This page is about the BMW motorcycle models R50/US, R60/US, R69US, R50/5,
R60/5, R75/5, R50/6, R60/6, R75/6, R90/6, R90S, R60/7, R75/7, R80/7, R100/7,
This page is for changing BMW motorcycle fork seals and oil.
It is not to be used for changing the fork springs.
They are their own thing and I highly suggest that you refer to my page on
fork alignment. To just change
springs can get you in big trouble with fork alignment.
The fork seals should be changed when they are found to be leaking.
No huge safety problem exists because of leaky fork seals. If they
leak enough then maybe the dampening function of the forks would be lost.
By that time the whole front end would have been filthy dirty for years.
BMW motorcycle fork seal leakage test
You may test them for leaks often, it takes only seconds.
Learn the "feel."
Grab the boot midway (just above where you can feel the lower fork leg
casting) and pinch the rubber till you have the fork tube held in your fingers.
Now try to slide the boot up and down. A clean boot won't slide on a
clean tube. That means that the seal isn't leaking. An
oily boot will slide rather easily. To learn the difference, check
out several similar bikes at the next group gathering. Just go
around and try them. I have never tested 5 and found all of them to
be dry, you will find one, or more, that is easy to slide. It is
possible that someone replaced the seal, without cleaning or replacing the old
fork boots and now the inside of the boot is still oily.
If you want to see the seal for an even better and more accurate inspection
remove the lower clamp and lift the boot up as shown above. If you
see oil, then the seal is leaking to some extent.
Draining the fork oil the easy way.
1. Have the bike on the center stand with the front wheel in the
air. If you have a Reynolds stand you need to put a 2 X 4 under each
side to jack it up. The tire needs to be about 2" off of the floor,
unless you are going to remove it and then it only needs to clear slightly.
For safety reasons, tie the center stand forwards so that
the bike can't roll off of it.
Center stand tied in the "down" position for safety.
2. Remove the front wheel and set aside. This is only
necessary if you are changing the gators. If only the oil, then the
wheel may stay on and save time. It will be much heavier to lift the
assembly with the wheel back into place, but it can be done. For a
beginner I recommend removing the wheel. I like to remove the wheel
so that I can inspect the brakes too. By "the assembly" I mean the
fender, brace, rear fender brace, and fork legs or castings. It can
all stay bolted together and it saves time.
3. Remove the small black rubber dust covers from the bottom of
Screwdriver touching the cover
The dust cover
3. Remove the fork caps on the top.
That is the fork cap on the left and a cap wrench on the right.
If you look carefully you can see that one of the pins on my wrench fell out.
Now I improvise, until I find another one. Do not use a hammer and
punch. You can stick two drill bits in the holes and a lever between
them. The bits must be held firmly in place.
3. Get two containers ready to catch the fork oil. If
you have never done it this way before, then you are in for a surprise.
The oil is going to come out of there in two seconds. You must have
the catch containers ready and waiting. I use ones made out of two
old paper oil cans. I have a handle or hook that I hook over the
axle. There is little room for the oil to splash, as it goes
directly into the containers. If you use containers on the floor,
get them ready. Some of the oil will splash.
4. Look up under where the rubber dust cover was.
You will see this from below
Use a 4 mm Allan wrench to hold the center. Use a standard 13 mm offset
box end wrench on the nut. A
special tool is made by Joe
for this job and quite inexpensive.
Now it will look like this.
Hold the Allan wrench to keep the center from turning. Remove the
13 mm nut and washer from each side.
5. All that is holding the fork legs up is the jammed on crush
washers on each side. You can't see the crush washers at this time,
they are on the inside. See below. The fork springs are
now trying to shove the whole assembly down. If the wheel is off,
the boots will keep the assembly from falling all of the way to the floor.
Bump the fork brace downwards. The whole assembly will drop a couple
of inches and all of the oil will gush out almost instantly.
If you are only changing oil, then lift the assembly back up, attach the 13
mm nuts and washers. Be very careful to not
over tighten the 13 mm nut. They strip easily and maybe it
will be the nut and maybe the threads on the damper, not nice. Push
the rubber plugs back on, remove the top cap for fork oil filling.
That is what it looks like once the cap is off. Joe also makes a
tool for this job.
See the messed up fork retainer bolt? That is from some idiot using a Cresent
wrench and letting it slip off. Don't remove
that part, or you will have big troubles. It releases the
fork alignment. You will have a really big job ahead of you.
You can learn more about that job if you go to my page on
That's how you can put the oil back into the fork leg. Check your
book for the proper amount. It need not be exact, as it just isn't
critical. It is better to have 20 cc to little oil than too much.
I pre measure the fork oil in containers when I buy a gallon. It is
ready for future use. Wasn't that an easy job?
Many seem to want to replace the crush washers each time the fork oil is
changed. In the shop we didn't do it. There is really no
reason and only adds time and money to the customers bill. Some say
"Look at the deformed crush washers" and they are correct. They are
deformed, but the assembly goes back on and the deformed washer "forces" it back
the same way and it won't leak. If you want to replace the crush
washers, continue reading.
To replace the seals, crush washers, lower bumpers, damper rods or boots.
6. Loosen the upper boot clamps and slide the boots down and off
of the lower triple tree. The assembly can be lowered to the floor.
7. I like to use a helper at this point. One person
tilt the bike over about 1/2 way. That gives room for the other
person to drop the assembly out and away from the fork tubes. If you
have no helper, use a 4 X 6 on the floor to lay the cylinder head on.
The bike is only on it's side for a minute or so.
8. Remove the boots and replace. Replace the crush
washers if desired. They must be pried off as they will be really
stuck. It is a good idea and causes no harm. I seldom
replace them and they don't leak.
See the "smashed" copper colored crush washer? This is a
picture of the piston damper rod end.
9. While the legs are off this is a great time to test for fork
alignment. See my page on this
10. To get the seals out only requires a tire iron, pry bar or
lever, as in a screwdriver. Be careful not to scratch the aluminum.
Click on the photo and see how the seal is level.
To install the new seal I use the 3/4" drive socket that is a bit smaller
than the seal diameter. Keep it straight and gently drive it in
until it is flush with the metal.
Smear a drop of oil on the inside of each seal before re-installing the
assembly on the fork legs. If you are using the old boots that have
oil on the inside, clean them out or my test above won't work. They
will feel oily and indicating a bad seal, but it is new and not really leaking.
11. Reassemble in reverse order. Before you put the
wheel in place, check to see that the axle goes in totally freely.
Do not over tighten the axle nut, or you may
ruin your hub.
Tip for a longer boot (gator) life for your BMW motorcycle
I install my boots a bit differently than BMW intended. The bike
spends most of it's life on the center stand. The forks are extended
fully. This means that the boots are stretched out most of the time. That
causes them to crack in short order. The ones that you see in the
photos have been on that bike for 18 years and still look fine. I
fasten the lower clamp up to the highest point on the lower leg. It
looks a bit funny, but I don't care. I am lazy and cheap and will go
for the longer life.
BMW intended them to be mounted down at that lower ridge, not
at the top of the casting where it is shown.