Alternator, Rotor, Stator, Brushes, etc.

Alternator rotor, stator, brushes, etc.
For BMW Airhead Motorcycles

…INCLUDES STEP BY STEP PROCEDURE,
BRUSH AND/OR BRUSH SPRING CHANGING.

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 text & photos will explain explain some things differently; and, I suggest you read his article. I have minor disagreements with it, BUT….it does have some useful information & has some photos you should look at. I have the most detailed and pertinent information here in my own article, below. Read Anton’s article here: http://largiader.com/articles/charging

The original /5 BMW Airhead motorcycles had a 180 watt alternator with the end that fits into the motor timing chest cavity being 105 mm in diameter. SOME 1974-1975 /6 bikes, & possibly a few barely into 1976, were made with the 105 mm cavity. These /6 bikes with 105 mm stators had 280 watt alternators, so it is possible to upgrade a /5 from the 105 mm 180 watt alternator to a 105 mm 280 watt alternator with the appropriate parts changes and the parts WILL FIT. The changes needed are to the stator & diode board at a minimum. If your /5 rotor measures ~7 ohms, which was the original value, then I recommend it be changed to a next version rotor of ~3.4 to 4 ohms; the electronics VR is optional, but recommended. ALL /6 and later stators had a center tap on the stator 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 considerably less than 280 watts. I suggest NOT using the very 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.

Technical information, mostly this is expanded information:

The original rotors of the /5 were 73.4 mm in diameter. Those were approximately 6.9 ohms and are usually referred to as the 7 ohm rotors. In 1974, a center tap was added to the stator windings, & the rotors now had heavier wire and were 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. The rotors are generally NOT marked with a part number.

In 1975 or 1976, the ROTOR size was made slightly smaller, at 73.0…probably some bikes had enough crankshaft whipping to allow their 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, confusing. The STATOR HOUSING has the alternator number on it, and the Bosch number, which for these 1975 or 1976 changes meant to this number: 0 120 340 005. These have slightly lower low rpm output. No books nor commonly available literature describes these things completely, except in this article you are reading.

Most of these things are a bit moot. The more important things (?) are 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 fewer total watts deliverable at any rpm. Another wee bit of information is that the Authorities (Police) version also had very slightly different dimensions of rotor and stator.

The final change to the alternators came in the early 1990’s. The rotor became 2.8 ohms, the stator also had a change in resistance, and was now 0.8 ohm sections, & the stator assembly was 12-31-1-244-641. The maximum output was a bit lower, but output started at a lower rpm. I do not recommend using the last produced parts in an earlier model.

The result of the various combinations that the factory used is that alternators from the time of introduction of the /5 in December of 1969, to the end of Airhead production in 1995-6, was output wattages could be 180, 234, 238, 240, 250, 260, 280….my values here include the Authorities (Police) versions.

I have data on my website obtained from REAL testing, on a known perfect system, a 1983 bike that I personally owned & prepared. The article is: 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 present article.

Voltage Regulators:

The earliest voltage regulators were mechanical-electrical; designed for the early 7 ohm rotors used on the /5 models, but mechanical regulators were used even with the very next lower ohm rotors of the /6….until BMW finally went to electronic regulators. The change to electronic regulators happened initially in the nearly-same-looking, but shorter, metal cans. Most were made by Bosche. Eventually the shorter metal can VR was dropped in favor of the flat plastic VR box. The metal can regulators, mechanical-electrical or electronic, are all adjustable for voltage output …and I recommend adjusting them, per articles on my website …your battery will appreciate it….so will your wallet, as the batteries will last longer….and the batteries will be more fully-charged. BMW tended to set the original regulators to a slightly low output. Typically that meant 13.8 volts, at average riding temperatures.

Almost any combination of any of the alternator parts can be usable. The main restriction is the 105 and107 mm stator sizes, although if anal enough, you could exchange the timing chest cover OR bore the 105 hole for the 107 mm stator which I recommend you do NOT do. Anton’s site has photos of the two.

THE LAST OF THE Airhead alternators WAS RATED AT 240 WATTS. It uses a further-changed stator & further-changed rotor winding resistance. 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. BUT, you will NOT damage anything by trying combinations of whatever parts you happen to have!,,,,except that you must pay attention to the 105/107 mm information.

