This is by no means a complete list of technical hints for your BMW Airhead motorcycle.   The Author’s website has well over a hundred technical articles.  The Author’s website is:
HTTPS://BMWMOTORCYCLETECH.INFO/INDEX.HTML

1. If you are trying to find out if your voltage regulator is faulty, or, bypass it in case of failure while on the road, and thus obtain charging; here is a simple method. I carry one of these ‘tools’ with me in my on-bike tool kit for testing purposes or on-the-road emergencies.

Obtain two each standard male spade connectors. Any autoparts store will have them.  These may be called ‘disconnects’ or ‘push-ons’. Crimp or solder them to a piece of stranded insulated wire about 6 inches long. To use; simply disconnect the plug from the voltage regulator under the fuel tank. Insert the male spade ends of your test lead into the plug’s female openings for D+ and DF; those are the OPPOSED female openings. Do NOT connect to the female that has a brown wire. You’ve now removed the regulator from the system and ‘told’ the alternator to go to as high an output as it can…which it will as you increase the engine RPM, which may take as much as 4000 rpm or so. WARNING, this test is for brief testing only or for limping home at low RPM.  This is because riding any distance at high RPM will cook your battery and is also hard on the diode board, and every other electrical item. If your charging output is still low with the jumper connected, you have other problems.  If you have a voltmeter with you, don’t allow the battery terminal voltage to go over 14.9 volts.

2. Do NOT remove the timing chest outer cover without removing all the battery terminal negative lead(s) first. Failure to do so can cause sparks and a diode board or other failure.  IF your battery has only the one (1) wire on the battery negative terminal, that wire will be very large in thickness and will be seen going to the hollow speedometer cable-holding bolt at the right rear of the transmission, …. then disconnecting that wire at that hollow bolt is OK, there being no need to unfasten at the battery…unless you want to.  Be sure the wire cannot touch the chassis or engine, etc., while you work on the timing chest cover and area. If you have other wires connecting at the battery negative (-) terminal, then remove all the wires at that negative terminal, and insulate them from touching anything like the frame or the negative terminal; and then there is no need to disconnect the large wire from the hollow bolt.

3. Do not install a battery disconnect switch; I find them mostly poor in quality and function. If you insist, use the marine type.

4. Do not over-tighten the hollow speedometer screw/bolt at the right rear of the transmission, where the large battery cable connects to. That hollow screw holds the speedometer cable in place, and the battery negative wire in place, and also provides for transmission and driveshaft venting. To make this an easy disconnect, slot that wire lug just enough to fit over the screw threads….but DO BE SURE to use the two stock washers. The speedometer cable boot has been the source for many $$$ transmission woes.  YOURS must be in good condition. Be sure the top of the boot seals to the speedometer cable jacket, you can use RTV.  WATER running down the cable, past the boot, and into the transmission, can quickly do $$$ damage to the transmission. If ANY question about the boot, replace it.   I recommend you do NOT use a zip-tie or similar at the neck of the boot, as it may distort the boot enough to allow water to enter the transmission.

5. Do NOT use an ohmmeter to test the Hall device in the ignition canister (used on 1981+ models). Most ohmmeters will pass too much current through the Hall device (a special type of transistor), and may ruin the delicate Hall device. It is probably best not to use an ohmmeter on the ignition black box (“module”) under the gas tank. That module has 7 pins, numbered FROM THE RIGHT SIDE. Pin 1 is for the coil; pin 2 is ground (to circuit point 31); pin 3 is ignition trigger minus (-); pin 4 is ignition/light switch (to circuit point 15); pin 5 is ignition trigger positive (+); pin 6 is the “0” ignition trigger; pin 7 not used.

To test a canister for failure of the Hall element; disconnect the three pin plug in the timing chest outer area. You must remove the very thin round bale wire first. Turn on the ignition, set the bars kill switch to center (RUN position), and using a bent paper clip or other means, repeatedly ground the center pin of the mating plug that is part of the engine harness (not the canister plug). Each time that should produce a spark at the spark plugs.    If you do not wish to test the canister in this way, another method is to not mess with the plug assembly, and just move the KILL switch back and forth, each movement will or should produce a spark at the spark plugs.

