WHEEL BEARINGS AS USED ON BMW Airhead Motorcycles
Servicing and Preload adjustments on PRE-1985 Wheel Bearings.
Please refer to the author’s website for the latest information…there is a lengthy article on the wheel bearings, covering every aspect of pre-1985 bearings, and also covering 1985+ bearings in a small way.
https://bmwmotorcycletech.info/index.html
Very detailed servicing information, but not including all the verbal comments, will be found in the companion booklet “Tapered wheel bearing seminar” as delivered at the BMWMOA rally, Spokane, WA, Saturday, July 17, 2004, by Gary L. Smith and me, Robert Fleischer (aka Snowbum). There are a few typos of some modest importance in that booklet, you may contact me at snowbum@bmwmotorcycletech.info should you have that booklet and wish the updates.
Some of the verbal presented information was VERY important, and some of THAT is available on the author’s website:
https://bmwmotorcycletech.info/index.html
See the various sections of multiple items #54 on the Technical articles Index Page, especially sub-section 4.
In addition, highly recommended, are the four articles on Servicing Tapered Wheel Bearings, as done by Gary L. Smith, beginning with the May 2004 issue of BMW Owners News.
Additional reference material may be obtained from the following URL: http://w6rec.com
Inexpensive scales are available from http://www.sargentwelch.com
Suggested models are either WLS3774-F or WLS3678-DD; and there are others, similarly INexpensive, from Ohaus.
Much more detailed information on wheels, bearings, etc., is found in the Author’s website, see referenced item #54. The information is quite complete and even has a list, with sizes and BMW part numbers, for all the 17 mm and 14 mm wheel bearing spacer shims, and, of course, detailed procedures.
I STRONGLY suggest you gather ALL the information available, before working on your wheels….this is ESPECIALLY important if you have the /6 and earlier hubs. The /7 and later hubs, in particular the front wheel from 1978 (except the REAR DRUM BRAKE model of 1978) and all wheels from 1979 through 1984 (through the end of the use of tapered wheel bearings in 1984), are much simpler and easier to service.
Pay special note to the fact that early wheels had to have the hubs heated in order to do any servicing, although some quite simple modifications are in the Author’s website article that eliminates some heating except for bearing replacement. The 1978 rear wheel for disc brakes and drum brakes are very different, with the drum wheel needing heating.
These procedures may seem complicated at first, but in reality it takes only minutes, once you have done it previously. MUCH of the information will not, perhaps, apply to YOUR motorcycle, but it all does need to be read, and understood.
BMW Airhead motorcycles are relatively tolerant to abuse and poor maintenance. Our human bodies are not tolerant to being dumped on the road at speed from a motorcycle. Of all the items that are safety related, the mechanically most important are the condition of the wheels, tires (tubes if any), brakes, wheel bearings. For non-mechanical, well, of sorts, one could add the importance of the rider’s clothing, and, in particular, the rider’s condition and competence/skill.
Please do not work on your own wheel bearings, unless you understand what you are doing, and if you do not feel competent, take those wheels to a KNOWLEDGEABLE expert; or, you may want to attend a weekend TechDay, or other event, to learn. Many owners are reluctant to change a tire, let alone work in the wheel bearing area. The author of this article has no qualms about any Airhead taking his motorcycle to a competent shop; and in fact encourages you to support them. NOTE in particular…that not very many BMW dealerships have the knowledge to properly and competently work on Airheads. Many independents do. Find a good one! ASK on the Airheads E-mailing LIST.
In keeping with Airhead Canon’s #6 (Airheads maintain their own motorcycles); and, #8 (Airheads like to share time, knowledge, parts and camaraderie with other Airheads), the following is presented:
BMW had tapered wheel bearings for all models except certain R65 models, until its ‘new’ wheel series in 1985. In 1985 BMW went totally to a sealed bearing assembly that was NOT the adjustable preload type, and those bearings are replaced upon need or miles. Prior to 1985, except for the mentioned R65, BMW had used a type of tapered roller wheel bearing that is generically referred to as “Timken” style.