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, you can disconnect it at the speedometer cable hollow bolt …. or frame place someone put it at, …& not at the battery, if you prefer to. BE SURE the wire lug end can NOT contact anything (tape it, or put electrical spaghetti over it). The battery MUST be electrically disconnected one way or the other; removing all the negative wire(s) attached at the negative battery terminal is usually the best method if more than one wire is at the battery negative terminal.

Only with the battery disconnected is it safe to remove the outer timing chest aluminum cover of the timing chest on motorcycles with the Bosch type of stock alternator and 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. Clean the hole or peg as/if needed.

If you have a pre-1979 model, be cautious regarding the rubber strip located around the ignition points cavity, a rubber grommet is also in that area, & the tachometer drive,… particular attention is needed 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 & washers, then wiggle 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 and when replacing, do not overtighten those screws.

The earliest aluminum outer covers did not direct as much cooling air to the alternator and can be replaced. The same goes, especially, for the NON-louvered outermost fairing models covers. That outer painted fairing cover originally was solid, but later versions had louvers 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 information!

To remove the rotor, you must remove the stator housing first. Simply pull-off the push-on connectors, unscrew the three long screws, and pry the stator away from the motor. BEST TO NOT USE A SCREWDRIVER! DO NOT PRY AGAINST THE WINDINGS! PRY A LITTLE BIT AT A TIME, ALL AROUND AT THE MOTOR CAVITIES. I USE A PIECE OF PLASTIC OR A WOOD TOOL….OR, A SCREWDRIVER, BUT VERY CAREFULLY!

If you are removing & replacing a ROTOR, THEN ONLY A HARDENED BOLT TOOL should be used, DO NOT use a conventional fingered puller. You can MAKE a tool to do this job, but the tool must incorporate HARDENED parts that will be fitted inside the rotor during use. I HIGHLY recommend you purchase the proper ONE PIECE 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 these cautionary notes on rotor removal. If the tool you use is not hardened, it WILL BEND inside the rotor. THEN YOU HAVE A REALLY BIG BAD BIG PROBLEM. I suggest you use ONLY the ONE-piece type of tool, because there have been really bad problems with cocking angularly if using a two-piece tool!

How the rotor attaches to the crankshaft:
A bolt tightens the rotor to the crankshaft. It screws through the limited depth of threads of the rotor; that is, the rotor has an area of no threads. The end of this bolt screws into threads in 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.

How the rotor is removed:
The rotor is removed, when needed, by a simple method. The original rotor bolt is first totally removed. The hardened special rotor removal tool is then screwed into the rotor, and it passes through the rotor as does the normal bolt…..but the removal tool 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 tight enough, the rotor will very suddenly POP OFF the crankshaft (so be ready with your other hand already holding the rotor…to catch it …so it does NOT fall to the floor).

The critical part is the removal tool portion that is inside the rotor and crankshaft nose. THE 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 TAPERS, male & female 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 the degreaser. I use acetone. Be sure the rotor end that goes into the rubber seal is not nicked, and clean that rotor area too, although it can be faintly oily to help protect the seal. Simply push the rotor onto the tapered crank nose and the seal. Reinstall using the regular bolt. Do NOT over-tighten the regular rotor bolt. BMW’s tightening specification is too high, in my opinion. 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 enough. A locking washer is under the bolt head.

SO, despite all my cautions, perhaps you did not see my information…..you used a non-hardened bolt or other tool, perhaps a two piece tool… and you have bent the tool(s) inside the rotor……WHAT NOW?

Typically, the symptom is that your ‘tool’, no matter how tight, will not pop the rotor off ….and may have 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 & 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 breaking the tool, perhaps….well….You are now at the GOTCHA point.

The tool has either bent, and/or canted sideways if a 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 two 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+ out, you are likely NOT in trouble…just get the correct one-piece bolt tool.

Assuming the worst:
You have two choices in MY opinion, depending on what items you originally put into the rotor.

I would try THIS 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/concerned about saving the rotor.

If the above method does not work: make up a very stiff/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 that crankshaft nose!

Hints:
On very rare occasions with a brand-new rotor, or a rebuilt one, or a rotor that was tested with possibly reversed polarity power source, …you may find that the system will not charge at all; or, charge output is low, and you know the diode board is OK, etc…. you might have installed the wrong rotor resistance. Usually, but not always, 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 the problem, I now recommend that any time you install a rotor, that the following tests be done. Frankly, I would do the tests on new or old, and rebuilt rotors too.

