BMW motorcycle wheel bearings

Section 4: Wheel Bearings; preload & servicing

NOTE: Please see this URL, and read the wheel bearing information completely through, BEFORE you read the rest of my article. http://w6rec.com/duane/bmw/

Duane and I do not see things EXACTLY the same way, but his article on the wheel bearing preload is now very extensive, and his SHAKE method is one I use myself now and then.

NOTE, that while I do not totally agree with Duane's information, it is good reference material, and he has a different way of presenting some information.

Part 1: General discussion

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 most important, in my mind at least, is YOUR condition, and somewhere in the next position(s) is the condition of wheels, tires, brakes.....and maybe wheel bearings. Please read this Section completely through, and THEN decide if you are competent to do this work. NOTE that working on wheel bearings and preload is serious business. HOWEVER, IT IS NOT ALL THAT COMPLICATED, AND SOMEONE OUT OF THE BEGINNER CATEGORY, AND INTO LOWER MIDDLE OF KNOWLEDGE, CAN SERVICE THESE, WITH NO PROBLEMS. MAYBE EVEN A BEGINNER WHO FOLLOWS INSTRUCTIONS!!

Failure to properly maintain wheel bearings (and their preload, up through 1984 models) (BMW switched to ball bearings in 1985) can be hazardous to your health. A seized up bearing, at speed, is serious.

BMW used (up to the change to sealed ball-bearing assemblies in 1985, see near end of this article, in PART 4, for a possible anomaly with the R65LS front bearing of, perhaps, 1981) a bearing that consists of precision ground and hardened rollers set in a cage, that caged roller unit is set on an angle to exactly match its mate, a hardened and precision ground outer race . This design was used for the wheel bearings (and, in the /5 and later, also at the steering head; and, the swing arm bearings are basically the same as the wheel bearings ). This bearing is often called a Timken bearing, although that is a trade & company name. Those same type of bearings, but larger of course, were used in almost all old automobiles and trucks. This type of bearing is very rugged, long lasting if serviced regularly, and 250K miles of use is NOT unheard of. With proper and regular servicing, they will not generally suddenly fail without you seeing a problem developing during an inspection and servicing. The bearing in our airheads wheels and swing arms is a common type 30203A, which is 17 mm x 40 mm x 12 mm, available at any bearing supply. Bearings and their associated outer race come as a matched set and should NOT be mixed up. #30203, not-A, can be used. I prefer the UNsealed bearings at both places.

The R65LS used a ball bearing, it is #6203, 17 x 40 x 12 mm. From 1985 the Airheads used a #6005 bearing, which is 25 x 47 x 12 mm. There is a crossover on the R65LS at 1985-86, but very apparent when you see the wheel.

Being on an angle, and with a set of these bearings on both the left, and right side of the wheel, some means must be found to adjust for some known clearance, or loading, preload if you will, for them to operate against their outer race (the ring). In our BMW airheads, the bearings are set into the wheels with the small end in first.

If the preload is way too tight, the lubricant will be squeezed out as the bearings rotate, metal to metal contact will then occur, the bearings will get very hot....and just might weld to each other at a most inappropriate time. You may or may not get any advance notice from noise, etc. If the preload is way too loose, the wheel can move sideways, and angularly, and you will have poor handling, that can lead to high speed wobbles. Bearing manufacturer's specify static loading (preload) and if a bearing's preload is within the manufacturer's range of acceptable values, the bearing has EXTREMELY long life. If the lubricant or preload is wrong, either too tight or too loose, the bearing life is shortened.

The inherent design of roller bearings tends to PARTIALLY trap lubricant between the surfaces. On most of the old cars and trucks, at least the outer bearing is usually this tapered Timken type, the inner might be the same (or another type of bearing, perhaps a ball type). In any event, the adjustment on the old autos and trucks is almost always by an adjustable nut on the end of the axle, with a safety lock nut or perhaps a cotter key, pushed through a 90° hole near the end of the axle. This type of adjustment and locking is not appropriate with most telescopic fork systems, nor the swing arms, although it IS possible to design them to be adjustable in some similar fashion.