The inherent design of roller bearings in general tends to PARTIALLY trap the lubricant between the LARGE working surfaces which is one reason they last so long if kept clean and reasonably greased. These are the same type of bearings used in almost all old and some newer automobiles, and the same tapered roller bearings are used in our Airheads steering stems and swing arms. This type of bearing is very rugged and long lasting if serviced regularly, 250K miles is NOT unheard of. FYI, this wheel and swing arm bearing is a FAG 30203A.U.P. Any quality name brand 30203 bearing is acceptable. NO special specification tolerance is required. This bearing consists of a ‘cage’ (a holder with slots) that contains a number of hardened steel rollers set on an angle and having an inner matching part through which the axle goes; and, a separate piece, the outer race, also hardened, and machined to match the angle of the bearing/cage. Being on an angle, and with a set of these on the left and on the right side of the wheel, some means must be found to adjust the clearance of these bearings/cages against their corresponding shells/races, due to tolerances in the bearings, but MOSTLY due to differences in the mounting cavity of the wheel or in the inner spacer parts on some wheels in particular. On very old cars at least the outer bearing is usually this Timken type, and it is adjusted by means of a nut, with a locking nut or cotter key pushed through a hole(s) in the end of the axle, or some similar method. This type of adjustment and locking is not appropriate with the design of a two fork system like on the front of our BMW’s (and the 2 swing arm models too); although it is possible. There is also too much variance in how one person might adjust such a nut. Motorcycles have different types of side loading compared to a car, so a good method of setting preload more exactly is needed. BMW elected to use one variable width spacer inside the wheel hub to set the pressure/clearance (preload) on the bearings. The spacer is available from BMW in a variety of widths. As a practical matter, numerous lengths of OTHER spacers are incorporated for various reasons in the wheel hub assembly, but only one is the spacer that is adjusted by changing to a different width, normally. To answer more completely, the types of wheels, such as the rear heated hubs types, do have a very large spacer too, which can be modified by sanding, to set the preload, where you might not have proper preload spacers available easily.
BMW has used several styles of wheel grease SEALS over the years, and there is a fair amount of complication in specifying exactly which seal is used where. There is one type of seal used in 1970 through 1977 spoke wheels, rear, left side; 1970-77 spoke wheels drum brake front, left side onl; and, 1974-77 spoke wheels, disc brake, front, both sides. There is a complication over the felt and retainer used in 1970-early 1972; and a different seal is used for late 1972-1977 spoke wheels, right side REAR, and late 1972-1977 front wheels with shoe brakes, right side only….AND the seal that is used on ALL the cast wheels, 1978 and later, with an EXCEPTION, the EARLY 1978, REAR ONLY. FINALLY, a slightly different seal number is used on cast wheels on the R65…and SOME other cast wheels….AND some of these seals that are used on the cast wheels are specified for one wheel or the other….but will fit all the late cast wheels prior to 1985 anyway. On the later Airheads, prior to 1985, the snowflake rear wheel is specified for a different part number for the left and right REAR wheel seal…but, in fact, either seal works in either position.
OK, I know this all sounds VERY confusing. It is….BUT, your dealer or independent BMW shop can supply the correct seals. BE SURE you find out what seals you need. Do NOT depend on just any dealership parts person!!!! Once you have the correct type (and a few spares!!) you know which ones to get in the future! While you CAN just remove your wheel seals for the first time & read the tiny print on the seal rubber and get that part number, or one close to that number (the number ON the seal is not the exact ordering number), I do NOT suggest it except as a matter of interest…as those seals might be the wrong ones!
My personal recommendation is that you clean and regrease your pre-1985 wheel bearings every second time you install new tires!
Remember it is the seals that keep water out of your bearings (unless you point a high pressure hose directly towards them), so always replace seals.
HINT: ALWAYS install new inner tubes if you use inner tubes!
When doing the preload measurements and balancing, the bearings are first cleaned, then oiled, not greased, and the seals are first removed of course, and that means that this is the PERFECT time to balance your new tires on the rims, on a proper tire balancer; as balancing requires oiled bearings, no seals, if you want a perfect job. If you are NOT doing the preload measurement, but ARE changing tires, you should balance the wheel/tire without the seals. The BEST balance is with NO seals in place, due to the friction of grease and seals.
If you have never had your preload checked and bearings greased…DO IT!! If you are replacing a 19″ front Snowflake wheel under warranty (there was a recall, information article on my website), be aware that the wheels come without proper preload, without proper greasing!!!!!