To safely (for the system) see that spark at the spark plug gap, have the plugs removed, the plug caps must be pushed back onto the spark plugs, and plug bodies MUST be grounded, so use a cylinder or head fin and something to be sure the spark plug metal body (the HEX is good for this) is in secure contact to the fin metal. Failure to ground a sparkplugs will almost certainly cause expensive damage; and that damage may not show up for a long time.
An extensive article on the electronic ignition is here:  https://bmwmotorcycletech.info/ignition.htm

6.  The large diodes in the diode board are Motorola 1N3659 (cathode to case) and 1N3659R (anode to case). They are rated at 50 volts, and 30 amperes at 100 degrees Centigrade. If replacing, I suggest you use higher rated diodes such as the 1N3660 (100 volts) or 1N3661 (200 volts). Be very careful pressing them in and out. Lead length varies on diodes depending on what the manufacturer decides to do, no matter what the books say! If the lead from the diode is long enough, and on a brand new diode it is usually is plenty long, FOLD IT over onto the printed circuit board, FIRST scraping away the coating over the copper on the board, before soldering. Use a 50-50 solder rather than 60-40; plumbers wire solder is usually 50-50, and usually does not contain flux, which will be needed. Be sure to use rosin flux.  If the existing large diodes on the diode board are showing signs of heat distress at the solder joint of that diode wire to the PC board, and IF the wire is NOT folded over for a large solder joint; the board could fail, and the best fix is tricky to do, which is to clean the board of coating using a gel paint remover, and then drill a tiny hole through the copper printing material, and add a piece of solid copper wire, soldering it as a folded-over tab to the PC, and at a tightly wrapped connection on the diode lead. Use of 50-50 solder, and not doing the tricky drilling, etc., may also work. You need not recoat.  Few of  you will ever do more than clean the area around an overheated diode connection and resolder it with 50-50.  Replacing diodes is much more of a hassle, and only the nerdy should attempt it.

7. Measurements can be taken on your Airhead to determine connections and switches condition, with various components turned on and off, particularly the heavy drain of the headlight.  With the ‘secret’ method shown here, no subtracting of two readings is needed.  Simply attach your voltmeters positive (+) lead to the battery + post itself, and using the voltmeter negative lead as a test prod, proceeding to various testing points down the system. ANY voltage drop over 1/4th of a volt at a point that is supposed to be at battery voltage, is a cause for investigation. BE SURE your system’s ground wires (brown) are firmly secured, as well as battery leads, and so on, before spending time doing any of these tests.  Many a problem will come about from a loose screw holding a solid brown color wire to the frame (typically near the horn or backbone of the frame).

8. Your headlight shell may contain an unused parking lamp socket. Some may want to put a truly usable lamp there; one that is not as powerful as the headlight, but will do considerable illumination during the daytime, to warn oncoming vehicles; yet reduce over-all electrical consumption, as the headlight can be turned off (various means for that). The lamp suggested is a Philips 12452; a 10 watt quartz lamp. There are others, listed on the author’s website, in the lamps article. Some have done an additional modification. The ignition switch can be rewired, moving one wire, to allow ignition-on, and bike to run, in the PARK position. Otherwise, one needs Euro controls on the bars. This PARK position modification applies to many models. Do NOT put quartz lamps into the eyebrow of the RT….too much heat for the plastic.

9. DO NOT over-torque, it will be expensive if you do, the M6 nut that holds the centrifugal ignition advance to the camshaft tip on the pre-1979 models. Proper torque is NOT OVER 4 ftlbs, IMO; rather than the factory setting OF 4 ftlbs.   Use an INCHpound wrench if you have one.  DO NOT use a large value foot-pound wrench. I always do this nut by FEEL, but you may well want to use a torque wrench, and try about 3 footpounds, that means 36 inchpounds.  If the tip of the camshaft breaks off, you can make repairs that last and work well, see the author’s website for the instructions.  AVOID this by NOT overtorquing.

10A.  Around the end of 1972, BMW changed the design and specifications of the automatic advance unit (ATU), for the /5 models. Previously the maximum ignition advance was at approximately 2000 rpm. The modification moved the point of maximum advance to about 3000 rpm.

10B. During early Airhead production the position of the POINTS CAM ITSELF to the camshaft (via a change in the position of the camshaft GEAR to the camshaft), and the markings on the flywheel, were all changed. The results of these changes were that the STATIC (S mark) timing of 9 degrees BTDC was UNchanged (of course the OT mark was still top dead center for the piston), but the maximum advance was changed. Because of the changes to the points cam, and that the long dwell points cam was overheating on Police bikes which had radio interference metal cans over the coils, the dwell angle was also shortened.

