder to the brush holder metal plate! ...it is possible to join the wires, which means cutting the old brush wire to leave some length of it already soldered to the brush holder tab. You must be careful about not letting the solder flow too far, which stiffens the fine wires, and then they are more likely to break, over time and miles.
When replacing the brushes you have two choices. For BOTH, I recommend you remove the entire stator and stator housing AS ONE UNIT (do not unsolder any stator wires). I assume those things, below. You want to avoid damaging the plastic holder when doing a brushes job. I will explain that, a bit further down, in 4.
Method #1: Cut the old wires somewhat near the point where they solder to the TAB on the PLATE, leaving some of the old wire for soldering to the new brush's wire. You have to be careful when soldering these wires as solder wicking can occur, making a considerable length of the wire stiff, a bad idea as a stiff wire may not allow proper brush movement, & definitely makes for a potential for breaking from vibration. Long nose pliers or a pair of forceps, via heat absorption during soldering, will help prevent solder wicking.
Method #2: Since you have a large tip or powerful soldering iron, remove old wires, solder the new wires, the same caution about solder-wicking applies ...but you need only the long nose pliers or one pair of forceps.
Below is what Snowbum recommends. NOTE that you do NOT have to remove the rotor! You do NOT have to unsolder any stator wires!
1. Unplug all wires at the alternator, all are push on/pull off types. Take note of any that are not fitting tightly or are overheated, and fix these problems before reassembly, by cleaning with a fine-tipped tool of some sort and squeezing the female connector parts slightly. Failure to ensure clean and tight connections will result in them overheating, and likely lower electricity output.
2. NOTE the rotational position of the brush holder and other wires ...you will be removing and replacing the alternator stator/cover/wires as one assembly, back into the same position upon reassembly. If you try to use a wrong position of rotation, the three screws will line up OK, but the wires won't. Of the THREE stator connection wires right next to each other, their order is NOT important (some have individual separate wires, other years/models have one plug). Do NOT mix up the two rotor wires. D- is ALWAYS BROWN.
3. Remove the THREE long screws holding the alternator case to the timing chest. when reassembling, those screws should be equally but only moderately tightened, in back and forth patterns. NO need to be strongly tightened.
4. Remove the entire stator assembly as a unit. NO UNSOLDERING. Avoid any damage to the brush holder. NOTE that the brushes might get hung up on the slip rings area during stator assembly removal, so go at this stator removal SLOWLY, bit by bit, while keeping an eye on the brushes. If the brushes hang up, the brush AND/OR white holder can be broken by further prying. Pull up on a brush wire as needed, while slowly removing the stator assembly. To avoid breaking the brushes and brush holder during re-installation later, the brushes MUST, AGAIN, be lifted away from the rotor slip rings AS you install the case/stator. You do this one brush at a time, during refitting. DO NOT forget this!
Using a small piece of wood in one hand ....NOT a metal screwdriver!! (unless you are VERY careful not to pry on the windings nor nick the laminations) ....and SUPPORTING the outer alternator/stator case with the other hand ...to keep the stator and housing assembly from dropping on the floor when it releases ....CAREFULLY & LIGHTLY pry, evenly all around, at the open areas along the REAR side of the stator, where it meets the engine. AVOID TOUCHING or PRYING ON THE STATOR WIRES! DO NOT pressure nor scratch nor nick the steel laminations of the stator! Pry points are the timing chest metal to the alternator stator multi-layered metal stack, or, better said, the housing. Typically prying a SMALL amount, relatively evenly around, at the three opposing places along the circumference is all that is necessary. Remove the assembly straight out.
5. With the case/stator/brush assembly in your hand and away from the engine, all will be self-explanatory upon inspection at the inside of the stator assembly where the brushes attach.
6. For SOME brush holders, you need to remove the inside nuts to remove the holder for soldering, on other holders this is not necessary. The nuts holding the brush holder to the case are thin, and you may have to improvise a nut-driver. I use a SpinTite, with the end ground flat to avoid any tool internal taper. A SpinTite is simply a brand name of a tubular wrench. A thin socket, its end suitably ground flat to remove its internal taper, on your grinder or sander or lath, will also work fine.