(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 quite LOW resistance values, which would typically indicate a short between the winding and the rotor steel. If you see low values, probably values of under 4 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 3 to 4 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 fit the meter jacks and the slip rings.

(3) If you have removed the brush holder, there is always a possibility you have installed the insulating and any metal washers INcorrectly. It is UNcommonly known that there are SEVERAL versions of the white plastic brush holders (involving how the wire from the brush went through the plastic area, and, how the snail spring fit to the plastic) and SEVERAL versions of mounting them. 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 itself. The D- is grounded right there at the screw-washer fitting (and the brown lead is the grounding wire to the voltage regulator D- and brush D-)…..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, since it includes the carbon brush.

(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).

Temporarily RE-connect the battery negative wire to chassis or engine ground. REMOVE the 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 from it). 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 is safe to work on the alternator area, or even to install the outer metal cover.

Theoretically, such magnetization is not needed, but there ARE rare instances of a rotor being REVERSE magnetized during production or other testing. Some rotors, so magnetized (and the magnetic field is very weak), will not respond properly to the WEAK current from the GEN lamp, hence this caution to magnetize it correctly.

DO NOT sand 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 from the rubbing by the black carbon brush.

Brushes:
Brushes wear out, they USUALLY last, on average, about 70000. The mileage is varies, depending on brush snail spring tension, how much dirt is in the air where you ride, & how much of the alternator output you use. 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. 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 at all, the GEN lamp will usually not illuminate, or be intermittent, and can even be variable day to day.

HINT! In an emergency, you can put one or two very small pieces of paper, such as cut from from a common matchbook, under the spring tip. This will allow a LOT of miles of good charging.

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. This happens 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 identical unless you look carefully. The difference is the SIDE slot for the snail spring. Also there are two styles of brushes, also interchangeable, the differences being 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 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; rosin core solder. 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.

Long nose pliers or other device to help to avoid solder wicking; may not be needed.

Torque wrench and allen adapter is OPTIONAL

Parts required:

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, so you should save your old ones, although sleeves are NOT a must-have.

Best to get brushes from the BMW dealership or independent BMW servicer. If you have a problem with that, you can go to Napa and get the Echlin E453 (ECH E453). Probably made by Bosch as 1 127 014 009.

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 MAY come off one wide side, and NOT from the very end of the brush.

Warning: Most autoparts stores sell brush sets for a variety of alternators used on many foreign cars, and even 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 reasonably closely to what I have in the above paragraph.

Keep in mind that that the brushes are available, often at the same price, but are the correct size and type, from your BMW motorcycle dealership. SOME autoparts stores are much more expensive than 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 that 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!

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, 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 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.

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. NOTE!! You want to avoid damaging the plastic holder when doing a brush 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 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.

Here 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. They 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 UNimportant (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. NOTE that when reassembling, those screws should be equally tightened and only moderately tightened, in back and forth patterns. NO need to be more than lightly 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)….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/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 internal taper. A SpinTite is simply a brand name of a specific style of tubular wrench. A thin socket, its end suitably ground flat to avoid the internal taper, done on your grinder or sander, will also work fine (I modify them on my lathe).

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 a common file or even sandpaper 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 slip rings, DO NOT use emery paper or sandpaper. Use a clean rag with a few drops of a quick evaporating solvent. I recommend you do not try to remove the 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. MIND THE CAUTION ABOUT NOT BREAKING BRUSHES NOR THE WHITE BRUSH HOLDER IN STEP 4.

8. NOTE! It is altogether too easy, many have been fooled… 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 connection plug wire to be blue/black.

9. Make a final inspection after assembly, and check that you have tightened the 3 long screws EVENLY, 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 these three next to each other are attached.

10. Be very careful on points models (up to 1978), that the outer cover fits properly to the rubber grommet located at the left side of the points cavity, as you face from the front. 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.
🙂

Revisions:

05/05/2016: Correct ERRORS!…in how rotor is tested; improve procedures.
05/13/2017: Copied to Airheads.org website. Edited and finished 05/14/2017.
06/20/1018: Clean up code some.
01/31/2021: Clarifications and emphasis.

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