10C.  With today’s lower octane gasoline’s, the original /5 2000 rpm advance maximum is no longer acceptable. One easy change is to put on the later stiffer springs. This information is also on the author’s website.  You can also shave the weights.

11A. When you purchase tires, be aware that the early Airhead snowflake wheel rim design is for use with tubes. Many HAVE modified the valve stem hole (or, used a BMW metal valve or similar that FITS the stock hole!) and are using tubeless tires withOUT tubes. I am not convinced that tubeless tires on WM2 rims are truly safe enough. I HATE fixing rear flat tires on my tube tires, BUT, the thought of a high speed sudden air loss crash keeps me from doing something stupid. YOU do what you want! Do I consider this highly unsafe? No, I do not. What conditions might it be less safe in?….my GUESS is that it would be if you ran into a very large and deep chuckhole in the tarmac, which seriously dented the rim.  MOST tires that are marked Tubeless, are OK for use with tubes. Most manufacturer’s allow this, with a recommended one speed rating reduction.  To allow slower release of air on tubed tires if one gets a puncture, it has been proposed rather often that one could add an O-ring at the valve stem, then run the knurled or hex nut down to the rim. I am not convinced of the wisdom of this approach. The stem nut, as all of you should know, is not necessary, and is only needed AS HELP when fitting a tube into the tire and wheel. If you leave that nut on the wheel, I highly suggest you run it up to the valve cover cap…NOT down to the rim. With the nut at the valve CAP, the tube can shift a small amount in the tire if the tire decides to move on the rim (happens), without ripping the valve assembly out; which causes you to lose all your air VERY suddenly. A SLOWER loss of air is preferable when riding for advance notice of a pending flat.

11B. SOME 120-90/18 size tires will fit late 70’s to 1984 airheads. The original size was, of course, 4.00-18 on all but a few models. Models from 1981 to 1984 may or may not require the right side tophat wheel spacer be changed (original was 9.2mm thick, the thicker one is 10.7mm and is part number 36-31-2-301-737). Models before 1981 probably will require you to change this spacer to that number. This centralizes the tire in the swing arm better, to avoid rubbing, said rubbing might only show up at high speeds. The 120/90/18 size tire works best on the wider 2.75 inch rim used on the RS and RT models. The 120 tire is much harder to remove from the bike, even when fully deflated, and moreso on the drum brake models….the 110 size is a better choice for many, if not most, and will give a better handling feel too.   It is much easier to remove, and may NOT require the change of spacer, although I recommend it.  The INCH size, 4.00, is still the best choice.

11C. The CLASSIC ride of a BMW is had only with the original type of tire, a soft wall tire like the Continental K112/RB2, in the original sizes.

11D.  On the front, the stock 3.25-19 tire can be substituted with a 3.50 or a 90/90 or 100/90. Different tires MAY require different tire pressures, and will handle differently. The large size tires generally give a more stable feeling, but are not quite as quick handling. You may not notice the difference. Early front fender supports (a sort of fork brace) won’t allow a wider 100/90 front tire…and can be changed for the later brace ffrom the 1977-1980 /7 series.  That brace is 46611234907, and you may need the later fender.    Modern tires tend to have stiff sidewalls, are belted usually, some include radial plies.   Modern tires will almost for sure require rather considerably more tire pressure than is in your owners book.  Front pressures of 32-36; rear of 38-42, are typically required for today’s tires.

RESAID:   Tire pressures shown in your owners manuals, for ANY year Airhead, MAY BE too low for MODERN tires. This leads to mushy handling, shorter life, and less crisp handling. You may have heard that you can determine the proper pressure for the tire, weight, speed, etc., of your type of riding, by measuring carefully the pressure before and instantly after a ride at moderate to higher speeds. While true in general, the change is small, on the order of about a pound or two or sometimes slightly more….and hard to read accurately. SOME tires don’t follow this rule of thumb. It use to be called the 8% rule (some used 10%). NOTE that many tire manufacturers are erroneously  using BMW’s originally stated pressures, and NOT their much earlier and more accurate recommendation (not all had accurate recommendations). I think this due to lawyers.  I think you will find ONLY the TRUE original type tires to really need use of the old original book values for pressures, but even then, I suggest using the two-up high speed values.   Mark my words about tire pressures!    BTW, by the late eighties, BMW owners manuals were showing higher pressures.