Proper preload is NECESSARY. It is best done, unless you have a fair amount of experience, with NO seals in place, and the bearings cleaned and OILED, NOT greased. If you are using a modern non-melting 'thin' grease, and NO seals, you can, with experience, do preload by FEEL, as you progressively tighten the axle nut. Then you can add the seals. Actually, it is quite possible to do it with the seals in place. However, if you do this preload check in this 'feel' manner, DO get advice if you are not experienced, and DO NOT do this if the hub parts are quite cold. NOTE that this article uses spacers that press SQUARELY against the inner race of the bearing, and a string and string scale is used, and this method is VASTLY more accurate than the 'feel method'.....it is also very repeatable in accuracy.

BMW has used a number of internal designs for the wheels. On all the pre-1985 wheels, the preload is to be set by the thickness of one spacer inside the wheel hub. However, /5 and many /6 wheels also have a large diameter internal sleeve, that sets the distance between the outer races when the outer races are being installed. Once set, that should not change, unless there is a problem with an outer race, or someone very grossly overtightens the axle nut.

Other spacers are inside the hub, perhaps totally captive with the outer races in place, but only the one relatively narrow one is available in a number of widths. That narrow one is usually commonly called a Wedding Band. NOTE that a change of a single thousandth of an inch will have a considerable effect on the preload. Two hole sizes were used on these spacers. Up to 1975 the axle is 14 mm, and from 1975 the axle is 17 mm. On the early 14 mm assemblies, one can remove the bushings and go to 17 mm...but this article is not about such things, and it is a bit more complicated than just that. The 14 mm axle was changed to 17 mm as some bending of the 14 mm axle was noticed under severe usage. BMW had a kit for converting the 14 mm axle setup to the internal 17 mm. Again, that is not part of this article.

There are a vast assortment available of these preload 'wedding ring' spacers. However, the ones that are typically needed are few. For the 17 mm axle units, the entire assortment available varies from 0.248" to about .300" (6.30 to 7.70 mm); for the 14 mm axle units, they vary from 0.378" to about 0.416" (9.60-10.20 mm). I have seen tiny errors in some of these wedding bands as received, about half a thousandth of an inch. There is no need ( I think?) to publish a long chart showing the order numbers and sizes, here. These are available, in general, in 0.05 mm steps (about .002").

HINT: Since the full procedure means the bearings were cleaned and OILED, and the seals REMOVED, this is the perfect time to balance your new tires on the rims on something like a Telefix stand.

HINT: If you are NOT doing preload measurement, but ARE changing a tire, you should BALANCE the tire/wheel with the seal removed, to reduce the drag. Since that ruins the seal, why not just do everything at this time! I do the preload and balancing at every tire change, and always install new seals, whether or not they look OK..

The wheel seals are not overly critical to being installed squarely and exactly to proper depth. You do NOT need special tools for removing and replacing the seals. For the FULL procedure (not the FEEL procedure) you DO need access to one precision tool...a good micrometer, and probably a pair of very simple steel adapters that you can have a friendly machinist make.. You also will need a pull spring scale. You can try the Sargent-Welch company for spring scales. One rated at 2000 grams and also with ounce readings are OK, such as type 8004; which is NOT expensive;...or, you can get whatever you particularly prefer. The adapters will be fully described later herein. NOTE!....what you do is to essentially set the preload while the wheel is off the bike, using the axle and nut. Thus, you may need some spacers to take up where the fork, front or rear, was on the axle, and it is these spacers we are talking about as the adapters....and if you make the diameter a convenient value, then they fit the inner race of the bearing properly and also make for very easy calculations! ...and it would be nice to have just one or two to cover both your front and rear wheels.

HINT: Do ONE wheel at a time. Do NOT mix up the parts from left to right in that wheel!

The first time you do a preload procedure, take the wheel seals to your BMW dealer and match them with new ones, be sure to purchase an extra or a few extras. I DO suggest that you make sure the previous owner put in the correct ones! Look at the molded number in the inner seal area; but there may be none, or a part BMW number, or a nonsensical number....but the dealer's parts CD will have the up to date information.... PROVIDING the parts person knows how to interpret what he sees on his screen!

