I previously published an extensive article on the EARLY AIRHEAD FORKS INTERNALS. That article, with photos and sketches, described the /5 through /7 forks internals, including modifications for sport-handling and race-handling. The article is no longer in my files, and was published on the Airheads LIST before I started this website. If you can find it in the archives, please refer to that article for those early forks. I may get around to doing the article all over again, as I still have many of the pencil note references I used when I made the original. Now and then I may find notes that led to those articles. I will put such in an ADDENDUM at the end of this long forks article.
I never did the same thing for the 1981-1984 forks, which are different internally. In this FIRST section of the following relatively lengthy article, is a .jpg of a sketch, and description, of how these 1981-1984 forks operate, some information about the modifications the FACTORY did during production to REDUCE NOISES and IMPROVE OPERATION, etc. There were THREE stages of these changes. While the factory never identified these as stages, I, as others have, identify them as Mk1, Mk2, and the final as Mk3. AFTER 1984, many of the forks used MUCH of the Mk3 design. The below photo of a sketch is of the 1981 fork, but with the last version of the factory modifications, which I call Mk3.
The 1981 forks were of a very different design. They also made a lot of clicking and clunking noises. BMW's first fix was to install SHIMS below the valve body, which did reduce noises. The rebound spring above the damper valve rattled, but relatively quietly. This change lasted into 1982.
The new valve had a shortened length body and a special tabbed (on upper face) spring washer was used to push...well, force...the valve body against the top recess of the original orifice plate. This change was probably done primarily to eliminate hand-shimming in production. Another modification was to eliminate the original steel washer that controlled the oil flow. Instead a thick Teflon ring was used, which fit tighter and was quieter. The upper face of the valve body was machined to fit the thicker ring, and movement was thereby restricted, between bump and rebound, giving MORE bump damping too.
The final change, shown in the sketch to the left, which I call the Mk.3, came in 1983. The valve mechanism was SHORTENED, and the bottom had a recess containing a spring, same as the rebound spring. This prevented any oscillation. It also improved the fork operation during AGGRESSIVE transitions between bump and rebound conditions. The springs also improve the operation of the hydraulic 'stop'.
NOTE: Because of how these forks are designed, it is very important that the oil have a very good anti-foaming characteristic.
The over-all damping is dependent upon oil viscosity. Certain characteristics of fork operation are dependent on fork oil level (or, call that fork oil amount). BMW lowered fork oil levels, republishing the specifications. Those who modify the forks for one or another purpose know about these things, and more.
I will BRIEFLY describe how these forks work:
When you hit a bump in the road, the 'slider' (fork lowers) go upwards, and oil moves from the lower area inside the fork, through the gap between the piston rod and the valve body. The valve ring pushes against the orifice plate, and oil moves to the upper chamber area by means of the gap under the ring. The gap itself IS THE RESTRICTION.
On REBOUND, the piston descends, and oil is forced against the ring, sealing it to the valve body. The oil path is the small orifice at the upper end of the piston rod, which passes oil MORE SLOWLY than the gap below the ring, thus providing stiffer rebound damping. As the slider descends, the lower chamber becomes larger in volume, and oil comes from inside the piston rod, via the orifice at the LOWER end of the rod.
The gap below the valve ring and the upper piston rod orifice determine the relationship of bump and rebound damping(s).
A superb article on motorcycle front fork alignment
That article was done by Randy Glass. Lots of images. Highly recommended! This is the GOLD STANDARD for basic motorcycle fork alignment.
***Periodically I check this, but, STILL, as of September 26, 2014, the above link will NOT work properly in the various browsers I have checked it on. The problem is, I think, that the article was written using a very old version of Microsoft FrontPage and Arachnophobia. Duane was informed years ago about this. I suggest that you
try the following link,
which avoids you trying to play with code and settings to TRY to get it to work:
You may be intimidated by that article. It IS comprehensive and detailed; but....it is not a difficult job. Randy's article, which was written as he worked on his BMW Airhead quite some time ago is/was so good that I never wrote one like it myself, I just refer folks to it. I admit to minor contributions to that article. The photos really tell you what you need to know if you wanted to get into it in depth. But, whether you do a complete job like Randy spells out, or not... it is good to know what the proper and best procedures might be. Most will not have forks that are in dire need of the full alignment...but most would be improved considerably. Reading the article will let you know what CAN be done and HOW it is done. You will see as you read the article that some much simpler checks may well be all that you need.
You will also see by example and photos what
the very important reverse-torque method is, to avoid twisting your fork
tubes. The illustrations of the anti-torque method
are just ONE type. I have some photos that are NOT in that
article, regarding torque and anti-torque tools, and they are
later in the article, below, that you are presently reading.
In MY article that follows, you will get enough information to do adequate alignment, and then some, for most situations.
This article applies to most motorcycles with older-style
conventional telescopic forks. It is especially so with the
smaller tubes and triple clamps that are not very thick and beefy. The
smaller the thickness, the easier it is to
twist or warp them. Many top triples are steel plates
that sit on top of the tubes. Some
other types are clamping types, some have
machined recesses, etc. Some are of sturdy aluminum or
magnesium alloy castings. The more mechanically beefy
and/or clamping types with recesses are less
likely to allow the tubes to twist or otherwise go out of correct
Many a motorcyclist has ridden with a front fork that has a steel or aluminum flat plate as the top triple clamp, and is quite surprised at the improvement in handling from installing an aftermarket top triple that grips the tubes and is precisely and ruggedly made. Due to the forces from the wheel, at the end of a long lever (that lever is the long tubes, etc.), the forces at the top triple can potentially be rather large, right on up past the lower triple clamp (which is often very much beefier than the top triple clamp). Few folks install a beefed-up lower triple clamp, as usually the lower stock one is quite sturdy and is positioned much lower on the 'leverage'. Some of us old-timers remember obtaining an extra lower triple clamp and using that lower triple clamp, modified, as a top triple clamp. Can be a bit ugly, but quite effective. Our biggest problem, and reason we used the lower triple clamp for the top, was that machining from a block of aluminum to the accuracy needed was a huge chore back then.
Aftermarket beefy top triple clamps are available for many motorcycles, but some are poorly machined and can make things worse. Some are wonderfully made!! Some require a bit of ingenuity and work to make them fit properly....such things as headlight mounting ears, or? may require modifications, etc. Today's numerically-controlled milling machines can make these items easily and quickly, ONCE SOMEONE DOES THE PROGRAMMING AND SETUP.
MOST folks are surprised at how handling improves with a stiffer top triple clamp as opposed to a stock flat plate. This is not so on all bikes; some come with beefy top triples.
Adding an aftermarket fender brace is often NOT all that effective...and if not hand-fitted to avoid stiction effects, can make things MUCH WORSE. In general a stiff top triple does a LOT MORE for handling.
The motorcycle manufacturer may well have installed a
somewhat less stiff top triple clamp ON PURPOSE, to give a
certain FEEL, which is part of the over-all chassis design.
But, for crisp & tauter handling, a stiff top triple clamp is
almost always quite helpful. I know of no instances that it
does not give better handling and feel on an Airhead that
originally came with a flat steel top triple plate.
NOTE: For information on replacing the steering head LOCK,
Cautions and Warnings:
Early fork interiors contain what BMW calls
"wiper rings". These are quite small piston
rings. I HIGHLY RECOMMEND that you do NOT break
them and do not replace
them unless broken accidentaly. New rings from BMW are NOT properly made, do
NOT fit correctly, give too much friction, and OLD
ones generally will work BETTER than new ones, since they slide
easier. Any minor extra bypassing oil leakage due to rings wear is usually
MINIMAL! These rings are very brittle, so be careful!
The early eighties front forks are quite different internally from the earlier forks. When disassembling the early eighties forks, one of the first things you will do is drain the oil and try to remove the bottom parts. Do not try to remove the metal plate.
For longest steering head bearing life you must not only clean and re-grease them now and then, but it is a GOOD idea to move the steering from full left to full right, to help redistribute the grease....I sometimes do that sometimes when I park the bike.
It is advisable to read this article completely through before beginning any work on the front end.