Road tires are designed to be operated at a temperature of around 250 degrees Fahrenheit at the contact point & quite a bit cooler up the sidewall. Tires have many ratings, and motorcycle tires are now becoming more compliant with the type of ratings that the car tire manufacturer’s have had to put on the sidewalls for some years. There is a letter code for load, a letter code for speed rating….and some are coding for wear. Car tires are coded for temperature and wear/traction, and motorcycles are beginning to have this sort of thing. The 8 or 10% rule was that after a decent ride length (20 miles at cruising speed?), one quickly measured the tire pressure quite accurately, comparing that reading with the reading before you began riding. The tire pressure should be increased 8 to 10%. If too low an increase, decrease pressure and retry from cold; if too high an increase, increase pressure and retry from cold. The increase from riding was supposed to be due to flexing effects, and some other things. Use this rule, which I recommend AGAINST, only with caution and a bit of skepticism.

You may be surprised to learn that the difference between tires of various speed ratings is SOMETIMES just a matter of tread depth, sometimes the rubber is different though. Often there are other differences, of course. As a GENERAL rule, if you plan on purchasing a tire, getting a tire rated for your particular driving speeds, considering original specification, is more likely to get you a longer-wearing tire. Tire heat kills tires. Deep tread…all other factors kept the same…means more heat from tread squirming. High speed and high loads means LOTS more heat. S rated tires are OK for occasional spurts to 112mph; H for 130; V for over 130; and the crotch rockets use Z tires for over 149mph. Adding a tube to a tubeless rated tire will reduce the speed rating one position. It is NOT UNUSUAL to purchase an S or H rated tire instead of a V rated tire, and get more miles before it wears out, and have better handling at moderate to moderately high speeds as well.

12. BMW has used several types of wheel seals, felts, retainers, etc. over the years. Some of these are interchangeable, some are just updated versions. Variances exist between the disc brake and drum brake wheels and spoke wheels, and even between left and right side parts, sometimes on the same vehicle! There were some real odd-ball situations, such as the rear drum brake wheel of 1978.  This situation ended in the early 1980’s.  I have the information in my website.

13. Up through 1976 spark plug caps were 1000 or 1200 ohms, not the later 5000. It really does not make a much difference if you use 5000 on an early airhead. For the PRE-1981 machines, that do NOT have electronic ignition, the use of 1000 or 1200 ohm caps gives a slight advantage sometimes, with NO downside unless you have a sensitive AM band radio. NEVER use resistor wires and never use resistor spark plugs. You must NOT use anything but 5000 ohm caps on 1981+ models which have BMW electronic Ignition.    See the Author’s website on the various spark plugs, spark plug caps, etc….and the ‘new’ problem with Bosch plugs.
https://bmwmotorcycletech.info/sparkplugs.htm