Wheel seals are NOT really overly critical to being installed “perfectly squarely and exactly to proper depth”. You need to be close. You do not need special tools for removing and replacing seals, regreasing, etc., although tools can be helpful.
For PRELOAD measurements AND adjustments…YOU DO NEED ACCESS to a common micrometer although a good vernier caliper will do, and ONE OR TWO ADAPTERS TO DO THE PRELOAD TESTS; and these are NOT special factory type tools. One other ‘tool’ you will need is a common cheap pull spring scale. THESE WILL BE DESCRIBED IN THE PROCEDURE THAT FOLLOWS.
All the above been said, it is beyond an article like this to list every seal, and felt and retainer, and combination, as used on every model…and to try to make this article ‘one size fits all’. THEREFORE, I am writing this article to fit specifically the early 1980’s airheads, for which I have rather extensive experience in the recent past….AND…I do not have to try to remember all the little details from years ago! [BASICALLY, all our wheel hubs/bearings/seals, are quite similar, that is, there are only two BASIC types, heated hubs and not heated hubs]. I HAVE included some minor information on the 1985+ model axles, etc. There ARE differences in the wheels, hubs, spacers, not just seals and so on…so be careful to read, read on other websites such as my own, and such as Duane Ausherman’s, and ask questions.
Do ONE wheel at a time! Do NOT mix up right-to-left parts (especially the bearings). I have actually gone so far on my own RT as to lightly engrave L and R on the end of the bearings. You would be surprised to find out how easy it is to forget to keep things separated. PLEASE take the time to ENSURE you do NOT mix up left and right parts! It is PROBABLY true, that for the SAME manufacturer, you can mix up the bearing parts when brand new. This is unwise though, and it is very unlikely to be OK if the bearings are used.
The first time you do this procedure, take the wheel seals to your BMW dealer (or other knowledgeable expert) and have them match them with new ones, and have them crosscheck against their parts information. You will find that the wheel seals have a number that looks very similar to a regular BMW stock number, molded right into the rubber, on the inside of the seal. Have them double check that the ones you removed were REALLY the correct ones for your machine. If they do not know the truth, ask on the Airheads LIST!!!!
The seals are installed flush and flat with the hub, and I would say that the maximum tolerance you should TRY FOR is one or two thicknesses of a common matchbook cover, either too far in or out. Flush is best. It is NOT overly critical. The axle should be clean and greased. If the axle is badly corroded or rusted, clean it with fine sandpaper, but clean it and grease it lightly after using sandpaper. You want the axle to slide easily into the spacers, bearings, and swing arm.
There is the possibility that you could find a bad bearing. They are NOT difficult to replace, and are replaced as two matched parts (bearing/cage and outer race); and it is wise to do both sides of a wheel at the same time; that is 2 complete bearings you would need. You MUST set preload after replacing bearings. Replacing bearings is simple on the later airheads (to 1984) but more complicated on the ones produced in the seventies…..which usually require heating, and precise fitment of the bearings and various spacers, including a large diameter spacer, all as one assembly, with the wheel HOT.
I have seen postings to the AIRLIST wherein someone questions as to heating or not heating the wheel hubs. GENERAL RULE: the outer races are made of steel; if they are fitted into a wheel that ITSELF has a steel insert (usually the insert is cast into the aluminum or magnesium wheel hub, and needs to be eyeballed to see it), then the shells/race are PRESSED OUT, as heating would expand the steel insert and the bearing outer race at approximately the same rate, doing nothing, but probably not damaging anything either. Restating: the outer race is a press fit into a wheel’s STEEL hub. IF there is NO steel insert cast into the wheel hub, then the hub is heated, gently, in circular motion to avoid spot heating. Some wheels have a captive insert in the middle of the hub that may have a plastic part…don’t heat that! For the type of wheel with NO cast-in steel part, the wheel hub aluminum alloy will expand faster than the steel outer race, and that outer race will come out easily (actually, we remove the whole innards assembly at one time). For the most part, the 1970-77 (some 78), wheels were aluminum hubs and ARE to be heated to replace bearing shells, while the later ones have a cast-in steel hub and are NOT heated. SOME early wheels bearings will NOT just drop out. As Matt Parkhouse posted on 26 July 1999, you use the rear axle and a 4 inch length of 3/4″ common pipe as tools and heat the hub. Please refer to that procedure as posted by MATT…or on this author’s website.