Seals are installed flush and flat with the hub, a teeny bit inward won't hurt anything. I try to install them flush or to within the thickness of two common matchbook covers inward. Note that there are also NON-metal-cased types of these seals, I am not a fan of them, they can be (sometimes) harder to put in properly/squarely, but they work fine. I install the seals using the appropriate sized tool box socket as a driver. Appropriate sized means almost the outer diameter of the seal. There are a few types of seals, but, in general, they all mostly fit all the wheels, no matter what the books say...but, this is NOT universally so. If the seal starts going in canted, put the socket on an angle too, and straighten the seal out so it goes in squarely. The proper sized socket is one that is not quite the wheel bore inside diameter.

The axle must not be rusty and pitted. If it is, clean it up. The axle is LIGHTLY GREASED during FINAL assembly just after the wheel is put back in the motorcycle. I have the axle lightly greased or oiled during the preload procedure, simply to have the axle slide in easier.

There is always the possibility that you could find, after cleaning, a scorched bearing and/or bearing race. Mind the information about heating and not heating, and pressing out...or not.... the parts. If one bearing is bad it is probably a good idea to also replace the opposing (other side of the wheel) bearing/race, and preload changing is a MUST if even one bearing is replaced. A 'bearing change' means an outer and matching inner set of two parts.

Although much of this information was in earlier Sections, I am going a bit deeper in this Section on the races:

The outer race is made of a specially hardened and ground steel, it fits into either an all alloy hub, OR an alloy hub that has a CAST-IN steel insert. IF the wheel does NOT have such an insert, then the hub, being all alloy, MUST BE HEATED, gently, in a circular motion to avoid spot heating (or a hot plate with top protection) in order to remove an outer race....and/or inner parts on some early models that might need to come out. Heating expands the all aluminum alloy hub far faster than the steel outer bearing race. You can use a hot plate with thin metal cover, ..... if you use some sort of gas torch, be very careful NOT to over-heat small areas.

NOTE!::: On the later wheels, the outer race must be removed mechanically, and the hubs are NOT heated for this. You can contact Ed Korn for a clever tool for removing the wheel bearing outer races (works also for swing arm bearing outer races); or, have any mechanic with the correct puller...even a dealership!...do it for you. For those with larger wallets, the best tool is still the Kukko puller, which works lovely in such blind holes, where the inner edge of the outer race is not easily grippable...usually due to it having the same diameter as the surrounding supporting metal. The Kukko needed is #21/5, used with the #22/2 'bridge'. If you get the 21/6 puller, same bridge, you can do the steering head bearings in the same manner. The Kukko tools are very expensive.

The 1970-1977, and some 1978 wheels, were all aluminum and ARE to be heated. The REAR 1978 drum brake wheels (snowflakes) ARE going to be the heated-hub type. The 1978 DISC brake rear wheel had cold-pressed fit outer bearing races. Front and rear shoe brake wheels have the bearing assemblies coming out as a unit from the left side. For front wheels with aluminum hubs, and disc brakes....bearings come out their respective sides, and are of the heated types. You will not injure a cold-pressed hub by heating, just no reason to do so. For a heated-hub type, NOT heating will likely damage the wheel.

****How can you determine, for SURE, what type wheel you have? steel insert? all aluminum alloy? On each side of any wheel, simply remove a seal, put a small magnet onto the inside of the hub area, but away from the outer race. If the magnet is attracted to the hub inside diameter near the outer surface, then you have a cast-in steel insert, that the bearing outer race is PRESSED in to. Usually, however, you can SEE the cast-in steel insert.

This is as good a time as any to give you a caution! Those with front DUAL discs have an option, which way does the wheel go into the bike? It is standard for the nuts holding the carriers to be on the left side as you sit on the bike. But, the important thing is to NOT reverse the wheel....so mark the hub with chalk or even engrave it, left, right. Failure to do this MIGHT result in very uneven matching of the brake pads to the disc, and you will have less braking, possibly WAY LESS, until re-broken in.

1979 to 1984 are the cold pressed wheel types.

A more complete discussion of the various hubs is in another article on this website.

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MIND the Section #2 on the early wheels!

For reference information, snowflake wheels:

Front and rear axle nuts, 22mm, 32-34.5 footpounds

In case you are curious, the 1985+ axle nut is 77 footpounds, and the release bolts are 24 footpounds.

Pinch bolts on axles, 12 footpounds.

Brake calipers to the forks, book 22.5 footpounds (I use 20, or quite tight on a hand L shaped allen wrench).

