It is advisable to read this article completely through before beginning
any work on the front end.
The exact procedure for various things varies 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
head bearings.
FORK OILS:
I prefer Spectro's fork oils, or suspension
fluids. They are GOOD, have low stiction, wide temperature range
(decent
to quite excellent viscosity index), and the viscosities can be depended upon.
NOTE that back in
early Airhead days, the oil used was "BMW red fork oil".
This oil was really a military hydraulic oil, you could find its
full specifications with a search engine for: MIL-H-5606E. Just to save
you the trouble, the viscosity specifications for that oil are:
MINimum 4.9 Cst at 100° C (generally accepted as 210°F)
MINimum 13.2 Cst at 40° C (100°F)
Maximum 600 Cst at -40° C ....too cold to bother
about, but it IS the spec.
You can use those two top lines to compare, perhaps!, with
other mfr's oils specs. ...and with the information in
article #52F on this site:
viscosity
(that is a hyperlink). DO NOT DEPEND ON MANUFACTURER'S SAE
NUMBERS...USE MY CHARTED INFORMATION!!!
Due to how specified, and lack of stiction
fighters and other characteristics, you are MUCH better off
with a REAL fork oil....especially a full synthetic fork oil.
For fork oils and suspension fluids,
the various manufacturer's do not agree on measuring
viscosity; and sometimes don't do more than give some
approximate SAE grade value. Viscosity measurements and
temperatures are vastly more cut and dried for engine and gear
oils, not so for suspension and fork oils. Because of this,
I highly recommend you stay with ONE
manufacturer if playing with different viscosity grades.
Except for some GS
models, all the old BMW's needed a very thin oil, roughly SAE 4 (that military
oil, as above), so do not willy-nilly change the viscosity
grade to too much higher....as only in the instance of VERY heavy
loads (rider and passenger weights and luggage)
is an oil heavier than an actual 7.5 weight of any benefit.
NEVER higher than SAE 10 for the non-GS models (some GS
models specifying use of different oil, say 10 and 15, in left and right
fork legs). I have other things to say about the GS in
the HINTS section near the end of this long article. A high viscosity INDEX is a good thing.
There is an article on this website on actual values for fork
oils...here is, again, that link (and it has other oil
information too):
viscosity
FORK SAG:
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
normally carried....).
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.
GATORS:
Folks are always asking about installing gators on Airheads that came with (OR
WITHOUT
them, such as on a RT). Gators DO protect the chrome fork tubes
from the little nicks they would otherwise get from oncoming
small rocks, gravel, etc...and 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
pin is.
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
Here is a relatively easy test for
stiction:
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.
Put
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, 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), then 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.
On many bikes, 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.
Bearings:
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
Classic K-bikes!
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.
Cleaning and re-greasing the
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?
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 much
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 adjustment procedure. 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.
Do not use greases containing moly (molybdenum disulfide)
compounds. My experience with moly is that it does
not work well over time 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,
but doable.
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 these bikes.
Enough information is available at:
http://www.largiader.com/bearings
The only major difference is the use of a sleeve tool; which, when properly
utilized, will eliminate the need for road tests (one hopes) with any minor
adjustments to find out if the initial adjustment was too loose or too tight.
**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).
2. If you have a damper knob, remove damper knob center screw, remove knob, spring, plastic
spacer.
3. 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 blad. 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.
4. 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.
5. 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, and 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.
6. Using a substantial sized hammer if you have to, and the BMW tool
kit 36mm
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; and the left hand is putting counter-torque on the
fork, using the pin and 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, and 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 happen, 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.
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 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.
7. 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 and
cables and top triple as a total assembly lifted off the stem, and a front end
ready to be dropped an inch or more.
8. Now you can remove
the adjustment nut that was under that capnut 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.