When installing the wheel, don’t overtighten axle nuts, the factory book figures are on the high side, in my estimation. This is more critical on the hubs that are heated for bearing work, and especially on the /5 wheels.
Most BUT NOT ALL wheels are fairly similar front and rear. EARLY wheels are quite different, front and rear. There is likely a captive insert on later wheels (that is, it remains internal to the wheel when the shells/races are in place, so do not worry about any ‘loose spacer things’ inside the hub).
When you reassemble a wheel, do not forget to bounce the fork…just jump up and down on the bike…before tightening the pinch bolts, to help centralize the wheel in the forks (clean and lightly greased axle!) and swing arms. Failure to do this will cause fork stiction and can INJURE the rear drive. If the axle is not a smooth easy fit in its clamping area, clean it up, & lightly grease it. Do NOT make the mistake of tightening clamping nuts before tightening the axle nut; for the front wheel it can distort the distance between the tubes and cause stiction; for the rear wheel it can cause serious damage to the rear drive.
NEVER EVER rest a disc brake on the floor while you change a tire or work on the wheel. Bending a disc, easy to do, will cause braking problems, and replacing a disc is not cheap. Best to use 2 (or 3) 2 x 4 pieces of wood to support the wheel/tire. DO NOT EVER hang a brake caliper by its hose!!…you can ruin the hose internally.
The following is what you would expect to find on a early 1980’s Snowflake wheel; looking at your front wheel, FACING FROM THE FRONT:
Axle with its hole comes from the left, passes through the fork leg, through the seal, through a lipped metal spacer with the lip INWARDS, then the bearing, then the wheel with its hub and internal captive spacer and then the preload spacer.
Let’s stop here, continuing later….and discuss that preload spacer. It is common to hear of it called a “wedding ring”.
Only ONE spacer is changed (or modified) to change the preload on a front wheel, and if it is not in the size range shown here, it is NOT the preload spacer, as no other spacer comes even close to this one in size (width). The preload spacer thickness (width) ‘sets’ the preload on the bearings. The spacers come in many sizes, and for 17mm axles are in the range of approx. 0.248 to 0.2835 inch. For the early wheels, like the /5 14mm axles, the range is approximately 0.378 to 0.4016 inch. If the preload is not within specifications, you have to MEASURE the width of the existing spacer so you can make an educated guess at what size spacer to change to. Almost always, unless you are installing new bearings (with outer races too, of course), a ONE step change in size is the most you might expect. In some cases you can CAREFULLY narrow one by sanding on a flat surface. To measure the width, you need an ordinary micrometer that is relatively accurate to a few ten-thousandths of an inch. You should be able to borrow one of these, and be sure to use it properly; they are not to be used by people who like to tighten things a lot, they are used gently. Common ‘vernier calipers’ are sometimes NOT accurate enough! [yes, I know that there are SOME that are available that ARE accurate enough]. The MAIN thing about the micrometer and vernier is not absolute accuracy but repeatability between measurements.
Back to the FRONT wheel, facing from in front of the bike: After passing through the preload spacer the axle proceeds to pass through the bearing on the right side of the wheel, another lipped spacer with the lip inwards as before, the seal, and an approximately 3/4 inch wide sleeve spacer, then the fork, then the lock washer, and then the axle nut. Some wheels have caps and slightly different spacer setups.
For those of you who are curious, it is conventional practice, facing the front wheel, for the disc brake bolts that hold the disc(s) to the wheel, to be inserted from the left….that is, the NUTS are on the right. I mention this as the wheel might be reversible, and you really do want it back the same way for those dual-disc front wheels. Why?…well, to mate the discs and brake pads is just one reason. Also, some tires are directionally marked, and even if not, you’d not want to reverse the wheel after some miles on a tire.
Rear wheel: pretty much the same, for dual-shock bikes as you face the rear wheel from the REAR. However, the EARLY rear wheels have two possible adjustment methods, the so-called wedding band, and there is also a much larger long sleeve. Sanding one is opposite in effect to sanding the other. That long large cylinder sleeve spaces the two bearing outer races!