The exact procedures vary with the bike model and year....different fitments at the top triple are the primary external differences.
In the February 2003 issue of AIRMAIL,
'Oak' Okleshen, in an article entitled "Tank Slappers (from the Airlist)",
succinctly identifies and discusses weaving and the high speed diverging wobble
called a tank slapper. He also states his method of adjusting the steering
There is an IN-DEPTH article on this website with detailed information on steering wobbles, etc: instability
This section has been moved to section 54-10B
It is extremely common for riders to not understand fork
adjustments. For example, the front fork needs to have proper
SAG adjustment. BMW did that at the factory, as an
approximation; by what springs it installed. From 1981,
BMW began using spring spacers to compensate for sag on some
models, rather than spring changes.
You MUST have the front suspension in a reasonable sag operating
range when you are seated on the bike and the bike has its
most normally used loading (you, luggage, passenger if
Have the bike on the center-stand. The front wheel (tire) must NOT contact the ground. If it does, put a piece of plywood under the center-stand. Either do the following by measurements taken by a friend; or make up a zip tie arrangement on a fork tube to measure the change, or figure your own method. Measure from someplace on the fork lowers, to the upper area, with the tire not on the ground. That is the full-extended value. I use the bottom edge of the lowers myself, up to the bottom of the lower triple clamp.
Take the bike off the center-stand; and put a normal load on the bike (you, passenger, luggage, etc.). The forks must compress about 1 to 2 inches. That is a reasonable value, selected out of my hat of experience. If NOT within that range, and you are not going to change springs, remove ONE top cap (top of the upper triple clamp) at a time. Adjust the spacer you may find there. On some models, BMW has inserted a spacer at the top, that sits on the spring...or, up against the 36 mm top slug threaded part. ADD, or change the spacer. On those models with a spacer/adapter that fits in the center of the spring with a nose on it, leave that spacer/adapter intact. ADD a spacer if required. BMW has a spacer, about 5/8", that is 31-42-2-000-399. But, you can make the spacer you need, easily. For the early forks, you can make the spacer you need from 3/4" standard PVC (plastic) pipe, from your nearest plumbing or hardware store. I make mine on a lathe, so it looks nice and has squared ends...but you can make one with a hacksaw, and maybe file the ends nicely square and clean. Install the spacer, then do the other side.
You want to use a spacer that gives you 1 to 2 inches of sag. I prefer close to 2".
NOTE!....the rear shocks come with adjustable spring perches.
That adjustment is not to stiffen the shock, but to level the
bike....but, in effect, what you are doing is to set the rear
SAG. It is a crude way of compensating for
loading, where a different spring would be the better choice,
if needed. About 20% of rear shock travel is
plenty enough. Most will do nothing more than adjust the
shock perch stiffer for use with a passenger. Some
rear shocks have adjustable bound or rebound, however.
Follow the manufacturer's information on them.
Sidecarists: The same adjustments apply for front and rear....unless you have a leading link front end....then, there is a lot more to know....and I do NOT get into sidecars in THIS article.
Inquiries about installing gators on Airheads that came with (OR
them, such as on a RT) are rather common. Gators DO protect the chrome fork tubes
from the little nicks they would otherwise get from oncoming
small rocks, gravel, etc. Those nicks need to be dressed out
now and then, or they will ruin your fork lowers top seals. Some want to install gators and can't find them. 11 and 13 rib gators are
available aftermarket. Rancho Shocks (shocks for cars and trucks) makes various
colored gators than can sometimes be adapted. The original
stock gators, on those BMW airheads that came with them, used a roll pin as a air bleed hole (breather). A roll pin is a
tiny hardened steel tube, with a small gap up the side, so they have a tiny bit of springy capability
if you want to put them in a hole that is very slightly smaller than the roll
The /5 Airhead had 13 ribbed gators, fitting well down the fork leg.
The /6 bikes had shorter 11 rib gators, and were set less far down. With
some fork braces you
probably will want the 11 rib gator. You will need some
sort of air bleed....see next paragraph.
If you have an RT, you CAN use the gators from such as a R80GS. The 11 rib gators can be used. You CAN keep the fairing rubber bellows; or, you can modify the fairing rubber bellows. Unless the fairing rubber bellows are removed or modified, there will be limited fork travel, side to side. If the bike did not come with gators, you may need to install the roll pins (vent pins) 07-11-9-941-470, into the lower triple ...look underneath......there are vertical holes there for that purpose. You need to install them so there is some portion sticking downward...same as the thickness of the -669 ring. The roll pins position the -669 ring, and then the clamps won't crush things.
The parts are:
4 each #07-12-9-952-121 clamps (use these or get stainless steel ones)
2 each #31-42-1-241-669 rings
2 each #31-42-1-241-666 boots
2 each #07-11-9-941-470 roll pins
Airheads AND K-bikes:
If you want to install fork gators, and want INexpensive but entirely adequate gators, you can look at the following website:
You can also just enter the following part numbers into Google. You may have to enter the number with or without the "RS":
Rancho Shocks, black #RS1952. Quite a few other colors are available, pink, green, etc.
Blue is RS1950; Yellow is RS1951; Red is RS1927; Black is RS1952. Available from a wide variety of autoparts places, including NAPA.
My beliefs about fork braces may not coincide with other folks
Everything below is what I think, and do. YMMV!
Note that some of the factory braces are OK, and the hoop braces of CC Products were OK, and can be superior to the Telefix. Be sure tubular braces are bent or otherwise played such as with washers... to eliminate stiction/binding of the forks! The Telefix type will work however, and is used in conjunction with the stock fender mount which is a brace, more....or less.....depending on the model.
ANY form of fender or fork lowers bracing MUST be checked for smooth operation of the lowers....and I will get into that here:
A sturdy upper triple plate does more for handling than a fork brace, in general. If the lowers are badly worn, the brace may help considerably. Some bikes came with stiff cast top triple plates, such as the R65, etc. Others have a steel plate, that is not as good, IMO. You may have noticed that some Airheads have some nice top triple modifications, courtesy of one of our Club Members who designed and had them machined. CC used to sell several types of top triple clamps, fork braces, etc.; and Luftmeister sold some types as well. I caution on the use of them, some I've seen don't seem precisely made.
A fork can be aligned with parallels and a dial indicator, although a piece of plate glass does amazingly well, and that is with the wheel/axle/fork brace NOT in place. The Randy Glass article I cited at the top of this page is a good primer.
Even when the larger procedure of doing all this is not done, what I do is as follows:
FIRST!...HAVE NO SPRINGS INSTALLED AND NO
Install the oiled axle ONLY, loosely into and across the lowers, and with NO springs in the forks. Lift the axle upwards, and see how smoothly it operates (I may well put a dial indicator on the tubes when doing it but not always). There should be no appreciable change during the lifting over just about the full range. The fork/fender brace is then installed. They can really upset the alignment, so shimming, hand re-work, bending, whatever, depending on the type, is sometimes needed. Once installed properly, there should AGAIN be no change as the axle/lowers (still no spring, no wheel), is lifted up and down.
At that point I install the wheel, LIGHTLY grease the axle and install it and then tighten the axle nut, and equalize the lowers on the axle, and THEN tighten the pinch bolts. The front end should now still be very smooth. Then I reinstall the springs and caps. I might check the sag at this point too.
A properly installed fork brace will mask problems with worn fork lowers, and in that respect will help. For most fork braces, properly installed, there is a stiffening effect, noticeable in some types of riding, particularly bumpy cornering and some other situations, that helps, not overly-greatly. A massively and carefully built fork brace, properly installed, can make a difference. Generally, the heavy dual-hoop tubular ones are much better. Any that are not made very well, or distort the forks upon installation, will make the handling WORSE! A better top triple clamp, in many instances, does far more for handling. Both a stiff top triple.....and....a good and properly installed fork brace....are, together, a good thing.