7. When replacing the case/stator, be SURE the mating surfaces of the stator housing & the matching engine area are cleaned of all filth. Corrosion on the steel part of the stator can be cleaned with sandpaper or brass or steel bristle brush. Follow good procedures by never using steel wool around electrics. DO NOT nick or bend any metal of the stator, its housing, or the stator/engine mounting area. It is especially important not to pressure or otherwise damage the stator windings.
If you decide to clean the rotor slip rings, DO NOT use emery paper or sandpaper. Use a clean rag with a few drops of a quick evaporating solvent. Do not try to remove the black carbon beyond this solvent cleaning. I previously used to recommend a more vigorous slip ring cleaning, but it was misinterpreted, so the above information has removed the stronger cleaning ....and, frankly, it is not needed. If you insist on a more thorough cleaning, use a pencil eraser. MIND THE CAUTION ABOUT NOT BREAKING BRUSHES NOR THE WHITE BRUSH HOLDER IN STEP 4.
8. NOTE! It is altogether too easy ...to forget that one of the brushes is an electrically hot brush & the other one is grounded. If you have to remove the brush holder, do not fail to note where the washers are located, & how assembled. Failure to reinstall the insulating washers at the proper places, in the proper order, with any washer ridges in proper position, can result in no charging. There are markings on the stator housing. The D- marking is the grounded brush, and the BROWN wire connects there. Df is the ELECTRICALLY INSULATED brush. You will probably find the Df brush wire to be blue/black. Late model covers are less ambiguous, and the grounding post side is part of the casting.
9. Make a final inspection after assembly, and check that you have tightened the 3 long screws evently, and do not over-tighten. Attach all the wires by pushing them onto their respective male spades; and, as cautioned previously, be sure that the grouping of three at the stator are very tight fitting, the others decently tight fitting ....and note again that it makes no difference what order the three next to each other are attached, if you have separate wire connections there.
10. Be careful on points models (up to 1978), that the large aluminum outer cover fits properly to the rubber grommet located at the left side of the points cavity, as you face from the front. ALSO BE CAREFUL: Many a person has crushed the points wire, & had a no-start condition immediately, or much later.
Go for a 'round the World ride ...maybe 30Kmi? ...then inspect the brushes again. You might check the charging voltage every year or sooner. 14.2 is nice.
Revisions: © Copyright, 2017, R. Fleischer
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02/03/2003: Add brush dimensions.
03/30/2003: Add NOTE #1: and NOTE #2:. Add altbrushrotor.htm at top; minor other editing for clarity.
07/13/2005: Torque on center bolt of rotor added.
10/26/2006: Clarifications of no substantial importance.
05/10/2011: Update article for clarity.
09/18/2012: Add QR code; update google code and meta's; add note on not crushing the points wire and installing cover in the grommet carefully; edit a few places for clarity and emphasis.
10/09/2012: Expand section on rotor removal cautions, etc.
03/04/2013: Clarify a few small things. Increase information on the brushes specifications. Add a cautionary note on brush dimensions and type.
06/17/2013: Clean up article some.
11/02/2013: Add info on stator and rotor, clean up article somewhat for additional clarity; add hyperlink to Anton's article.
11/03/2013: Re-arrange items, add some notes, add magnetizing too.
06/09/2014: Clean up some, change emphasis a bit here and there.
08/03/2014: Modify slip ring cleaning
09/13/2014: Clean up article
01/01/2016: Update meta-codes, narrow article, increase text font, etc.
05/05/2016: Update meta codes, scripts, layout, fonts, colors etc. Clean up article. Correct ERRORS!...in how rotor is tested; improve procedures.
06/13/2017: Clean up colors, fonts, separator lines more.
12/02/2017: Major update. Reduce html, fix layout, minimize use of font and color changes, improve clarity.
Last check/edit: Monday, July 22, 2019
© Copyright, 2017, R. Fleischer
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