9. You now must remove the block of wood or what
ever, 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, and the
hammer, and 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 and afand sideways, during the cleaning and greasing
operation, so you can get your cleaning rag, and finally your greased
fingertips, into the lower bearing area. The top bearing is right there
and EASY to deal with.
10. EXTENSIVELY AND THOROUGHLY CLEAN THE LOWER BEARING/RACE AREA.
Use
lots of lint 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, and area surrounding. You should be able
to rotate the entire bearing, and 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 and
a LOT of grease, forcing it up into the outer race and 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, and push grease into it; and onto the outer race in the steering
stem. Be generous with the grease, you
will clean the area up after final reassembly. 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, and
rotate the adjustment, and get some oil/grease into that plate/rack area at the
very bottom of the lower triple clamp.
Force as much grease as
you can, all around and into the lower bearing, and leave a goodly amount in the
stem outer race area.
11. Remove the upper bearing, clean it and the cup/shell/race area.
Hand grease the bearing, forcing grease throughout. IF the bearing
has definite roughness after cleaning, lightly greasing, and now rotating and
visual inspection, you will probably need to replace the top and bottom bearings
and races....BUT!...you MAY be able to just continue with this procedure and get
reasonably decent steering bearing operation...so I suggest you continue.
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:
1. Put top bearing,
shield cup, adjuster nut, etc., in place, lifting/blocking the fork upwards, then
lightly 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 that 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!
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.
HINT: It is easiest to start the top hex plug
caps with the wheel 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 nut.
DO NOT FAIL to loosen the lower yoke (lower triple-tree casting)
Allen bolts, that
provide the clamping pressure on the fork tubes. Do
NOT loosen those
lower yolk pinch bolts before having some top nuts in place. The only
reason to loosen, and later retighten, those lower triple side bolts, is to
allow the tubes to move ever so slightly, as you adjust the top bearing.
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.
BUT....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,
which is QUITE tight, at this time; 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
tire 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,
but tighten up the top triple plate at the fork
tube 36mm hextops. You NEED the anti-torque tool.
4. The motorcycle should still be on the center stand and the front
tire not touching the ground, and NO block of
wood, etc.
5. The first try at 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, the forks on such as
the G/S and R80ST will tend to just fall almost all the way to one side, but not
so on the RS, RT, and so on. It varies some.
****Those with sidecars attached should set the steering head a bit tighter,
and 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.
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, so have a blue day!
6. At
this point, tighten the top 36 mm fork nuts and cap nut FULLY...as tightly as you can with your hand
and the flat wrench, and then several tads more with the hammer. USE the
anti-torque tool. The
center cap nut has
to be rather tight, almost to final tightness. You
will notice that this 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.
7. SO..... a final check,.... with the CAPnut tight, if you turn the bars one way or the other, from the
straight ahead position, and nudge them, they should NOT QUITE fall very much, just a small
amount. 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 speeds, it is too tight.
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!
8. Assuming you don't need bearings and races, NOW
is the time to.....and you MUST!!.... tighten the lower fork triple clamp allen bolts (don't even think of forgetting
this step!), and to do a thorough
check-over, to be sure you have assembled everything and tightened everything, except
assembling the hydraulic damper and instrument pod and gas tank.
9. Assemble damper, pod, gas tank. Again check that all looks OK, no
cables interfere with steering, etc. If you have a fairing and
are assembling the hydraulic damper, with those wire clip keepers, you
will need patience, and likely a small inspection mirror. Grease those
ball ends before assembling damper. Put a tiny amount of contact
cleaner or silicon spray onto the instrument pod electrical plug
contacts, and don't forget the screw that holds that plug in place (and
do not over tighten it).
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???
10. The rear swing arm must be adjusted
correctly. If not, the motorcycle will not behave properly during your test
ride.
11. To adjust the swing arm, assuming the swing arm is centered
or approximately so already at the frame: loosen one 27 mm locknut maybe half a
turn or a turn or so. Torque
that side's inner allen to 15 foot pounds. Back off from the 15 setting, re-torque to
7-1/2 ftlbs, ending up as torquing clockwise to
get this 7-1/2 setting.