"Stiction" is used to describe a property of two surfaces that are sliding with each other. Stiction, the word, is used by motorcyclists almost exclusively to describe front fork stiffness before movement. Stiction is typically NOT described by some VALUE, but by the perception that the initial force it takes to START the sliding is much higher than the force to CONTINUE the sliding. If stiction is high, your forks will not follow small road irregularities very well, and handling will be poor, and I have seen plenty that were awful. Stiction will greatly affect the comfort and handling over small road irregularities, including tar snakes and bigger. Stiction does not have to be very high before handling on even VERY lightly bumpy roads becomes truly unpleasant. A fork with light to moderate stiction will not respond properly to tar snakes and other road irregularities, and will ruin the good handling the bike had designed into it. It is particularly annoying on irregular paved surfaces in moderately sweeping to tighter turns, because in the transitioning, the forces are somewhat sideways, and telescopic forks are lousy at handling side-forces....and stiction can get MUCH worse in turns.
folks try to compensate for the combined effects of stiff
springs, stiction, and other things, and often increase the oil
amount in the forks, (or more often they increase the oil
viscosity). In general, these things cause the
handling to get REALLY BAD! I suggest that you use the
proper oil and amount, at least initially, after you reduce as
much stiction as possible. Stiction will REALLY make
Here is a relatively easy test for
Remove the front wheel. You may have to remove the brake calipers on disc-braked bikes (and do NOT hang them by their hoses!!). Unfasten the top tube nuts or whatever they are, and remove the springs. You may have to remove the handlebars on some models. YES, the central nut on the top is still there and tight. The top is complete, together, just no springs. Reinsert the axle, oiled, but don't tighten it ...that means no clamping, no axle nut tightening. If the axle does not fit VERY smoothly, clean it so the axle fits easily and smoothly. That is a MUST! You might have to wedge the slot at the fork lowers very SLIGHTLY more open. If the axle is rusty, has nicks, or the lowers have a problem, clean up the metal.
one hand on each lower fork assembly, and slightly move the
lowers towards each other, and away from each other. With a
nice slippery axle you should see some movement...you should NOT need much force and do
NOT want to use much force. Find the approximate
center of the movement, and leave the lowers at that point. LIFT at the
axle....so the lowers, with axle inserted....moves upward. Take it pretty
close to the maximum upwards movement. If the stiction is high, you have a
problem to investigate. The first thing to try is to unfasten any braces
(that includes the fender mounting which acts as a brace), and
retry this procedure. If the stiction mostly disappears, you must
deal with the braces by bending or washers/shims, whatever is appropriate to YOUR
bike. If the stiction does not disappear, you need to get a
pane of glass and maybe a dial indicator, and find out just how and how much
the tubes are twisted. Once you fix the alignment of the tubes in the triple
clamps; you can again check the above method; and then if OK, add a
brace or the fender mount;....and as noted we may have to bend or shim braces.
It is very important to understand that at every step in the procedures I outline here in this long article, you are advised to continue checking stiction, as you do your work. What I mean by this is that if you do an initial check with the springs out; then, when you have the springs in and the spring caps back on (as, let us say, the next step), REcheck the stiction.
>>>There HAVE been rare instances of a bent top
triple plate, or other hard-to see anomaly, so if stiction starts up when you
do some particular step in the procedures, then find out why and fix it!
Aftermarket braces have been the cause for lots of stiction. SOME aftermarket braces can NOT be adjusted in the plane you would like to.
Even if the tubes and triples and braces, etc., are all assembled correctly, you can add stiction by not equalizing the lowers on the axle before you tighten the axle nut (some models) and/or fork lowers axle clamps.
FINALLY, one last word on stiction: If you install new BMW wiper rings inside the fork, you may have problems...they do not fit properly, have high friction too. Use the old ones! If you broke the originals, make sure the ones you install have a decent amount of ring gap.
The steering head bearing is common type 32028, 28 x 52 x 16 mm.
BMW has used this number on all the Airheads, and even the
BMW dealerships have all sorts of prices for that bearing. There are variations on the 32028 part number, you may find 320/28X and other things.
The bearing may be listed as I.D. 1.102"; O.D. 2.047"; Width as 16 mm. You can purchase this bearing almost anyplace, even a local autoparts store, which MIGHT list it as a A-32 bearing. Just ask for a tapered roller bearing, and provide these numbers. Prices will be MUCH cheaper than many BMW dealerships ask.
Swing arm bearings are 30203A, 17 x 40 x 12 mm; and are basically the same as MOST of the pre-1985 wheel bearings, which are 30203. The difference is sealed versus unsealed. Frankly, I like them UNsealed, at both places. Every few years I remove the entire rear end, and hand clean those bearings. If I am working on a bike and find sealed ones, I puncture the seal, or otherwise remove or disable it, so I can get proper greasing in the future from and into the 6 mm Allen adjuster hole.
My comments for the steering head bearings pricing and where to buy, above, APPLY for the most part to the swing arm bearings and wheel bearings too.
The bearing puller, Kukko or similar, works very
nicely. A Kukko is not cheap, and a few adapters are needed for shop use.
Due to the cost, many use other methods, depending on what they might have
or have access to. The use of an electric welder to create a hot spot
or a bit more around the lower steering neck inner race, and thereby enable
cracking/shrinking it, works OK, it just falls out. For the top race, a
similar use of a welder works fine too, and you can weld something to it, to
lift the bearing out....a couple of 'fender washers' perhaps. The use
of a Dremel, or other high speed tool with an abrasive disc to cut nearly
through the outer race, then a tap with a hammer and chisel, also works OK,
but takes a fair amount of time...and discs.
Additional information on seal pullers and bearing pullers, including much cheaper ones, are item 22 in this article: TOOLS
The reason these various things are done is because the bearing outer race fits in a shelf, and you cannot use a long drift tool from the other end of the steering stem to knock out the bearing outer race.
The steering stem tube itself is fitted into the lower triple clamp, and MY advice is that it should NOT BE REMOVED. If you do, you MUST heat the triple, and you will need to INDEX the stem during replacement (heated triple again), otherwise you will not have the lock slot in the correct position. If you press or bang the stem out withOUT heating, you could RUIN the fitment; and you COULD end up with constantly, forever, changing steering adjustment. The factory manuals will show that the lower triple clamp, may be it will be called a lower fork bridge, is heated to sizzle temperature (100°C or 212°F), and then you drive (soft hammer or piece of wood and hammer) the tube downwards, then reinsert the tube without the bearing, then heat the bearing and install. Please avoid trouble...and do it MY way:
There are several methods I approve of, that will keep you out of trouble. One is to use a Dremel or similar rotary tool, and cut the bearing and then use a hammer and chisel on the cut. Another method is to heat the triple, moving the steering stem just enough to, after cooling, get two screwdrivers between the bearing and triple, then you can pry up the bearing off the stem. You can then RE-heat and reset the stem depth. NOTE that this will usually ruin the lower dust cap, so order a LOWER dust cap ahead of time. You don't absolutely have to have a dust cap, of course, but I recommend you do. There is a third method, you can purchase aftermarket tools specifically designed to service the steering head bearings. Ask on the airheads list for the latest vendor information.
When installing the new outer races, I do it with the old outer race, or, a steel part I made in my lathe for the purpose, or, I may just use an appropriate size of socket. Use of a large size long piece of All-Thread from the hardware store, and large heavy washers or sockets and washers, etc, will also do the job just fine. Be VERY sure that the outer races area of the steering stem are dead clean of any foreign matter...right into the edge where the bearing fits. Be VERY sure that the outer races are seated 100.0% fully...otherwise you will be adjusting them over and over, as road pounding, etc., cause them to seat further inwards and your steering loosens. Not a good idea, especially at high speeds, if too loose.
Use a NON-moly grease on the steering bearings.
Recheck the adjustment after some miles. If you installed the outer races properly, and did not mess up the stem fitment, the adjustment will be stable.
Plan on cleaning and regreasing every few years
(just lower the steering an inch or so).
NOTE: Occasionally someone asks something like this: "When removing the outer races of the steering head bearings with the 'welding procedure' is it sufficient to just to
disconnect/remove the battery to protect the electronic/electric circuits or are there other protective steps required?