14. Normal shifting, let alone hard use, can be hard on the U-joint bolts at the rear of your transmission. If those bolts loosen up at all, they will then continue to do so, and eventually they will come out and cause a LOT of damage. When the U-joint becomes disconnected or left hanging by only two (or, one) of the bolts, it will likely rip the entire rear end off your transmission, causing you to have a real bad day. I have personally seen this happen on a R60 and a R75/5; and, repaired many others. The bolts on the early models were to be torqued at 17-19ftlbs, for the 1977-1980 models the old specifications were 28-31ftlbs. From 1981 on, the factory says 29ftlbs. I use 29 footpounds for all models all years. In 1983 BMW stopped using the lockwashers under the bolts, the reason was that when a lockwasher partially broke and got thrown from the bolt by centrifugal force, the bolt was now able to eventually get quite loose quickly, and the other 3 would soon loosen up. BMW started using a new heat treated M8x13 bolt, and the part number is 26-11-1-242-297; this part is 1.5mm shorter than the original ones that used the lockwashers. I HIGHLY recommend any lockwashers be tossed and the shorter bolt used!! The longer original bolt must NOT be used without lockwashers; and you should throw away these old longer bolts away. These various bolts supposedly stretch when they are fully torqued to specifications. They are supposedly not to be reused, but I am well aware that lots of folks, including some shops, and ME, reuse them without any, EVER, problems. The only easy way to tell if a bolt might have stretched is to screw one in by hand (just your fingers). If they screw in by just fingers, they are likely not stretched and likely can be reused.  After testing, remove the bolts and then install them AFTER cleaning the male and female threads (must NOT be oily) and DO use Locktite in the medium strength, which is BLUE.  You need not repeat the test if you torque to 29ftlbs.    I repeat again: do NOT use the original 14.5mm length bolts and lockwashers! … IGNORE any parts person at your BMW dealership that tells you BMW has gone back to the longer bolts and lockwashers…that is NOT True!! Torqueing these bolts has proven to be a bit of a pain for some. Your torque wrench and socket just won’t ‘get in there’. BMW makes a tool for this purpose, the part number ends in -560. This tool….a piece of Germanic Craftsmanship (NOT! Pretty!), is really just a 3/8 drive piece of round material, with a slot, and a hacksawed off part of a 12 point 10 mm size box-end wrench, pressed and welded into that slot!!! It is perfectly OK to use the 10mm ring spanner (flat box wrench) that BMW put in the stock tool kit, and give each bolt a ‘good grunt’. Loctite BLUE first!  Aftermarket adaptors are available from BMW motorcycle tools and parts suppliers, that enable your 3/8″ square drive torque wrench to be used at the driveshaft U-joint special 12 point bolts. Use the appropriate correction setting on the torque wrench.

If you use such an adapter on your torque wrench, you are making the torque wrench LONGER by the length of the center-to-center distance of the tool. You will have to calculate the effect, for your own torque wrench.  A photo of the original BMW tool and the aftermarket one, is on the author’s website.  You can also adapt the stock tool kit dual spanner mentioned, etc.

15. In 1985 BMW modified the rocker arm assemblies.  Airheads now came with a new type of rocker arm assembly with adjustable end play, by shims. The purpose was to quiet the valve noises. IMHO this modification did only a little noise quietening and costs a whole bunch to convert to. I also think the narrowing of the rocker itself was a poor idea.   Between the beginning of the /5, until 1985, there were a number of changes in the valve gear, most of which can be installed, one at a time in many instances.

In 1985 BMW decided that the addition of some relatively hard silicon rubber pads/inserts into strategic places on the fins, at top and bottom of the cylinders, would quiet things, by stopping ‘metal ringing’ of the fins…sort of like hitting a bell; that type of ringing. These DO help, maybe even help cooling due to turbulence added. The inserts are under #11-12-1-337-818.  24 are required.

For those of you that feel that cost is never to be considered for your BMW, the entire kit for the rocker conversion for your older BMW is #11-33-9-057-699. Please be advised you will may need new support bushings, part is #11-12-1-261-405. There are some complications in using the kit, so ask on the Airheads LIST….and/or, see the Author’s website articles.  Depending on what year and what is actually in your airhead, you may elect to do nothing, or to add some or all of the various changes. One of the simple changes is to install the later pushrods.  The earliest rockers did not have needle bearings, but had sleeve bearings.  They wear in an egg-shaped manner.  The author’s website has information on how to switch them around and gain a LOT more miles on them.  Note that some faultily made needle bearing versions of rockers were produced, information on the author’s website.

Some of you may have occasion to remove your rocker shafts, perhaps for a valve job, gasket or O-ring at the cylinder base, whatever. BE ADVISED that if you assemble some year models of these shafts incorrectly, you will lose oiling to your upper end! Rather than a long paragraph here on identifying which is which, simply follow these instructions: The correct assembly is for the off-center punch-prick marks on the shafts, which are on one end only, to be ON TOP, FACING OUTWARDS. Various shafts have been made. If there is a small round discolored center area on one end of the shaft, it goes on top.