Lock nut torque should be 72 ftlbs. The lockout is 27mm, the center
Allen is 6mm. Recheck centering (I use a drill shank or appropriate size of
allen wrench at the inside
junction of the swing arm to the frame as a gauge). NOTE that you
can use a 27 mm or a 1-1/16" socket. The socket should be modified by
grinding the END so there is no taper on the inside, as the 27 mm nut is
thin. Grind the OUTside of the socket, and do this squarely!.... where it fits into the swing arm
hole... so that the socket goes past any internal projections and then over the 27 mm nut completely and thoroughly.
SOME bikes have a second ridge inside the swing arm hole, so the socket must be ground
on the outside a wee bit further. If the swing arm is not centered,
back off one adjuster, and tighten the other, and when tightening the other,
again tighten in the clockwise direction until you reach 7-1/2 foot pounds.
Don't forget to tighten the swing arm adjustors locknuts.
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, and
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.
14. The first road test is for low speed weaving.
Do this on a flat road, not uphill or downhill. Don't do the testing in
turns, unless you have a fine feel for it. For ALL tests, the
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 and 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!) and 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 and then re-tighten the lower triple clamp bolts
unless you make nearly a full flat (or more) adjustment change. Since the bikes
top parts vary, that is 60 degrees meant 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!
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, and things
like large bar-mounted windscreens; bad tires, poor wheel bearings, etc., can
cause problems.
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, and check stability.
16. Airheads, particularly the old ones with two sided swing arms,
have an effect called, among other
names, Rubber Cow, or a hinged-in-the-middle feeling. This effect is a
weaving feeling, often pronounced on the RS and RT models with bags and
especially with a large backrest/tour trunk, at around 80 mph+, in downhill sweeping
turns. The effect is noticed, however, at some speed. This effect is primarily caused by wind effects on those
accessories, and the not very stiff rear suspension and frame design,
particularly the rear subframe.
BMW improved this with the single sided swing arm and further
improvement is possible with better shocks, springs, and modifications
to stiffen the frame (the modifications of welding tubes to the swing
arm are generally not of much use). Surprisingly, a good front fork brace can
help a bit. So can, especially, a thick top triple plate.
Aftermarket top triple plates are available. Some have modified lower triple's
for this, some have doubled up on the top plate; those are not as pretty. If your bike exhibits this
uncomfortable weaving feeling at
HIGH speed, particularly
downhill turns, it is likely not the steering head adjustment!
NOTE that a stiff aftermarket TOP triple clamp
plate will help much more than a fork brace (which are often not properly
installed and CAUSE problems with stiction)..
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.
Once you have done this procedure and
have the steering
adjusted correctly, you likely will get it right 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, and nudging the steering each way, and thereby see, for YOUR bike,
just how much friction and movement occurs. The next time you do your
steering bearing service, simply adjust for this same effect!
****NOTE: A word of caution
here about high speed diverging
fork oscillations/wobbles. Due to gyroscopic and
other effects, the forces at speed are fairly high. If a serious wobble
begins, and 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.
Approach road tests
carefully, deliberately, in stages, that is, slowly increase the speed from one
test to the next test. Do not suddenly jump from a 40 mph test speed to 80
mph.
****NOTE: 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
specifications is, believe it or not, different for the drum and disc brake
models!!:
For the drum brake front ends, the steering head is to be at 1.9 +-0.2
footpounds
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, or do some other thing, 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 and 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, that about 4 ftlbs was
about correct. It is tricky.
These procedures have been abbreviated in places and 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 and 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
HIGH for sidecar use, and 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.
Fork
Internals....HINTS!
WARNING!
***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 INTERNAL 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
appropriate-sized socket.
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
31-42-1-232-058.
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
washer, 31-42-1-240-027, 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!