For most twin swing arm (dual shock) Airheads, the preload setting spacer is on the left side of the wheel of the inner wheel hub area. There is one different item of minor note: The LIPPED spacer on the RIGHT side, as you face from the rear, is normally a 9.2mm wide spacer. If you fit a some 110-90/18 tires, or nearly every 120-90/18 tire on the rear, instead of the stock 4.00-18, AND you have a 1981 or earlier snowflake wheel….you MAY have to change to a 36-31-2-301-737 lipped spacer, which is 10.7mm wide, which spaces the wheel very slightly (only about .060 inch) to the left, to help maintain clearance at the swing-arm cutout. You might find this already done. I have seen numerous 1981-1984 wheels requiring that spacer too, some on even 110 tires.
Once you have removed the wheel from the motorcycle, the next thing to do is to remove any trim or whatever [on some models], to gain access to the seals. The seals will have a lipped spacer sticking out from the seal. The lip of that spacer is INside the seal! You can use a round rod or large screwdriver to pry that lipped spacer right out through the seal…which of course destroys the seal, which is of no matter, since you will be replacing it anyway. DO NOT stick that ‘tool’ in too deep…that will scratch the hub. REMEMBER!…. on some machines these lipped seals are different, right and left…so now is a good time to MAKE NOTES or sketches…and continue to do so throughout the process. NEVER trust what the previous owner or mechanic has done!! Always double check that the correct seals, etc., are on your bike when you are finished. With the lipped spacer removed, you now need to remove the seal. You can use a real honest-to-God removal tool, or the fat round rod from the Airhead tool kit, or simply use a large screwdriver. I prefer to modify an old spare large screwdriver for this job. I prefer to round the tip corners in both directions (sides, top and bottom). This is to HELP avoid scraping the hub. Just do not stick it in very deep. When removing the seals with a screwdriver you simply place the screwdriver through the seal hole a small amount and USE A SMALL PIECE OF WOOD OR?? under the screwdriver metal shank, as to set an angle better to pry against the hub with, and pry the seal out. The wood also protects the wheel hub exterior from scratches.
As soon as the seal is out, the inner part of that bearing is easily removed with a fingertip.
Note: When you replace the seals later in this procedure, you oil or grease the lipped spacers and fit them FROM the inside of the seal, before pressing the seal into place. New seals are easily pressed squarely into place by using any old socket that has an outside diameter that is NOT MORE than about 3/16″ smaller than the seal diameter, and preferably almost the same diameter. You use a hammer, gently, on the socket, watching to keep the seal going in squarely. If it begins to go in cock-eyed, you simply angle the socket a tad and hit gently. Seat the seals to flush or not much more than the thickness of a matchbook deeper than flush.
If you are simply inspecting and then doing a grease job on the bearings, with fresh seals of course, you only need to leave the bearing in place and rotate the bearing center area by hand, while applying some pressure towards the interior. NO roughness, however slight, must be felt. Inspect the bearing and its in-wheel shell (outer race), for scorching, overheating (yellowish brownish and overheated metal appearance), and scoring marks. These, and roughness felt, are generally cause to replace the bearings/cages and shells/races. If you do not know what amount of discoloration or ‘look’ is acceptable, ask a QUALIFIED mechanic to look at them.
Assuming your bearings and shells are OK, you force grease by hand or a bearing greasing tool, throughout the bearing, add some to the race and cavity (clean out most of any hardened or dirty grease first). Then install the appropriate lipped spacer, oiled, into the seal from the inside, install the seal with the lipped spacer. Now do the other side of the wheel, and reassemble the motorcycle and go for a ride. Any good grease sold for use as disc brake grease is acceptable.
If you are doing a full job, which means doing the preload check, the bearings are to be 100% cleaned in an appropriate solvent, such as kerosene. The preload check is done withOUT seals in place and WITHOUT grease, ONLY OIL! Once the bearings are very clean, dry them, and then OIL them (almost any oil), and install the bearings in the matching side of the wheel, together with the spacers, etc., that you removed previously. The ONLY parts NOT to be installed are the grease seals. This full job is usually done by me at tire change time, so with the bearings still OILED and no seals installed, I can do the balancing, and then preload work…and then do the final cleaning (of the oil, etc.) and greasing and fresh seals.