16. Brake squealing: All sorts of fixes are touted, including glues and pastes, and BMW car type anti-squeal backing plates (those are NOT AT ALL safe if pads are near new thickness);… and some will work for some time, as will changing to a soft pad lining material. While different models of our airheads are specified with different brake material, they are ALL designed to be used rather vigorously….specifically the design is for the worst case conditions! To help avoid squealing you need to use your brakes at speed or down a steep mountain pass, or pulling a trailer, carrying the wife…etc. Gingerly using the front brakes, which many seem afraid to actually use vigorously, is a PRIME reason for squealing. If you seldom use your brakes hard, and mostly just use them kind of gently, the SURFACE of the pads will “HARDEN” (actually, chemically change). This will cause squealing. MOST of the time, NOT ALWAYS HOWEVER, if I hear a BMW near me that is squealing, I usually guess that the rider does not use his front brakes much. Rear discs sometimes squeal too. Much more on the author’s website, in the brakes article, including information on squealing from faintly not-releasing brakes, etc. But….if you remove the pads, a very easy job, you can place them on an upturned piece of fine grit sandpaper on a flat piece of glass…whatever…..and make even-pressured figure eight motions, and remove a SLIGHT amount of material. Adding a SMALL DAB of anti-seize compound to the CENTER of the pad metal backing when reinstalling, may help also; I usually advise against this.

17. Some models of BMW’s, those with ‘swinging ATE calipers’, have an adjustable cam at the bottom of the wheel brake caliper assembly; inside a capped area. You can use an ink marking pen on the disc, and adjust the cam to give equal erasure as that brake is applied.  The adjustor needs to be lubricated.

18. When cleaning and lubricating the starter motor engagement parts (often called a Bendix Drive), use a medium to light grade of SILICONE grease but you CAN use common thin high temperature grease.  If you remove that starter, it must be carefully re-installed, if canted in the slightest the nose will break eventually.   Be very cautious about fitting other than the stock original starter motor.  Photos of the problems, easily fixed, are in my website.

19. Front fork filling varies by model number. In 1983, BMW had a service bulletin about fork levels. Fork oil should be replaced approximately every 10K or so. BE SURE to drain WELL, moving the forks up and down a bit to be sure. Let them drain overnight!  Amounts shown here are the latest corrected amounts for wet refill..that is, the fork has NOT been disassembled and cleaned and dried.

Per leg:

MOST models to 1980: 235 cc
R45, R65,R65LS, R80ST: 190 cc

Not noted models to 1984: 220 cc
R80R and R100R: 410 cc

R80GS and R100GS: RIGHT leg SAE10 and 440 cc, LEFT leg SAE 15 and 410 cc
From 1985, the R80, and R65 from 1986: 300 cc
From 1985, R80RT; R100RS, and from 1987 the R100RT: 320 cc

You will find that a 5 weight or 7-1/2 wt oil is about correct, with a 10 wt too stiff, except as noted.

CC means cubic centimeters, and is interchangeable for our purposes with ml (milliliter). I highly recommend the use of a graduated flask…or…at least a known accurate container…when installing the correct amount of oil. Plastic graduated flasks are available cheaply. You can also use an old graduated BMW fork oil container. You can, on some models, such as a R100RS or RT of 1983/4, measure the oil level quite accurately with a piece of welding rod, about 1/8th inch max diameter, inserted to the very bottom of the fork (do this through the removed bolt at the top) you may have to jiggle the rod some to get it over the internal ridge and down to the bottom). The proper depth of oil is 11.8 inches. Other models use different depths, and some have no specification. The R65 for 1980 and prior is 3/4 to 2″; and other early models are 1=1/4^th to 2-1/4^th inches. These are with fully extended forks (wheel off ground). You many find books saying that up to 1977 the large bore bikes are 437 mm (17-1/4^th inches) from top surface of fork top plug to top of the oil itself. Then, to 1980, 50 mm above the damper piston. Some books say the R45 and R65 up to 1985, and the LS and ST, are 35 mm +- 15 mm, above the damper piston; and the /7 and to 1984 on the other bikes, and the G/S and RT…all to 1984….are 300 mm. All this is a different way of either measuring, or of the same thing.

Further information will be found at: https://bmwmotorcycletech.info/front-fork-oils-amounts.htm 

20A. Those of you who are being thrifty and want to purchase fewer tools, may want to know of the following substitutions: 19 mm, use 3/4 inch; 13 mm TRY 1/2 inch; 11 mm use 7/16 inch. For the 27 mm locking nut on the swing arms, you are undoubtedly already aware that due to the thinness of the nut you really need to flat-grind (turning the end on a lathe is very superior) the end of the 27 mm socket. However, you may also use a 1-1/16th inch socket. You also may need to grind the outer diameter of the 27 mm or 1-1/16″ socket…and a 12 point socket may work out best.