This is my reply:
Yes, disconnect one side of the battery. But....AFAIK there have been no reported incidents of problems with any Airhead of any year. However, in the instances (every one of these was at a TechDay) where I have used a stick welder to enable cracking of the outer races, I make sure all aftermarket electronics devices are disconnected. I unplug the turn-signal flasher relay (later ones have electronics), disconnect the plug from the instrument pod (except /5), and I remove the front cover on the electronic ignition models and disconnect the three pin plug to the canister...then I use aluminum foil or other means to short-circuit the three pins together (canister side). I disconnect the ignition module plug. It is quite likely not necessary to do all these things, but I have done them anyway, as extra insurance against problems. BTW, I ground the welder at the opposite outer race.
Cleaning and re-greasing steering head bearings:
Cleaning and re-greasing the steering head bearings may eliminate "notchiness" that seems
to indicate the need for new bearings and races. It is likely best to do this procedure soon after installing new,
balanced tires, as
road crown, squaring wear, and balance, will have an adverse effect on trying to make final on-the-road
adjustments. Shops do not clean and re-grease steering head
bearings, they simply replace them. The reason is labor costs, if the cleaning
and re-greasing then shows the bearing to still be poor in feel. YOU don't
have that labor cost limitation, right?
In a SHOP situation, labor is THE expense for the customer, and having to clean, assemble, adjust, and then find out that the bearings are still notchy...can be a waste of time &, thereby, customer money. In a home situation, with you doing the work, it is only another hour (two at the most, including doughnuts and coffee breaks) to try cleaning, inspection, relubrication, partial re-assembly and preliminary adjustment. If you then find the steering notchy, you do not have all that much work added to then just remove the front end, because you have only retightened the top adjustment nut for a check...no need to install nor tighten the top acorn nut, assemble the bars/cables, etc.
If you remove the top area, and the inner bearing, and look at the cleaned outer race, and see vertical marks: if you can feel them with a fingernail, REPLACE THE BEARINGS.
Cleaning and lubrication of the steering head neck bearings is not a difficult job, but if a bearing is found truly bad, replacing the bearings and outer races is more labor intensive, as one must deal with fairings, brake components, cables, removal of the entire front end, how to remove the bearings, etc.
Contrary to some popular belief, our BMW steering head bearings of the tapered 'Timken' style may well last over 200,000 miles. If the bearings and their races are in good condition and properly greased and adjusted, the steering will be light, smooth, without notches. Notches almost always are in the straight ahead position. Greasing is critical for not only hardened grease problems, but for protecting the bearings from moisture, which ruins them. The upper and lower dust cups help to protect the bearings. You likely will not find out if the bearings are bad until you first try the cleaning and greasing and simplified adjustment. The differences between airheads is mostly minor, with improvements after the /5 models in the parts used to adjust the bearings; and, later, changes in the top of the top triple fitments. Cleaning and re-lubrication is recommended every 30,000 miles, especially with the open non-faired models, and particularly if driven often in the rain. Depending on grease, time, and mileage, cleaning and re-greasings may be 5 or 10 years apart, in good conditions.
Do not use greases containing moly (molybdenum disulfide) compounds. My experience with moly is that it does not work properly in this application. Almost any light grease will be OK. It is desirable to use a grease with good smearability, good water resistance, and particularly a low evaporation/hardening over time. I use Chevron NLG1 or NLG2 Ultra Duty EP, a red colored grease, available from a Chevron Distributor, and not your local gas station. Typically they want you to purchase a small box of these grease gun tubes. This grease can be mixed with about 30% moly (or Staburags or Optimol) and used for clutch and rear end splines...but don't use that mixture at the steering head or other tapered type roller bearings; nor, for ball bearings. The plain unmodified grease is also very good for automotive chassis and U-joints. BMW red grease is OK. Generally speaking any thin non-fibrous grease will work.
EARLY Airheads, such as unconverted stock /5
bikes, used a somewhat different adjusting method for the adjustment ring just
under the top triple clamp. Many have converted them to the later
non-split ring type. The adjustment on the earlier type is done with
a small diameter rod that is part of the tool kit, and is a slight bit of a PIA,
Adjusting the 1991+ (and
some earlier) steering head bearings....this applies to the
R100GS, R100R, and the K75, K100, K1100 bikes:
I have not written up a separate procedure for those bikes.
Enough information is available at:
The only major difference is the use of a sleeve tool; which, when properly utilized, will eliminate the need for road tests (one hopes). MIGHT minor adjustments to find out if the initial adjustment was too loose or too tight, especially if a sidecar is being used. Note that in these later forks, there are two types, one uses the sleeve tool. Anton Largiader's website discusses this adequately.
>>In our society of sue-crazy individuals, the following disclaimer applies: I take no responsibility for the following procedure, nor for any ineptness on your part, such as failure to tighten things!...etc. Airhead Canon #8 (and others) applies!
I originally developed and wrote this procedure using both a 1983 R100RT and a 1984 R100RT...YOUR bike may be somewhat different, but the basics still apply.
1. Remove the gas tank. Avoid scratching the paint, especially watch
for interference with the opened
seat: the left front edge of the metal seat pan is not nice to your tank paint. If there is a problem with
interference, remove the seat. With the tank removed, now is a great time to inspect wiring, nuts and
bolts, perhaps even the starter motor, breather, whatever. I usually recommend you service the
electrical system contacts, plugs, sockets, ETC....even cleaning the ignition coil(s) at this same time
you have the tank off. Heck, service those fuel taps (petcocks). If you have a damper knob, remove
damper knob center screw, remove knob, spring, plastic spacer.
2. If you have the BMW hydraulic steering damper,
you will need to disconnect the forward, large end,
at the fork adjustment area ball. If you have a BMW fairing, you must first remove the small
rectangular rubber plug at the fairing, you will re-glue it into place when all done. Then rotate and
remove the damper wire clip (the wire clip, if you are not familiar with it, is the same as used on the
shift linkage of many models). To remove the wire clip you must rotate it off the shaft where it is
clipped to, then it will pull out of a tiny hole in the damper ball socket. Do NOT loose that wire clip.
Pay attention as to where and how it fits. DO NOT try to force the ball and socket apart if you have
not removed the wire clip, you WILL break the ball socket. Once the wire clip is removed, the
damper forward ball socket will pull down off the ball. It might be somewhat frozen to the ball, you
might then have to force it off with such as a screwdriver blade. Push the damper backwards, so it
collapses. When reassembling this area, you should clean and lubricate the various damper parts,
including oiling or moly greasing the ball.
3. Remove the dress cover at the handlebars if you
have one. Remove the instrument pod assembly if
you have one, by first unscrewing the speedometer cable 'nut' at the cable/pod and then remove the
cable. Loosen only the 3 each 10 mm headed bolts holding the pod to its bracket. You do NOT
have to remove those three bolts. While you are in this area, note if you have WHITE colored
rubber vibration isolators. If so, replace with the updated, probably BLACK ones, from your dealer,
they will reduce instrument vibration and prolong instrument life. Now lift up and remove the
instrument pod from the bracket and remove the phillips type screw at the center of the pod's
electrical connector & wiggle out the cable/connector. Set the pod aside where you won't trip over
it. When reinstalling this cable, spray a small amount of contact cleaner-lubricant or silicone spray
into the contacts. If corrosion is noted, remove the corrosion, as best and as neatest and carefully
as you can, before using cleaner or spray.
4. Using a substantial sized hammer if you have to, and the BMW tool
flat spanner (you CAN
hit that wrench with a large hammer on its sides), and being careful not to damage the ignition
module if you have one, loosen completely the 36mm top stem CAPnut. This is a bit different on
the later models. Do NOT loosen the lower triple clamp clamping bolts at this time!