At this point, I will describe the preload, and how it is basically measured, and the 1 or 2 special adapter tools needed.
When the proper width spacers are present in the wheel hub, the wheel is mounted normally in the motorcycle, and the axle nut tightened to a point slightly near normal torque, the force from tightening the axle nut tries to squeeze together all the parts mentioned. A very tiny amount of free play must exist to allow the wheel to turn without substantial friction. If this free play is much too low, meaning tight bearings, frictional forces in the bearings will squeeze out the lubricant, overheat the bearings, and in an extreme case, will actually weld the bearing and shell together. This could cause an accident if it occurs suddenly and without warning, sometimes there is no nasty sound or none until the fateful moment. If the free play is excessive, you will have instability in your steering. Of the various types of instability possible included is a high speed wobble, a rather unpleasant affair; as well as various other problems such as unstable feeling, tire cupping or other wear types, etc.
BMW specifies a certain preload, and what this preload actually is, is the force it takes to turn the wheel, bearings oiled, seals removed, axle in place and axle nut torqued to the specification. This is difficult to measure with the wheel in place in the forks…although it could be done, and I have, in fact, done this by measuring the pull on the tire circumference. That is not an easy nor very accurate measurement, hence this procedure spells out a better one. Since our motorcycles that have wheel bearing preload spacers also have forks, two in front and in the rear, and the wheel is not in those forks when this force is to be measured, then we need some sort of spacers to be made in a machine shop, to take the place of those fork(s). Luckily for snowflake and most other wheels owners, only one or two spacer tools need to be made. These spacer tool(s) are usually used, on most models, ONE per wheel, sometimes using the existing small axle spacer as needed, and these spacers are fitted on the axle with the seal-less wheels, axle nut tightened, wheel out of the bike.
In specifying the spacers to the machinist, who will make them for you, there are a few factors to be considered.
The spacers length must be such that they replace the width of the fork(s), yet are not so long that when in use you cannot fit the axle and axle nut through the entire wheel assembly and the spacers being manufactured by your machinist.
The inside diameter of the spacers must be the same as your axle, plus ABOUT a thousandth or so more. To get a really accurate preload, the spacer inside bore should be very SMOOTH, and a fairly good fit, but NOT a push force fit, on the axle. Therefore, you need to supply your machinist with your axle and specify a just smooth fit, with a minimum of play, oiled. The end faces of these spacers MUST be flat and square to the bore. Because of this, you should not consider making these spacers yourself, unless you have a lathe.
The material should be steel. Stainless steel is NOT necessary.
The final specification is the outside diameter. This is to be selected carefully for TWO reasons:
The correct outer diameter means easy mathematical calculations for preload.
The correct outer diameter is one that fits (presses against) the bearing, but not so large that it overlaps the bearing and presses on the hub; nor, so small that it does not press on the proper part of the bearing.
I have one set of these spacers which I use in my shop with the snowflake wheels. One is approximately 3-1/8th inches long and the other is approximately 2-1/4 inches long. The two spacers allow me to do preload work on both front and rear wheels. The diameter I am using is 1.50 inches. You can specify them in lengths and diameters YOU want. I suggest you DO use the 1.50″ diameter. These sizes worked fine for all snowflakes wheels, and many others.
To check the preload, you simply assemble the wheels with OILED bearings, one spacer tool on one side of the wheel, and all the parts in place as required except the seals, and tighten the axle nut (which needs to be only maybe 20-25 footpounds for the preload check, or you can use the standard 30). You now wind a piece of common string around the spacer tool, perhaps a dozen turns or so, in ONE layer. You attach a pull-scale of the spring type [cheap ones do just fine] to the end of the string, and SMOOTHLY pull on the scale until the axle starts moving, and you read the scale while the axle is moving SMOOTHLY. If the spring scale jerks (it will, some, in any event) really badly, with 30% or higher changes during the pull after movement begins, then you have bearings that are totaled, and you did not check them properly; OR you left the seals in place; OR, your adapters are machined with excessive play or faces that are not square.
You need to convert the spring scale reading, and that is all there is to the process, except if you need to change [or modify] the preload spacer.