25.4 mm is 1.00 inch

.03937 inch is 1.00 mm

When you reassemble a wheel to the motorcycle, do not forget to tighten the axle nut, and THEN bounce the fork, or rear end, before tightening the pinch bolt(s), to help centralize the wheel in the forks or swing arms. Failure to do this may cause stiction in the front forks, especially annoying over small road irregularities; and some rather expensive repairs to the rear drive. Having the axle lightly greased not only protects and lubricates the fitment, but ensures the forks/arms move as required during the bouncing.

NEVER EVER rest a disc brake rotor on the floor while you change a tire or work on the wheel. Bending a disc, easy to do, will cause braking problems, primarily pulsing, and disc replacement is not cheap. Use 2 or 3 old pieces of 2 x 4 lumber to support the rim/tire, or use an appropriate fixture, perhaps an old service station oil or lube drum/barrel.

Part 2: Some details

The following is what you might expect to typically find on an early 1980's snowflake wheel....looking at your front wheel...facing from the front!!!!:

The axle, 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(s) and then the preload spacer.

At this point, I will stop here and discuss that preload spacer.

ONE particular spacer per wheel is changed, or modified, to change the preload, and it is COMMONLY called a Wedding Ring. The size range for the two axle sizes has been previously noted, particularly in another article on this website. If you are not replacing bearings, it would be UNUSUAL to have to change more than ONE step in the chart sizes for this preload spacer.

An existing preload spacer that needs to be a wee bit thinner can have that done on top of a piece of silicon carbide paper of relatively fine grit, said paper upside down, working grit upwards, and that paper is on a flat plate of some sort...such as a piece of glass. Do NOT use a soft or irregular surface. Figure eights with a hard piece of rubber pressuring the wedding band straight down, or your finger, changing positions often, will do the job. You MUST keep the faces flat and parallel with each other. You need a good micrometer to measure the width change. Micrometers are NOT to be used by people who like to tighten things a lot....finger-tip GENTLE is the word here. If your measuring tool is not accurately repeatable, to under .001", it is not adequate for this job.

OK...back to that wheel again. After passing through that preload spacer, the axle proceeds to pass through the bearing on the right side of the wheel (you are facing the wheel, remember), then another of those lipped spacers with the lip inwards as before, then the seal, and then an approximately 3/4 inch wide sleeve spacer, then the fork, then the lock washer, then the axle nut.

It is conventional practice, if you are FACING THE WHEEL as mounted on the motorcycle, for the disc brake bolts that hold the disc(s) to the wheel, to be inserted FROM the left, and the nuts are on the right. Dual disc brake wheels may be reversible, so you might not only want to remember how your wheels are done, but perhaps do as I do, I etch or engrave L or R on the the respective sides.....NOTE HERE that THIS means conventional L and R...that is, as you sit on the bike. I do that etching or engraving on the hub where it is not readily noticeable.

For most wheels, the preload setting spacer is on the left side of the wheel, as you sit on the bike.

NOTE: The LIPPED spacer on the RIGHT side of the REAR wheel is normally 9.2 mm wide (0.362"). If you have mounted an oversize tire on the rear, especially a 110 or 120 tire on a 1981 and prior bike, you might have fitted the 10.7 mm spacer (36-31-2-301-737) as noted earlier in this article. This spacer only moves the wheel to the left about .060", to help the possible interference at the swing arm cutout area. Even on the later twin shock models...well into the early 1980's....some 120 section tires will not fit with adequate clearance, spacer or not....and a few 110 tires are too wide also.

Part 3: In depth

1. Obviously the first step is to remove the wheel from the motorcycle, and if a front wheel, mark the hub left and right...and then remove any trim or cap (on some models), to gain access to the seals. The seals will, on most later models, have a lipped spacer sticking out from the seal. The lip of that spacer is usually INside the seal. This is not so on some early models. There are so many variations! Main thing is that the spacer press on the center part of the removable inner bearing. It is probably a moot point, but a lip on some can be put on the outside, for extra spray protection...or some think. Engineering-wise, I prefer a lip press on the entire inner race. Depending on the wheel type, use a round rod or large fairly blunt screwdriver to pry that lipped spacer out through the seal...if the lip is inside. This destroys the seal, but you are replacing it later anyway. Don't stick the tool in too far, don't scratch the inside of the hub, and REMEMBER that SOME wheels use different size spacers left and right, so mark them or keep notes! There is an official seal removal tool at autoparts stores you can buy if you really think you need another tool. I use a thick, broad, rounded edge, screwdriver. CHEAP CHEAP...yep.