You want to avoid twisting the forks. Below is a photo showing ONE method of using an anti-torque
tool; for TIGHTENING mode. This same idea, photo courtesy and permission to use here, from
Randy Glass ..see article noted above in http://w6rec.com/duane/bmw/fork/title.html is used
for loosening and tightening the fork top caps, and that includes the loosening and tightening of the
center nut, an early style center acorn nut is seen in this photo, with damper rod coming up through
it. NOTE that there are other methods, and one is to use a pry bar or huge screwdriver, between
the handlebar mounts (assuming they are still in place on the top triple clamp). In this photo, a pin,
you could use a bolt, is placed in one of the top triple clamp holes, and the right hand is tightening
the right side fork cap; & the left hand is putting counter-torque on the fork, using the pin & acorn nut
as pry points, the left hand pressuring in counter-clockwise direction. This procedure is hardly
known by anyone but professional Wrenches'. By positioning your pin/bolt, & the pry bar (here a
very strong screwdriver), in the proper hole and position, you can tighten or loosen either left or right
fork tube top nuts, or the center acorn nut, without worrying about twisting the fork tubes in
relationship to each other, which CAN?DOES happen, and ESPECIALLY if the fork is against its left
or right mechanical stop. Randy's article, on Duane's website, above, really should be reviewed by
you, it is a world of GOOD information. If the fork acorn nut and or top caps are quite tight
(usually are, and tight is proper), you may want a friend to help you use the anti-torque bar or tool in
loosening and tightening these items.
In the photo below, the screwdriver tip seems to be pressuring the large closed end wrench (also called the BMW DogBone wrench) on the right side, this is not so. The photo shows the wrench and screwdriver for the TIGHTENING direction, but simply move the screwdriver shank to to the other side of the upper pin (or shoulder bolt, or whatever you use) and the other side of the crown nut, for LOOSENING.
I have taken the liberty of modifying this photo I obtained from Randy, see theTWO RED arrows showing force direction.
HINT: that flat spanner dogbone wrench can be put over the damper rod (on some models), or otherwise slipped over the cap nut (many models), and you will NOT have handlebar interference, if the flat end of the spanner is THINNED a bit. Do that on a grinding wheel and DO NOT thin very much, and DO NOT take the temper out of the metal by getting it too hot. With the spanner now able to fit, in almost every instance, it may not be necessary to remove the handlebars from the top triple plate, nor even loosen them for steering adjustments. For cleaning and re-greasing, you do have to remove the bars, but still attached to the upper triple clamp! Another method of making an anti-torque tool is to use a pry bar or very strong screwdriver BETWEEN the handlebar mounts (leaving them in place for this).
Here are 4 more photos, that may be helpful to you. These are to give you ideas of various means to do the loosening and tightening of the center top cap and the fork tube caps, and the triple clamps, etc....so as to avoid or correct twisting, ETC.
The "procedure" continues after these photos.
This same squared-off end is
done to 27 mm or 1-1/16" sockets,
for the swing arm locknut. You can
use a short socket, as above photo,
for the front fork tubes' caps, and
with the wood piece as shown, the
cap can be hand-pressured so the
threads are not injured when removing
OR replacing the top cap.
A piece of bent pipe that is being used to apply torque in one direction, with the top triple clamp in place.
For torque applied the other direction:
**If you have not removed the ignition module (1981+) in a long time, cleaning and re-greasing it with heat sink compound... why not do this now?, after all, you have the fuel tank off, right? I suggest you clean the starter relay connections too, if you have the starter relay that plugs-in.
The bike must be jacked up a bit to have the front tire off the ground a couple of inches. You can jack it at the front of the engine, or perhaps at the front exhaust pipe crossover. The bike will rest on the center-stand and the rear tire. How this is done is up to you, and it may vary between bikes depending on tire size, suspension components, condition of those components. Some folks park the bike on a sidewalk, with the front end over the curb. On a flat floor, a specific problem will usually arise if you have a ride-off center stand. For such, I will usually jack the bike at the rear of the engine/transmission...or at the rear frame crossover...or the exhaust pipes (wood across them both) near the muffler junction. I have also, depending on the situation, placed a goodly sized piece of 1" thick plywood near the center stand, lined it up with my eyeball, and with the bike on the SIDEstand, place the plywood into needed position, and then straighten up the bike and engage the center stand UPON the plywood. This works well on ride-off stand equipped bikes. I have done all sorts of things to get the front wheel off the ground a couple of inches....on a few bikes with Reynolds RideOff stands, I have used locking straps at the rear suspension, to squeeze the rear suspension down...I usually add such straps from the lower shock units eye, up to some place like the luggage rack center area,,,,jump on the seat, whilst tightening the strap. The front wheel will now be quite far off the ground.
Block the front forks from dropping down too much, with wood or similar under the tire, if you need to.
5. Remove, being careful with that hammer on
the dogbone wrench! (if you need a hammer), the 36mm
hex tops from the top of each fork tube at the top of the upper triple clamp plate. USE an anti-torque
method. Be careful, use downward pressure, there may be substantial spring pressure here! It is
not necessary to remove the caps center allen head bolts, where you put oil into the forks normally.
With the left and right top caps removed, and the acorn nut removed, you can now lift the handlebar
assembly and tilt it enough to clear the damper rod (if you have one) in the stem . Fasten the
handlebar assembly forward against any windscreen, etc. or however; using some padding and a
long bungee cord wrapped around the windscreen...or just lay it forward, depends on the bike. It is
not necessary to remove the fork springs. So, at this point, you have a handlebar with controls &
cables & top triple as a total assembly lifted off the stem, & a front end ready to be dropped an inch
or more. Now you can remove the adjustment nut that was under that cap-nut using the BMW tool
kit wrench. Remove the dust shield. /5 models and late models are a bit different, but reasonably
self-explanatory. /5 models can be updated with the easier to adjust /6 type adjustment ring, etc.
6. You now must remove the block of wood or whatever, if anything, you had under the front tire. A
pull, sometimes a goodly JERK, from below, on the forks lowers, will release them downward a tad
(adjust wood under the fork as required). If need be use a piece of protective hardwood (not metal)
on the top of the steering stem, & the hammer, & give this a decent whack. When the fork drops
down, say a couple of inches, then adjust the wood block(s) below the forks to move the fork very
slightly up. This is necessary as the forks will have to be wobbily-moved-around a bit fore & aft %
sideways, during the cleaning & greasing operation, so you can get your cleaning rag, & finally your
greased fingertips, into the lower bearing area. The top bearing is right there & EASY to deal with.
7. EXTENSIVELY & THOROUGHLY CLEAN THE LOWER BEARING/RACE AREA.
free rags. I prefer old pieces of cotton bed sheets cut into strips about 1-1/2 or 2 inches by maybe
12 inches, so as to wrap well around the bearing during the cleaning. Use a small amount of a
solvent such as kerosene or paint thinner on the rag pieces. Do NOT use dripping wet amounts.
Clean as best you can the entire bearing, innards, the shell, & area surrounding. You should be able
to rotate the entire bearing, & get a good cleaning. Move the fork as required. Then a final cleaning
with a dry LINT FREE rag. Grease this lower bearing. I use my fingers & a LOT of grease, forcing
it up into the outer race & the bearing, rotating the bearing as required. You can not, easily, use
too much grease. You will need to use some finger pressure to force the grease into the bearing;
rotate the bearing, & push grease into it; & onto the outer race in the steering stem. Be generous
with the grease, you will clean the area up after final reassembly. Force as much grease as you
can, all around & into the lower bearing, & leave a goodly amount in the stem outer race area.
NOTE: If you have the hydraulic damper on your bike, this is a GOOD time to lubricate the plate/rack
area that drives the ball when the damper is adjusted from the top knob. You can put the knob
alone back in place on the damper rod, rotate the adjustment, get some oil/grease into that
plate/rack area at the very bottom of the lower triple clamp.
8. Remove the upper bearing rotating part, clean it & the cup/shell/race area. There should be no
roughness felt while rotating it. If there is, add a few drops of oil, if then OK, then the bearing, if it
LOOKS OK, probably is, so you can now hand grease the bearing, forcing grease throughout.
There is no good place for this note in this article that might not be confusing (as to where it applies in the 'procedure'), so I have placed it here. It is important that stiction not be introduced by your work, and any stiction minimized. Very early on in this article I described a test with the springs out, and advised that as you reinstalled them and the caps, that you recheck stiction. Depending on what you are doing to the front end of the Airhead, you may want to be testing for that stiction as you reassemble; during the steering head adjustment, during reinstalling of the fender or other braces and mounts and wheel assembly, brake, ...whatever, ...depending on what the various things you are doing to the bike. Do NOT let excessive stiction be in YOUR bike!