20B.  BMW has lately been selling bolts and nuts under the original part number that have different sized heads! This may be fine for K bikes, with, for example, 18 mm heads, but this means an extra tool for an Airhead tool tray. Watch for this potential problem. I have seen it where original 19mm becomes 18; 17 becomes 16. The dealer MIGHT still have the original head sizes in the same box.

21. Due to new regulations in Europe, BMW has stopped cadmium plating many fittings. If installing studs and bolts into aluminum, be careful, you may need to use antiseize; and might need to change torque settings.

22A. Between December 1969 with the introduction of the /5 series, through most of the /5 production, BMW/Bing made some fairly radical changes in the Bing carburetors, which were ‘new things’ back then. Particularly they had problems with irregular idling, poor starting when cold, and surging. The details are too lengthy for this posting, but the particularly BAD carbs are: 64/32/3 (left); and 64/32/4 (right). The first decent updated carbs have slash 9 for left and slash 10 for right. Some intermediate carbs, without the full fixes were stamped “C” on the dome top. The author’s personal website has all the details on these early carbs in their own separate article.
https://bmwmotorcycletech.info/earlybingR75CV.htm

22B.  The proper plug to use when plugging the cylinder head smog pipe area near the exhaust port is a 16 mm car oil drain plug. Be cautious.  The author’s website has a COMPLETE article on the Pulse Air system and plugging it in various ways (and, covers the smog valves and fuel shutoff method of the last models).
https://bmwmotorcycletech.info/pulseair.htm

23.  It is possible for a really bad battery to cause the GEN (alternator) lamp to come on…so before digging really deep, check that the battery is OK, use a voltmeter AND a load tester.

24. Beginning ~1980, below the left pushrod tubes, on the engine cases, will likely be found a smoothed flat area, that may contain stamped characters. There seems to be a difference in what these characters indicate. I think only the factory knows the true story on these on the lower line of characters. In general, however, the top line will indicate the week and year, in two digits each, of manufacture, and a sequencing number following that. The weeks and months stamping have been seen reversed at times.

25.  In 1997, after seeing aftermarket oil filters I thought should never be installed,  I sent Oak (Orlando Okleshen, a well-recognized Airhead expert and official Friend Of The Marque) a Purolator and a Fram oil filter, both of the hinged type, both were sold and boxed for BMW airheads with oil coolers (the part number ends in -575). I asked Oak to determine what he…and friends and fellow engineers…thought of these filters. I’d already made up my mind, which they agreed with: NOT ACCEPTABLE!
Oak sent back quite a bit of information on the filters, recommending AGAINST the Fram. NOTE:  I have never seen common FRAM filters I liked, versus other brands.

The genuine BMW-sold oil filters are very likely good for 7-12000 miles, so you may well get 2 oil changes before changing the filter, a pain on SOME of the faired models with the coolers. Broken-in engines of reasonable mileage usually can go for these extended changes without any harm at all. When changing filters, it is a very good idea, if you have not been exposed to the information before, to read the multiple articles in our club’s publication Airmail, on: The $2000 O-ring. If you have no access to those old publications, the information, EXPANDED, is on the author’s website. Especially see articles #49 through 51D for a full understanding of the oiling system, how oils work, the problems with the canisters, etc.
https://bmwmotorcycletech.info/

26.  A common problem is to have the voltmeter on your BMW fluctuate more than normal; perhaps wildly swinging. Perhaps it drops as much as a volt or more when the brakes or turn signals are used…perhaps the GEN light glows FAINTLY at normal riding rpm..noticeable especially at night. I suggest you remove the headlight and clean the fuse contacts and fuses themselves too. Bad batteries can also cause these problems, of course. Brushes that are close to needing replacement, as well as little bits of electrical connection corrosion in the rest of the bike, can also cause these symptoms. NOTE that the BMW fairing voltmeters are NOT the same as the CAR voltmeters; they look the same, but the airhead voltmeters are much more highly dampened. Use of car voltmeters will cause them to swing madly about with use of such as the turn signals, or even road irregularities. The stock meters have several failure modes, one is wild swinging.  Another is stickiness, where tapping a fingernail on the meter causes a more correct reading.   Digital meters are available in 2-1/16″ size, that fit and work very well.