Later, when you install new seals, you will first install the OILED spacer from the seal inside (except some early wheels are reversed). New seals are usually tapped SQUARELY into proper position by use of a hammer or mallet and an appropriate size of socket...the outside diameter of which is not more than about 3/16" smaller than the outside diameter of the seal. Gently, slowly! If the seal goes in cocked, tilt the socket. Seat the seal to flush. Do NOT hammer on that socket such that you damage the hub nor seal...be sure the socket is not hitting the hub. It is CRITICAL that you do not carelessly nick the inner sealing surfaces (knife edges, or so called, and may be one or several) of the seal when installing a new one.

2. With the lipped spacer removed, you now need to remove the trashed seal. The same tool will work, insert just far enough and protect the hub inside diameter and the outside, and give the tool a good whack, and the seal will go flying out. Protect the hub exterior from marks by using something like a piece of wood under your prying tool.

3. As soon as the seal is removed, the bearing is removable with your finger. This is not so on the right side of some early wheels, so there are variations.

4. If you are simply inspecting and then doing only a grease job on the bearings, with fresh seals of course, you need only to leave the newly greased bearing in place and rotate the bearing center by hand, whilst applying some downward pressure. NO roughness, however slight, must be felt. Remove the bearing and inspect the rollers and the outer race. On early models with the more captive right side rear wheel bearing, at least FEEL the rotation. Watch out for scoring or overheating (yellowish-brownish and overheated metal appearance). These, and any roughness felt, are generally cause to replace the bearings and outer race. Ask a knowledgeable mechanic if you are not sure.

5. Assuming your bearings and races 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). Now install the oiled or greased lipped spacer from the seal inside, and install the seal/spacer via the proper socket, squarely, and to flush. Do the other side of the wheel, reassemble the wheel to the bike, properly doing the bounce test after the axle nut is tight, tighten the axle clamp bolts, check things over, and go for a ride. Early wheels with captive right side (rear wheels) can be modified for a custom made internal lubrication tool, by grinding the finned inner spacer diameter slightly....so it is removable without removing the left side outer race (but you have to do this once, this time). /5 and /6 wheels are like this, in general. Once you have your wheel apart, all this talk will be vastly clearer.

6. IF you are doing the FULL preload job, you will be cleaning the bearings in something like kerosene or other grease dissolving/cleaning liquid. The FULL preload check is done withOUT seals in place, and the bearings are cleaned of grease, dried somewhat, and are then OILED. Install the bearings in the proper side of the wheel (you did NOT mix them up??), together with all spacers, etc., that you may have removed. The only parts not to be installed are any trim pieces and the grease seals. The early wheels are shown in the books as being serviced by heating the hub and totally removing the entire 'works'. I consider this not a good idea, constantly heating and removal over some years, with the attendant possibility of long-term damage, and recommend the modification of the finned spacer, and use of a special greasing tool (Ed Korn's??).
There is also the special cleaning and greasing tool made by Chuck Walus, in the late 1970's and into the 1980's, described in the addendum area, below.

Mind the variations, the 1978 DRUM and DISC rear, and the 1979 and later, talked about elsewhere's on this site.

NOTE!! The 1978 REAR DRUM snowflake is an odd-ball, this can be identified by being a snowflake, rear, drum, and 5 bolts holding the seal retainer. It has a NON-insert hub, and must be heated for servicing the bearings, and is a POOR DESIGN.

7. At this point I will describe the preload in more detail, how it is basically measured, and the 2 special adapter tools needed for such as a 1983 or 1984 bike, that was used for making this article (we are talking here of the FULL procedure, an ACTUAL measurement....not the FEEL procedure):

Special note!
Wheel innards assemblies that have to be heated for NORMAL service, that is, as delivered by BMW in stock form (non-modified inner finned spacer), must have the preload 'formally' tested or adjusted with the entire pack assembly removed from the wheel. This is not great for the wheel, to be heated and the stack removed so often. That is one reason the inner finned spacer is recommended to be modified, a 3 minute job at home. While spacers and string and pull-scale CAN be used with such a stack, there is more room for accumulation of errors. HENCE, it may well be better to modify that finned spacer, and do this job by feel, or external spacers made up and do it somewhat like is described in this article.