REASSEMBLY AND ADJUSTMENT:
Note: if you are cleaning & relubricating, & doing a quickie test to see if your bearings really are needing replacement, you can just install the adjustment threaded ring (other models have other adjustment methods) and make a simple temporary adjustment on the fork bearings, so you can feel the steering. You need NOT tighten the adjustor very much, so NO reverse-torque techniques are needed. You do NOT have to assemble the bars with the controls and cables assembly, etc. If you then find notchiness, undo the adjustor, remove the front end entirely, for new bearings. New bearings ALWAYS means a complete set of bearings with their matching outer races. NEVER replace just an inner bearing.
Assuming your tests are good:
1. Put top bearing,
shield cup, adjuster nut, etc., in place, lifting/blocking the fork upwards, then
tighten the adjuster nut, using the special hook wrench (or, whatever, depending on your model).
Wiggle the fork as need be. Attach the handlebar/top triple plate assembly. You should now be
able to attach the center top nut, or acorn cap nut, ETC., depending on your model. If that cap nut
has a ridge underneath that is to engage the hole in the top triple clamp plate, be SURE it fits into
the hole in the plate. Attach the fork top 36mm hex plugs/nuts with any washers. Doing this can take
considerable grunt against spring pressure; it will help to use a screwdriver (or?) into the allenbolt
recess to apply downward pressure. Do not cross-thread! HINT: It is easiest to start the top
hex plug caps with the front wheel/tire as low as it can go, yet high enough to enable a few
threads to be engaged. This means a minimum amount...three threads or so, of the center
NOTE: your bike may have a strange plastic spacer at
the top of the springs. That spacer is
formed to fit to the cut end of the coiled spring, so be sure it is put onto the spring
properly...LOOK at it, and see how it goes together. SOME people use a piece of PVC pipe
(or metal spacer) at the top to provide extra preload, I am NOT talking about that here.
NOTE that those using pieces of pipe, etc., for "preload" are REALLY changing the SAG of
the front end. Be SURE you know what you are doing if playing with spacers.
DO NOT FAIL to loosen the lower yoke (lower triple-tree casting)
Allen bolts, that
the clamping pressure on the fork tubes. Do NOT loosen those lower yolk pinch bolts before
having top nuts in place. The usual reason to loosen, and later retighten, those lower triple side-
clamping-bolts, is to allow the tubes to move ever so slightly, as you adjust the top bearing. Do
NOT forget to tighten them after you are done.
Be sure all is
lined-up correctly and tighten the two 36mm hex fork tube plugs to a small fraction of
a turn LOOSE from hand-wrenching tight. No need for the anti-torque tool right now unless you
want to;...you are NOT tightening to the limit. I DO use the anti-torque tool, taking no chances here.
2. Tighten the adjustment nut, that is UNDER the top
plate (late models are done differently), rather
tightly, moving the fork back and forth to take up any grease spacing. Loosen, and retighten
moderately tight. You now have to tighten the top acorn cap, as tightening it will tighten up the
adjustment of the steering stem....see later herein. You DO need the anti-torque tool for this, as the
acorn nut, whilst not 100% tightened in this step, DOES need VERY substantial tightening, to
remove the 'play' in the ADJUSTOR'S threads. SO.....you need NOT make this the final tightening at
this time, which is QUITE tight; still, that center top cap must be rather tight. Maximum hand effort
is about right, using the dogbone wrench, and the anti-torque tool...and NOT with the forks
against mechanical stops!.
NOTE: Most acorn capnuts have a ridge along its bottom, that MUST fit into the top triple clamp
hole...be sure it does!...if you do NOT have that properly assembled, you will bend things!
The motorcycle should be on the center stand and the front
not touching the ground, nor any
block of wood, etc. If the forks flop easily to one side, unscrew the top cap, tighten the underside
adjustment, retighten the top cap. Try to get the forks so they JUST won't fall to one side by
themselves; move the forks lightly from stop to stop to distribute the grease better, and try again.
3. Inspect to be sure that wiring, cables, etc., do not interfere with front end movement. Assemble
everything except, generally, the gas tank and steering damper and pod. Leave the lower triple
clamp allen clamp screws loose for now, but tighten up the top triple plate at the fork tube 36 mm
hextops. You NEED the anti-torque tool. The motorcycle should still be on the center stand and
the front tire not touching the ground, and NO block of wood, etc.
4. The first try for a final adjustment, for motorcycle, not sidecar use, should be to the point that the
front end exhibits a SMALL amount of perceptible drag. The only friction should be from stem
bearing grease, a small amount of bearing drag, fork tubes rubber boots if you have those, and
cables/wiring. Give a 'rap' on a handlebar end, using your palm. This should be of sufficient force to
move the handlebar about an inch or more, but not go flying to the stops. The handlebar will
probably tend to just barely reverse direction a TEENY amount, or not quite, after such a rap.
Another way of looking at this is that the steering, once somewhat to one side or the other from
center, should want to not really quite fall to the side, especially if nudged. You must temper this
idea with friction from cables and the rubber fairing boots, etc. It is a bit better to start from a bit
too tight, as that will be seen as weaving at low speeds, and a heavy feeling to handling. Your
bike will vary SLIGHTLY from other Airheads, in this adjustment. GENERALLY, you will want the
forks on such as the G/S and R80ST and most naked (no fairing) bikes to just fall almost all (or
actually all) the way to one side, but not so on the RS, RT, both of which need to be a bit stiffer.
Those with sidecars attached should set the steering head tighter than even the RS/RT as noted;
there must be NO tendency for the fork to continue to move towards the stops, or to fall to one side
or the other after being nudged on a sidecar rig. This is quite important for sidecarists.
At this point, turn the bars slowly from fully right
to fully left. If you feel roughness or a center notch,
you need new bearings and races!
this point tighten the top 36 mm fork nuts & cap nut FULLY...as tightly as you can with your hand
& the flat wrench, & then several tads more with the hammer. USE the anti-torque tool. The center
cap nut has to be near final tightness. You will notice the capnut has a major effect on the
adjustment nut setting, so loosen the capnut and readjust the adjustment nut, retighten the
capnut....until conditions are correct, with how that fork moves when nudged.
6. Final check, with the CAP nut tight, if you turn the bars one way or the other, from the
position, & nudge them, they should NOT QUITE fall very much, just a small amount on RS/RT, &
DO just barely fall to one side on other models. Some may want it a bit lighter, have the fork JUST
fall, almost fully or fully, to one side, but NOT too easily. Those with no fairing boots will likely want
it a tad looser. A tad of friction is better, but if it causes more than a WEE bit of weaving at low
low speeds, it is too tight. Those with GS & ST bikes may not want weaving at low speeds.
Special NOTE!....Again I caution against NOT using
the anti-torque tool.......and do not tighten
things with a big grunt, such that the fork is at full left or full right mechanical stop whilst
doing that tightening. It is possible to twist the forks out of alignment!
7. Assuming you don't need bearings & races,
is the time to, and you MUST!!; tighten the lower
fork triple clamp allen bolts
8. Assemble damper, pod, gas tank. Again check that all looks OK, no
cables interfere with steering,
9. If you have a fairing &
are assembling the hydraulic damper, with those pesky wire clip keepers, you
will need patience & likely a small inspection mirror. Grease those ball ends before assembling
the damper. Put a tiny amount of contact cleaner or silicon spray onto the instrument pod electrical
plug contacts, & don't forget the screw that holds that plug in place (and do not over-tighten it).
10. AGAIN, recheck all those bolts, screws, etc.
You DID tighten the lower triple clamps? Fork tops?
Did not get any cables crossed over or in such a position that the steering is not free???
11. The rear swing arm must be adjusted
correctly. If not, the motorcycle will not behave
properly during your test ride.