Specifications on preload, ‘By the Book’: 21-42 INCH-OUNCES. I feel strongly that 42 in-oz is MUCH too high, and tends to scorch bearings. I set my own high limit to 30 INCH-OUNCES, and really prefer around 15 to 25 INCH-OUNCES. If you see figures published someplace in metric numbers and see the figures as 1.5-2.5 CMKp or 15-30Ncm; and those are fine too, although the conversion is not the same as my liking, which is that 15-25, limit 30.
In my shop, I have pull scales graduated in grams. For 1.50 inch diameter spacers, the pull force I would like for you to use for 2 wheel Airheads (no sidecar) is 567 to 943 grams. For the original factory specification of 21-42 INCH-OUNCES, the force is 794-1588 grams. Again, I emphasize that I do NOT like the factory spec! In some BMW shops, they don’t even measure the preload, using a ‘feel’ for the play, usually after assembly, and I am NOT in favor of that, but it WILL work with a very experienced mechanic. I DO use that method as a quicky check, and especially on the /5 wheels.
The formula for the multiplier factor,,,(unless the spacer is exactly 1.00 inches in diameter, which does not work for our size bearings)….is: inch-ounce specification divided by the RADIUS (that’s half the diameter, folks!) of the adapter spacer. I suggest that you use 1.5 inch diameter spacers, unless you have wheels that won’t allow this; with 1.5 inch diameter spacers you need not calculate anything, just use my gram figures.
Forget about calculations for the diameter of the string. Just don’t use rope! The string that works best is light cotton or nylon packaging twine, or inner parachute cord.
For reference purposes, rounded values:
16 ounces = 454 grams
1 ounce = 28 grams
NOTE: Your dealer has a chart (parts book, CD, or microfiche) that lists all the different sizes of the preload spacers that are available, for both sizes of the axles in use. The chart will show that each next size up in wedding band spacer is APPROXIMATELY 0.002 inch thicker (wider). SOMETIMES (maybe often, actually) a change of 0.002 will be just too much and the bearing will be too tight or loose. If you use a wider spacer, the preload DEcreases, as the bearings are now ‘held out’ farther from the bearing shells (outer races). If you cannot find the correct spacer width, get one a step too wide, and hand sand (on a FLAT surface plate with very fine grit sandpaper, in figure eight’s) until it reads correctly on your micrometer. Be very careful about sanding. The end surfaces of the spacer MUST remain flat and parallel, and square to the bore, and the ends SMOOOTH. My website also has every one of the shim spacers listed in a chart, clickable from my own in-depth wheel bearing article.
Once the preload is within specifications you’ve decided upon, you must remove the bearings, remove the oil with a solvent, dry the bearings, and hand grease them thoroughly through and through, and add extra grease to the cleaned hub bearing area. Then, just as described previously, install the oiled lipped spacers into the seals, install the seals using an old socket upside down, and reassemble the motorcycle in the usual manner.
Repeat the process when you install new tires. Once you have done the procedure once, you will find it takes only a few extra minutes and will reward you with very long bearing life.
I have over 580K on BMW’s, and have NEVER had to replace a wheel bearing in a BMW airhead that I purchased and serviced from new, probably because I replace seals and regrease, at every tire change….although one of my R60 machines was close to it when I sold it at about 274K. I have seen brand new BMW’s right out of the crate, with excessive preload…WAY excessive.
NOTE: While this procedure as written applies particularly to the early eighties wheels, the very early wheels that require heating to remove the entire innards, will have, on the REAR wheel, a LARGE cylindrical spacer. That spacer can be sanded, or the wedding ring sanded, depending on what effect you need. HINT!…these old early rear wheels have a FINNED spacer inside. I suggest you grind the fins a bit, so that the fins will easily come out to the left, so you can do some future greasing and adjustments without heating the hub. NOTE that on these early rear wheels that you HAVE TO remove the ENTIRE package of contents as one unit, after heating the hub, using the axle as a tool for that. See Matt’s article on this website.
Please refer to the author’s website for the latest information…there is a lengthy article on the wheel bearings, covering every aspect of pre-1985 bearings, and also covering 1985+ bearings in a small way.
https://bmwmotorcycletech.info/index.html
Snowbum
Originally published in 2004; Revised completely 10-30-2007; updated 02/26/2013; and minor updating on 05/21/2013 and 06/05/2014 and 05/22/2017
and 02/21/2021.
Copyright 02/21/2021, R. Fleischer