27.  Airheads built up to about 1984 need clutch spline greasing at about 15K. Going over 20K on them usually results in seeing lots of rust on the spline, a sign of wearing the spline out needlessly. Sometime around 1990 (??), BMW began plating the shaft, and 30K greasing intervals may be possible. I am not totally convinced.  There is an article on this Airheads.org website about how to clean and lubricate these splines.  Look in the alphabetical S area.

28.  If you CANNOT turn off the engine with the key…the problem is likely a shorted diode inside the HEADLIGHT relay!!  This is a VERY RARE problem.

29. Alternator brushes are about 16-1/2 mm long when new. A common problem is to let those brushes get too short before you replace them, and then the coil spring will bottom out on the brush holder, and you will begin getting strange charging problems. It is best to replace the brushes when they are around half worn. An article is on this website, but one in more depth is here:
https://bmwmotorcycletech.info/altbrushrotor.htm

30.  The factory preload specification on the wheel bearings of our Airheads with the tapered bearings (often called Timken style), used up through 1984 models except for a few R65 models, is too tight…and in practice the factory has often shipped the wheels with the preload set WAY too high. This WILL lead to worn/scorched bearings and races/shells. The worst case would be a seizure at speed. Preload measurements are made WITHOUT grease seals, and with cleaned and OILED, not greased, bearings and races. I have found that 15-25 inch ounces is best. Doing your own preload measuring and adjustment, and changing or modifying the one shim involved, is NOT at all difficult, although moreso on the earliest models of /5/6 where you must heat the wheel hub (and, 1978 REAR DRUM model). You should already be cleaning and regreasing your wheel bearings and installing new grease seals, at every other tire change. Maintained correctly, your bearings will last a lifetime.  There is a very detailed article on the author’s website:  https://bmwmotorcycletech.info/  I HIGHLY SUGGEST you read the article!

31. Genuine BMW control cables, after the first production of those cables in the very early 70’s, are lined with a nylon type material and should not be oiled or greased. DO oil/grease the end bits.  I HIGHLY recommend you use ONLY BMW-sold GENUINE BMW CABLES.   BMW has sold some cables, and may still be selling them, with BARRELS or crimped ends that do not fit properly.  File them so they work smoothly.  Use a moly oil or moly grease on barrels…and regularly.  Pay attention to the clutch lever, if it will angularly move in its pivot more than faintly, replace the nylon pivot.  Do NOT bend the left outer cable sheath of the throttle cable when checking your oil!  BTW…Oil is checked withOUT screwing the dipstick into the engine.

32.  Maintaining windshields and visors, which are made of various plastics, should be done carefully, rather than sloppily as usually done. Clean your plastic with the ring-less palm of your hand…and water with tad of liquid dish soap. Do not use a rag unless you insist. If you use a rag, clean in up and down or side to side motions, NEVER EVER CIRCULAR. Do not use solvents on the plastic…although use of kerosene or Turpentine on a rag, briefly, to remove tar or non-water soluble tree sap, is OK. NEVER use Windex or other cleaners, particularly if they contain ammonia. Some folks have been finishing a cleaning job using Johnson’s Pledge, and it seems to do a reasonable job. A better job is done by Meguiar’s, type 10 and type 17 covers basic needs. An even better job is done with some newer products, listing here:

https://bmwmotorcycletech.info/chemicalsetc.htm

The final part is applying the polish, which usually contains a small amount of a wax substance that tends to fill-in fine scratches. When applying these cleaners and polishes, be sure to use a Turkish towel type rag…a great way to use old bathtowels…and NEVER use circular motions….they can leave fine marks that will blind you when riding into the sun. For SERIOUS scratches, you have little choice: replacement, or fix. Scratches that are just feelable with your fingernail can almost always be fixed by using superfine grades of sanding paper from your hardware or paint store. I prefer “wet or dry” paper, in grades from 600 to 1600. You may have to go to an automotive paints supplier to find grades above 1000. Use light to moderate pressure, NEVER with a power tool, and use lots of water.

The author’s website:  HTTPS://BMWMOTORCYCLETECH.INFO/INDEX.HTML

Initially published in 1999, this article was updated 05/21/2013; 06/05/2014; 01/08/2016; 05/20/2017; and, on 01/12/2021.

Snowbum
ABC #1843
HTTPS://BMWMOTORCYCLETECH.INFO/INDEX.HTML