To adjust the swing arm, first insert the pivot pins (if not already), & tighten very
lightly with an allen
wrench (NOT a torque wrench). Go back & forth between left & right pivot pins until the spacing
from the swing arm to frame is approximately the same, as seen with your eyeball, or using a drill
shank or small allen wrench as gauges. Approximate is OK for this first step. This approximately
centers the swing arm in the frame. Install the locknuts (if not already) on the pins with your fingers
or the modified 27 mm or modified 1-1/16" socket (see below on the socket modification. The nut,
at this point, should NOT be tightened, but maybe a couple turns loose.
ONE side pivot pin allen (hex hole) clockwise to 15 ftlbs. Back off from the 15 setting maybe
half a turn, then re-torque IN clockwise movement (only) to 7-1/2 ftlbs.
Check the spacing from frame to swing arm. See if it is the same, left and
right. If not, back off one
pivot pin & tighten the other. Remember, clockwise movement during the tightening to 7-1/2 ftlbs.
When the spacing is the same, then tighten ONE of the locknuts to 72 ftlbs of torque. Recheck the
spacing. If still OK, then torque the other side's nut to 72 ftlbs. If the pivot pin and nut threads are
in good condition, the tightening of this fine threaded nut will NOT cause the pivot pin to rotate
during the 72 ftlb torqueing. If you are worried about that, put a mark on the pivot pin face and
associated frame opening, so you can see if the pivot pin moved after you tightened the nut.
The final step is to force grease into the hex holes with a rubber tipped grease
gun. I prefer to
force enough into the bearing, and out into the area between frame and swing arm, to be able to
smooth it into a ring of grease, with my finger tip. This will keep water and dirt out of the bearing.
Grease the same way every now and then.
The socket: You
can use a 27 mm or 1-1/16" socket. The socket MUST be modified by
the END FLAT AND SQUARE, enough so there is no taper on the inside, as the 27 mm nut is thin
and you do NOT want to damage the nut. Grind the OUTside of the socket, and do this squarely,
where it fits into the swing arm cavity... so that the socket goes past
12. Inflate tires properly. Remove saddlebags, and any rear trunk if not too much a bother.
13. Road test without passenger (passenger weight can
modify the effects you are going to be looking
for). Saddlebags, top boxes, & fairings/windscreens for that matter, have a noticeable effect on
high speed 'weaving', rather noticeable on downhill sweepers at around 85 mph. This high speed
weaving is NOT the weaving we will be trying to adjust out!...which is low speed weaving, as it is
normally thought of.
SO: The first road test is for low speed weaving.
Do this on a flat road, not uphill or downhill.
For ALL these road tests, ANY damper MUST be off! You will likely want to do this test at about
30 mph. Do NOT do it at 50+. If your steering bearing adjustment is too tight, you will find the
steering a bit heavy, a tendency to weave & not track smoothly, particularly in turns. If you have
this condition, remove the gas tank to protect it, loosen the top capnut (use the anti-torque tool!)
loosen the adjuster nut a small amount, perhaps a few degrees. Retighten the top cap (use the
anti-torque tool!), put on the tank, do another test. You do not have to loosen & then re-tighten the
lower triple clamp bolts unless you make nearly a full flat adjustment change; which should be
unlikely. Since the bikes top parts vary, a full flat means 60 degrees here. If you DO loosen the
lower triple clamp bolts in order to make a top adjustment, be absolutely sure you retighten them
before you go riding! If things feel correct in the 20-40mph range, try removing hands from the bars
and giving the bars a small hit one way or the other, at about 35 mph. Any tendency for an
INcreasing oscillation is cause for investigating tire balance, tire condition, even wheel bearings, etc.
Any slight oscillation (also called a wobble) should be damped out instantly with the hands back on
the bars. If not, you have a problem to look into.
High Speed tests:
I have almost never seen an Airhead with properly adjusted steering head have a problem at high speeds. However, it is possible, & things like large bar-mounted windscreens; bad tires, poor wheel bearings, etc., can cause problems. The worst case might be loose steering head bearings and a short wheelbase /5, with a bars-mounted windshield or bars-mounted fairing.
15. High speed tests are not for the faint-of-heart. They are usually
done by beginning at around 40mph
and increasing in increments of testing up to about 90. Every 10 mph, take hands off bars and tap
them a tad, which causes the bike to turn a bit, and check stability.
16. Airheads, particularly the old ones with two sided swing arms,
have an effect called, among other
names, Rubber Cow, Gummikuh, or a hinged-in-the-middle feeling. This effect is a weaving feeling,
often a nasty one on the RS & RT models with bags & especially with a large backrest/tour trunk,
at around 80 mph+, in downhill sweeping turns. This effect is primarily caused by wind effects on
those accessories, and the not very stiff rear suspension & the frame design, particularly the rear
sub-frame. BMW improved this with the single sided swing arm and elimination of the earlier style
of rear sub-frame, & further improvement is possible with better shocks, springs, & modifications to
stiffen the frame (the modifications of welding tubes to the swing arm are generally
17. It is FAR better to have the forks very slightly too tight at the
adjuster nut, putting up with slight low
speed weaving, than too loose. The reason is that if too loose you MAY have a chance of a high
speed wobble. This statement is worth extra notice on the SWB /5 bikes. Once you have done
this procedure & have the steering adjusted correctly, you likely will get it correct the next
time without having to do these road tests. I suggest you check the steering adjustment,
now that the bike road tests perfectly, by having the front tire off the ground, & nudging
the steering each way, & thereby see, for YOUR bike, just how much friction & movement
occurs. The next time you do your steering bearing service, simply adjust for this same
Fork Internals....MORE HINTS!
***The early forks contain what BMW calls "wiper rings" buried inside the mechanism. These look like small versions of common piston rings. I HIGHLY RECOMMEND that you do NOT replace them. New rings from BMW are NOT properly made, do NOT fit correctly, give too much friction, and OLD ones generally will work BETTER than new ones, since they slide easier. Any minor extra oil leakage due to wear is usually MINIMAL!
The internals of the forks vary between models and years. This section does not deal directly with the forks from the late eighties to the end of production, as things were much more standardized, for lack of a better word here. Further, the various sketches and diagrams available on various dealership's websites are not in full agreement with old manuals, such as the SNABB Katalog. Instead of writing a VERY long and extensive article, I will give enough hints and advice here, that you will be able to overhaul your own forks, and likely modify them, if so inclined.
You may want to take a look at http://mysite.verizon.net/vze4dp63/bmwmotorcycleparts/forks1.html
John Chay, who manufactures the Airhead cylinder stud threaded hole repair jig, has a fair amount of information on various parts for early and late Airhead fork parts, Works Performance Springs, etc.
Pressing in the top stanchion seal is sometimes a
hassle. Try heating the stanchion to around water-boiling
temperature, and if you do not have the proper BMW tool, use an
BMW has had at least FOUR service bulletins on the new style internals front forks that appeared in 1981. I will give only some summary information here.
First bulletin: Prior to the 1981 model, BMW offered a heavy duty front fork spring number 31-42-1-232-017 for use when fairings were installed...BMW did this themselves for the RS and RT models. For 1981 BMW added a SPACER, rather than change the fork spring. The spacer is also called an Intermediate Ring, and is part 31-42-1-241-737. You need two of them for the bike. You then needed a longer bolt, and the bolt at the fork bottom was changed to a M12 x 40, part 07-11-9-919-767, and you should replace the associated seal ring used with that bolt, and it is a 12 x 15.5, part number 07-11-9-963-130.
Bulletin of July 1982: BMW tried to fix front fork CLICKING NOISE. The bulletin was 31 007 82 (2046). This bulletin advised the fitting of shims, which were available in various sizes from 0.5 to 1.1 mm thickness, to remove the play between the valve housing and the retaining circlip. One was to use one or more shims as required. There was a circlip unit change, as the earlier one with tongues to keep the damper body from moving was not doing its job.
Another part of this bulletin was for fork spring rattling inside the fork tube. There was supposed to be a white nylon plastic spacer used on BOTH ENDS of the spring. Implied was that if one or both were missing, they were to be installed.