When the proper width spacer is present in the wheel, the wheel mounted normally in the motorcycle, the axle nut tightened, then the force from tightening the axle nut tries to squeeze all the parts in the hub, together. A very tiny amount of 'free play' must exist to allow the wheel to turn without substantial friction and allow the bearings proper running clearance. BMW specifies a certain preload, and this is generally 21-42 inch-ounces. My PERSONAL feeling is that this is rather a bit too much, and I generally use a lower value, or, more accurately, I tend to try to set the preload at the lower end of that specification....see later herein. It is possible to measure the preload, seals removed, with the wheel in the motorcycle, pulling on the tire circumference. This is difficult to do right, so, forget it. On a practical basis, for the FULL, actual MEASURED procedure, the wheel has to be out of the bike. Since the wheel is no longer in the forks or swing arm(s), some means for keeping proper side to side pressure on the bearings, hub parts, etc., must be made up. This is done with spacer tools, often one for each side of the wheel. These spacer/tools can be of different dimensions than what I am specifying herein, and you should determine what you want, after taking a look at your wheels, their outer hub areas, axles, etc. Frankly, 1.5" in diameter is probably best. These two spacer/tools must be made on a lathe, and fairly precisely. This is a very SIMPLE job for any machinist. NOTE that on the old style wheels with no lip for the outer races, the whole internal 'pack' is assembled on the bench, out of the wheel. So, for those, this is a considerable difference in procedure from the later wheels....but the IDEA is the SAME!

NOTE: When I made up these steel spacers for use with my 1983 R100RT, I made them with a central bore of 0.670", tolerance +.002", -0; length 2.125 to 2.250 for one of them and 2.75 to 3.00 for the other. Whilst I used 1.5" stock, 2.0 inch is a nice number, will work against the bearing properly, and the calculations are easy with those too. The spacer should be a very smooth easy sliding fit, NO excessive play, on the cleaned axle.

8. Let's get back to the 1983-1984 Airhead that I used for this article:......the spacer/tools length must be such that they replace the width of the forks, or somewhat anyway, and yet are not so long that when in use you cannot fit the axle and axle nut through the entire wheel assembly. The inside diameter of the spacer/tools must be the same as your axle...PLUS about a thousandth or so. To get a really accurate preload measurement the spacer/tool INSIDE bore must be smooth, and a smooth fit for the axle...but absolutely NOT a push force fit. You want the axle to be easily insertable and removable in the spacer/tool, axle oiled, but not loose enough to allow the axle to cant sideways in the bore, yet not tight enough to grab the axle at all. A nice EASY slip fit. So, you need to supply your machinist with your axle...and that axle should be cleaned with steel wool, etc., before giving it to him. Tell your machinist you want an easy, non-cocking slip-fit, axle oiled. If the spacer the machinist makes for you falls of its own weight onto the axle lightly oiled, and does not cant, that is likely just right. In addition, the end faces of these spacer/tools must be flat and square to the bore. Make them of common steel, not aluminum. The final specification is the outside diameter. This needs a wee bit of thought, for TWO reasons:

a.) The correct diameter means an easy mathematical calculation for preload
b.) The correct diameter is one such that the spacer/tool fits...presses against...the lipped spacer/outer bearing part, yet not so large that the spacer/tool overlaps the bearing and presses on the wheel hub....or so small it does not press on the parts properly. This is very self explanatory when you look at the wheel bearing, hub, lipped spacer. Because all the bearings are the same diameter, I have selected, for the standard snowflake wheels, a spacer/tool diameter of 1.50 inches, and one of mine is 3-1/8" long, and the other is 2-1/4" long...and these are the one's I used for the 1983-1984 wheels in this article.

NOTE!! It is possible to use some old pipe and make adapters. One must be careful in doing and using this method. You want repeatable measurements. I recommend against this, unless the ends are flat from being made on a lathe, and you are VERY careful in their use, to be centered, squarely, ETC.

NOTE: elsewhere's in my wheels articles, you WILL find mention of a 3/4 inch pipe...which is used to enable fitment of the innards assembly....this is NOT the spacer/tool in THIS article!!!