The Bulletin of August 1983 31 009 83 (2082) advised that for all models EXCEPT the R65 and R65LS, the fork dampers were now changed. NO LONGER were the shims, see above paragraph, being used. The fix by BMW was with a new spring-loaded valve housing, which eliminated axial play that caused noises. NOTE!.....the valve washer has a CHAMFER....the chamfer is installed TOWARDS THE PERFORATED DISC. BMW advised that whenever the forks lacking this updated valve housing were serviced, that it be installed. The backside of the bulletin had a sketch of the valve disk washer, housing, spring, ring, and retaining ring, as how fitted. The backside also had a sketch of the special tool to compress the valve housing spring so you can install the retaining ring. You can improvise something.
The Bulletin (these are called SI's by BMW
mechanics...as the title is Service-Information) of July 1983 was
strictly to show a revised fork oil amount for all the models,
and a list of approved fork oils.
The 1981+ forks have a rubber washer in the damper valve. Remove and discard. The may be a spacer in the bottom (RS/RT) that raises the fork height. If you fit new springs, especially aftermarket ones, and the height/sag is wrong, remove the spacer. Be sure the compression dampening piston is TIGHT on the damper rod, and use Loctite Blue on these.
re: Damper rings 31-42-1-234-506 and
31-42-1-232-045: You will see these items listed on
sketches, and they are used in two places on each fork side.
The top one is for compression damping, used with the holes
(orifices) in the rod. After the fork is compressed, it
will rebound, and the spring-loaded disc keeps the center
passageway from providing oil movement, so the rebound damping is
from what oil that moves between the damper rod and the LOWER
damper ring. The 3 pieces involved were
originally just 1 threaded ring, so don't get confused by the
various diagrams and sketches. BMW has a nasty habit of
showing, on its sketches, every part ever used.
There are two types of damper rings used for the LOWER rings...so, yes, that means two types of REBOUND types. The normal force ring is 31-42-1-232-045, and on most sketches this is item #9. Just below, on most sketches, is item #10. BMW's information on what is used on what models can be very confusing with the forks.
Ring -506 is called the STRINGENT ring by BMW (more dampening, the SPORT ring that is), it is identified by the groove that is machined on the outside diameter...which is used only for identification purposes (in the same way that the valve seat inserts have a groove marking for the cylinder heads, for the change in valve seat material, from 1985). The -506 damper ring also can be identified by its smaller inside diameter, which is 15.5 mm (the standard ring, the -045, is 15.7 mm inside diameter).
Again...BOTH RINGS ARE NOT USED AT THIS POINT. One uses either the Stringent -506, or the standard -045, at the LOWER position.
THE TOP RING IS ALWAYS THE -045. ...two are used on the bike.
NOTE: the -045 damper ring is not used on
stock /5 front forks. On the /6, it subs for the
So...what rings should you use? If you have the heavy duty front fork springs from BMW, 31-42-1-232-017, then use the -506 damper rings. NOTE that slightly heavier oil might be a good idea with this combination. Maybe an equivalent 7 SAE. Note also, that these -017 fork springs can sometimes be identified by having a white paint marking. They are 4-1/4 mm in coil diameter; and the length, when new, is 543 mm. The other springs, the slightly softer ones, are 31-42-1-231-358, and they have 4.0 mm coils, and when new have a length of 567 mm...yes, that is correct, they are LONGER, yet SOFTER.
For the /5 bikes, some modifications can be done that can be very helpful. Using the floating rings, and updated threaded rings, and braze closed one or preferably two of the rod holes (there are 4 total in each rod).
HINTs: Some sketches may show an O-ring, or
or it might be 31-42-1-232-763. Some sketches may show a 31-42-2-000-384, typically as item #7, a bumper, located below the spring. The sketch, as noted above, can be confusing. The damper piston goes between the spring and the bumper cushion. When disassembling, you'll likely find that bumper is around the rod. The bumpers deteriorate. The FLAT SIDE goes UP.
Don't willy-nilly change parts unless you THINK first. If you mostly ride on smooth roads, and are heavy, then I would suggest the Stringent damper rings, slightly heavier oil, and the -017 springs. Some very aggressive and lighter riders might like the changes too....especially if coupled with a stiff custom top triple clamp. If your roads are rather bumpy, you might find, especially if a lighter weight rider, that the heavy duty springs and stringent damper rings are too much, and the ride will be too stiff, and not work well on the bumpy roads.
NOTE!.....after 1980, these part numbers and usage do not apply like I have shown here!
Notes, addendum, etc:
A word of caution here about high speed diverging fork oscillations/wobbles. Due to gyroscopic and other effects, these forces at speed are fairly high. If a serious wobble begins, & forceful hands-on-bars pressure does not diminish or eliminate the wobble, you may well have a SPECTACULAR accident. If you have adjusted your fork steering head bearings correctly, any induced oscillation from the steering head bearings will be dampened easily. If your tires are road crowned, under inflated, way out of balance, etc., you can still have an oscillation problem.PLEASE DO NOT DO HIGH SPEED TESTS ON A MOTORCYCLE WITH A WORN REAR TIRE SUCH THAT THE CENTER OF THAT TIRE IS SHAPED RATHER FLAT, AS OPPOSED TO SOMEWHAT ROUNDED.
Approach road tests
carefully, deliberately, in stages, slowly increase the speed from one
test to the next test. Do not suddenly jump from a 40 mph test speed to 80
I have sometimes been asked if the steering head bearings have an official preload adjustment specification. YES, they do. The factory uses a tool that allows a torque wrench to be applied to the steering head top nut area. The factory specification is, believe it or not, different for the drum and disc brake models!! I have some ideas on why that is, but no proof. Be my guest in trying to figure out why there are two specifications.
For the drum brake front ends, the steering head is to be at 1.9 +-0.2
For the single or dual disc brake front ends, the steering head is to be at 2.6 +-0.14 footpounds.
It IS possible to modify the dogbone wrench to enable
an inch-pound wrench to be used. Yes, use above figures and multiply by
12. I have tried using a torque wrench, and it does work out OK, but not as good as with road testing & adjustment from those road
tests. I also have found that since the cables are almost
certainly not going to be disconnected, nor wiring disconnected,
that all have an effect on the steering, so that about 4 ftlbs was about correct.
The procedures in this long article have been abbreviated in places & expanded
in others. If you follow them, make notes for your own particular
machine. The differences between Airhead models and years is
mostly adjustment parts. Yes, there are variances in
washers, nuts, adjustments, split ring...etc....but the basics & what
you want to end up with, are the same. Steering head bearing and
lubrication should be done every 30K or so....OR, when you feel center notchiness.
BEST to do it BEFORE such notchiness is felt. Non-faired models ridden in wet weather may find the need
to do this more often, hence the reason I selected a long life grease
having great resistance to water. Having steering head set much too loose
will almost surely cause bearing damage and lousy handling.
Just HOW MUCH drag you should set the steering bearing preload for, is often a question. Generally, the drag is set rather HIGH for sidecar use. As I have mentioned in this article, for road use by a RS or RT, probably just a wee bit tighter than allows the fork to fall to one side, when nudged. An ST, G/S, S, and many other Airheads...and K bikes....are set so the forks will JUST fall to one side if nudged.
The headlight fork tube ears, at the top, just under the top triple clamp, have rubber bushings...a sort of rubber O-ring. FOUR sizes were made!..you need to use the one that fits properly on your bike.
31-42-1-232-527 is 3 mm thick
31-42-1-230-696 is 4 mm thick
31-42-1-230-697 is 5 mm thick
31-42-1-230-698 is 6 mm thick
There is also a rubber bushing or O-ring, located at the BOTTOM of the headlight ears. That one is only of ONE type and part number: 31-42-2-000-385.
Springs: The BMW heavy duty springs are OK. I prefer them to the Progressive BRAND of springs.
The Hyper-Pro progressively-wound springs are the springs I like the best.
Now and then I find something from my early lost articles notes:
I did extensive rework of the /5 forks decades ago. TWO modifications are going to make the dampening stiffer...in both directions. You can braze up one or two of the rod holes, and you can change the damper orifice to 15.5 mm, which is 31-42-234-506. In BMW's parts books, you will find the damper ring that is available in a heavier damping version to be called the 'more stringent' version.
© Copyright, 2014, R. Fleischer
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