9. In checking the preload with the wheel, hub parts, axle, spacer/tool(s), axle nut, but NOT the wheel seals, remember, this procedure is for the 1983-1984 wheels I used for this article......
.... For earliest wheels, you assemble this whole innards stuff onto the axle, and use a somewhat different method....the wheel hub is not even used on the earliest types, as you have a larger round outer spacer. Once you understand THIS article, you can apply it to earlier wheels with a bit of thinking and looking...and maybe some information from the articles by Gary L. Smith in BMW-MOA magazine; and as delivered in a Seminar at the BMW MOA National Rally in Spokane in 1984....and published elsewhere's as well.

Continuing....

>>>Assemble the oiled bearings into the wheel, and the hub parts, withOUT the seals. Tighten, using the one or two spacer/tool adapters and the axle and axle nut. Tighten to spec. You should be able to rotate the axle assembly SMOOTHLY.

Wind a piece of light string around ONE of the spacer/tools, perhaps a dozen or so turns, in ONE layer (overlap the first few turns so the string stays in place). Attach a spring scale, cheap ones are fine, see Sargent Welch Company, for such as model 8004 spring scale, to the end of the string. Hold the wheel upright, that is, normal position, and pull on the string scale SMOOTHLY and CONSTANTLY. The scale will jerk some, especially as it starts the rotation, but hopefully not excessively. If the scale shows a perhaps 30% jerky variation, or more, you may have poorly made adapter tools or other problem. READ the scale during the smooth part of the pulling as the axle spacer turns. You are not interested in the START reading, but the reading DURING the smooth rotation of the axle assembly in the wheel.

Convert the spring scale reading as required, and change or modify the wedding ring spacer as required, and repeat measurement and modification, until within specifications.

10. Specifications are, by the book, 21-42 inch-ounces. If you see official figures in the various metric numbers, you may see this as 1.5-2.5 CMKp or 15-30 Ncm. Again, I think this range a bit too high, can lead to scorched bearings, so I set my own high limit to 25 inch-ounces, and prefer shooting for a 15-25 inch-ounce setting. NOTE!!! Tapered bearings have an OPTIMUM preload. If the preload is less (more looseness), the life of the bearing DEcreases, but much more slowly a decrease for each relative bit of looseness......than the much faster decrease in bearing life as preload is INcreased from optimum. But, too much looseness means lousy handling. I have found that 15-25 is a nice area. You may well want to use the factory specifications. This is up to you. Certainly if you are using values below the factory 21 inch-ounces, you want to be especially sure of what you are doing. You probably will find, as I do, that 'trying for 25' is a very nice value; and you probably will want to avoid under 25 or over 30, particularly if your bike hauls a trailer or, especially particularly if it hauls a sidecar.

NOTE that, as described well back in this article, many BMW shop mechanics, and others, do not measure the preload, they do it by experienced feel, as they draw up the axle nut. This is not for the first-timer, without an expert showing them the feel. ALSO note that no matter how good that mechanic is, it is hardly as precise as the pull string method. More preciseness means LONGER bearing life.

11. Unless the spacer/tool is exactly 1.00 inches in diameter (a poor value due to how the spacer/tool fits the bearing size, etc), you must now convert the spacer/tool diameter (in the case specified, that 1.5 inch diameter) to the equivalent, mathematically. So, you need a multiplying factor. This is rather easy!

The inch-ounce specification divided by the RADIUS (that is half the diameter, folks!) of the spacer/tool is the factor.

Since you are likely using the 1.50" diameter tool I suggested, you won't have to do ANY calculating, because I am going to give you the spring scale readings specification! And, in case you were about to say something....you can forget about the string diameter, just do not use rope...use light cotton or nylon packaging twine or inner parachute cord twine.

For your reference purposes (??), 16 ounces is 454 grams and 1 ounce is 28 grams.

In my shop I have pull scales graduated in grams. For the 1.50 inch diameter spacer/tools, the pull force I prefer is 567-943 grams (for the original factory specification of 21-42 inch-ounces, the force would be 794-1588 grams). Convert to ounces if you have ounce scales. The Ohaus #8004 scale reads in the values you need. Cheap too.

12. WIDENING the wedding band spacer will DEcrease the pull force, as the bearings are now held farther separated from the outer races. Change wedding bands, or modify them on a surface plate as noted previously, and use your micrometer to follow the work as it proceeds.

13. Once things are within the specifications you desire, you must remove the bearings, de-oil them, dry them a bit, clean up the outer races, grease the bearings and install them, and install the new seals (containing the lipped spacers). Set the spacer/tool in the box you keep your wheel bearing grease and other such items for the wheels. Good idea to do the feel test AS you slowly take up the axle nut::::...just in case you goofed!

You will find that doing the preload checking takes very little extra time during a tire change. I suggest that you do the tire balancing at the same time......when the seals and lipped spacers are OUT, and the bearings OILED.

Addendum #1, 10-03-2002: The 9.2 mm short lipped spacer used at the wheels is also about the same as used at the swing arms. It seems to actually measure 0.357" wide, it is part number 36-31-4-038-142. The 10.7 mm lipped spacer that is used with 120 section rear tires, on the right side of the rear wheel, is 36-31-2-301-737. These spacers vary from the 9.2 and 10.7 and the inside bore, lip, etc., a very tiny amount, seen only on a micrometer.

Addendum #1, 06-21-2004: There are some other anomalies in the wheels, such as earliest /5 having a smaller right side bore for use with a smaller seal. The procedures, above, were from actually working on an early 80's front and rear wheel, and should not be taken as absolutely correct for all years and models. There is a special greasing tool that was made and sold by Chuck Walus back in the late 70's and into the 80's, that is very handy for greasing bearings in your hand....and for flushing and/or greasing bearings even on the captive right side ones. It was described in the June 1978 BMW Owner News, on pages 23 and 24.

PART 4: From 1985

As was mentioned near the beginning of this article, BMW, in 1985, changed design of the bearing and associated parts, in the wheels. Whilst I have not personally seen this particular anomaly....it supposedly exists: The R65LS was produced between January 1981 and October 1985. The FRONT wheel of that model, per the BMW information CD, ETC., uses a BALL bearing, part 36-31-1-242-854, which is the same size as the taper bearings: 17 x 40 x 12.... a type 6203. All the other models changed, at not the same time, to 6005 bearings which are 25 x 47 x 12 mm. Supposedly the changeover for these occurred at:
R80, R80RT in 1985; R65 in 1986; all the rest in 1987; note that this hardly applies to the REAR wheel on single-sided rear suspensions, such as the GS and R models, as they are totally different internally, with the wheel bearings being inside the rear drive, and only 0.50 mm (0.020") play, as measured at the rim, is allowed.

For all the models with the ball bearings, the bearings are to be replaced when noticeable free play exists. These bearings are lubricant-sealed for life. Life may be long, but not as long as a properly taken care of tapered bearing type of the earlier models. I think about 40,000 miles is about it for them. One reference book says that the 1985+ ball bearings are replaced by heating the wheel hub to close to sizzle temperature and using an internal expanding puller to remove the bearing, and then, while the wheel is still quite hot, tap in the new bearing to flush depth. Another describes, more accurately, that late bearings are COLD PRESSED. One can use any proper diameter socket for the tool to drive in the new bearing....be sure that socket bears ONLY on the bearing outer portion. The front wheel ball bearing on the late models is the same as the bearing used on the Y spoke K models and the K11 series left bearing. The bearing is 36-31-1-450-859, and is a 25 x 47 x 12 mm ball bearing, and the FAG number is 6005. That BMW number was superceded, and may be yet again, BMW tends to do that.
The superceded number is 36-31-1-469-265. Nothing wrong with any common 6005 bearing, and FYI, the grade is C-3, and it is a sealed bearing; and you might see on the bearing something like this: SKF 6005-2RSH/C3.

Revisions:
05/10/2003: add link for Duane's site
09/15/2003: some clarifications, and add PART 4:
02/26/2004: editing and adding references; simplification notes, etc.
05/23/2004: Re-edited slightly
05/23/2004: Updated considerably
05/24/2004: Edit information on R65LS front bearing information
11/23/2004: clarify using magnet to detect cast-in steel insert; very minor other things.
06/04/2005: some update and clarifications
07/26/2005: Expand information on the later ball bearing models
03/01/2006: Add more Kukko information, and reference to Ed Korn
02/23/2007: minor editing
05/04/2007: Clarifications, and add Ohaus #8004 part number at several places
10/1/2007: add, in last paragraph, the superceded number and the grade+.

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