Progressive Fork Springs
Installing Progressive Fork Springs on a BMW
by H.L.R. for webBikeWorld
After installing the
Progressive Suspension 420-Series rear
shock absorber on our 1986 BMW R65, we wanted to also revitalize the front
end with a set of Progressive Fork Springs.
The new-found control at the rear accentuated the front end's
slightly vague feeling, so we checked the Progressive
product lookup guide, which recommends the 11-1130 model springs for this bike.
And get this (believe it or not):
according to the sources we checked, the Progressive
11-1130 springs are also used in the 1988 to 1993
Harley-Davidson Sportster 883 and 1200; the 1987-1994
FXR and the 1935-1950 FXLR! Who said BMW and
Harley don't have a common heritage?
purchased a billet triple clamp from
San Jose BMW for our R65, and we'll report on that "one of these days" as
soon as we can find the time to get it installed.
problem is that our R65 has a different fork configuration than other
BMW motorcycles of the same vintage, and we were not able to figure out
how to install the new springs or the triple clamp.
The top fork nut is 41 mm across (see photo left), and it's threaded on to a 17 mm
Allen set screw. We tried removing the nut, but no amount of force
would budge it, even with a big cheater pipe on the end of the 1/2" drive
wrench. Something isn't right, but we could not figure out what.
We've been scratching our heads ever since on this until
wBW visitor "H.R." sent us this information, based on an installation of
Progressive Fork Springs on his nearly identical R65:
Progressive Fork Spring Installation
on BMW Monolever Motorcycles
This article documents the installation of
Progressive Suspension's fork springs on my 1986 BMW
R80RT Monolever. These forks are shared amongst
the R- and K- series bikes of this vintage.
The design is considerably different
from fork springs on earlier Airhead bikes. A
common error (OK, my error) when first encountering this
vintage of spring is to assume that all you need is the
right size socket to fit over the fork cap nut.
The monolever fork features a fork cap which is held in
by a circlip rather than threaded into the tube.
An advantage of this design is that it is no longer
necessary to use a "torque relief bar" when removing the
fork caps to prevent misalignment of the forks, but it
does require a bit more effort to get to the springs.
Read on for details...
Tools and Materials
You'll want the standard BMW tool kit if you're lucky
enough to have one. Some of the tool kits have the
required 41mm (1-5/8") ring wrench required for the fork
cap nut. Mine didn't and so I acquired a 1-5/8"
If you have the BMW wrench, you'll need
a breaker bar that fits over the wrench as the torque
required to loosen the cap nut is considerable. A
41mm socket will not work, as you'll just end up
spinning the cap and nut assembly together in the fork
A 17mm Allen wrench is required to fit in the fork cap,
or you can fashion one from a bolt and a few nuts as I
did (see picture). You'll also want some good
penetrating oil, and a propane torch is very handy.
My fork cap nuts were quite frozen after sitting on the
bike untouched for 20 years (not counting a previous
owner's botched attempt at removal), and heat is a stuck
nut's best friend.
Aluminum foil is handy for shielding the
local environment from the heat of the torch.
Other than the box-end and Allen wrenches only regular
hand tools are required. I found a 2-jaw gear
puller to be a nice alternative to a helper at a couple
of steps. A way to measure the fork oil in the
stanchion is required, and you can get creative here.
You'll also want a bottle of fork oil handy as you'll
probably be changing it at the same time you do this
A couple of days before surgery, apply your favorite
penetrating oil to the fork cap nuts. These tend
to be quite frozen to the fork caps and the longer they
soak, the easier your job will be.
Start by removing the gas tank and
handlebars. The bars just need to be unbolted from the
top triple and can just dangle out of the way.
While you don't really have to remove the tank, you'll
have more room to work and you'll avoid unsightly
After prying off the plastic caps on the
fork tops, you'll see the cap nuts threaded on the 17mm
Allen screws. Now get out the torch and aluminum
foil, shield any cables in the way, and get the cap nuts
HOT. Hopefully you'll see penetrating oil bubbling
out of the threads. Keep heating. After
they've cooled, you may want to repeat with more
penetrating oil. If you're changing the fork oil,
go ahead and drain it now. Measure the volume of
oil that drains out each side, and be sure to pump the
fork a couple of times to expel most of the oil.
The Fun Begins
At this point it's just a matter of inserting the
Allen wrench or bolt/breaker bar setup and putting the
box-end wrench over the cap nut. Then,
applying clockwise torque to the cap and
counter-clockwise torque to the box-end wrench,
heave-ho! A helper would be handy here, each
person cranking on one of the wrenches.
On my bike one of the nuts broke free
fairly easily; the other was apparently unwilling to
move. On the stubborn nut I reapplied heat and
oil, then turned the cap+nut assembly clockwise as a
whole (no Allen wrench) for about 1/4 turn. After
doing this and reapplying counter-torque with the Allen
wrench, the nut finally broke free.
With the cap nuts finally off, you'll need to depress
the fork caps an inch or so to get to the circlip that
holds the cap in the fork tube. Jack the bike up
under the engine to get the front wheel in the air.
A helper is again handy here, as is
patience, small screwdrivers or an icepick, and various
curse words. If you don't have a helper, a 2-jaw
gear puller clamped to the top triple can be used to
depress the fork cap while you fiddle with the circlip.
(see photo). Once the circlips are out the caps
pull right out of the tubes. Finally it's simply a
matter of pulling out the old springs.
Congratulations, the hard part is over!
New Spring Installation
Before installing the new springs, it's time to
adjust the fork oil level. The new springs, due to
their different winding, will displace a greater amount
of oil than the stock springs.
Hard-core engineer types will at this
point use a little calculus to find out the difference
in displacement, but for us mere mortals, the
installation guide simply recommends an oil level of 5
1/2" from the top of the fork tube to the oil with the
fork "collapsed". A better word is "compressed".
Use a helper, blocks of wood, or your wife's china to
compress the forks fully against their stops.
Now add oil to the proper level. As an alternative
to Progressive's $20 tool, I fashioned a fork oil level
adjuster from a syringe, some vinyl tubing, and a wire
to keep the tubing straight (see photo). Get
creative here or buy the special tool, your choice.
The manual for my R80RT recommends an
oil level of 320cc, and using the guidelines in the
installation guide I ended up with about 290cc of oil in
The oil level in the forks is not as
crucial as, say, the level in the engine sump, and it's
OK to experiment a bit here to dial in the response you
want in the forks. Use more oil to make the ride
firmer, and vice-versa to soften up the response.
Plus or minus ten percent is a good starting point.
On my bike the old springs were installed without a
spacer, but the installation notes that came with the
springs said to use the spacers provided. The
spacers are just 1" PVC pipe, but be sure to install the provided washers
between the spring and the spacer. The new springs
were longer than my old sacked out springs, and it's my
opinion that the spacer is optional or can be trimmed,
depending on whether you want a firm or plush ride.
I opted to include the spacer.
Be sure to clean off the new springs
first, mine had lots of "fluff" on them out of the box.
Now using your helper or the gear puller, depress the
cap nuts and reinstall the circlips. Finally
reattach the cap nuts using the box end and "Allen"
wrench. Having no way to measure the torque with
the tools I used, I just used anti-seize compound on the
threads and gobs of shoulder torque. Get them
At this point, it's just a matter of bolting up the
handlebars, reattaching the tank, and going for a test
I found with the new springs and 5W fork
oil, the ride was much firmer, but not uncomfortably so.
Front end dive on braking was drastically reduced, and
the handling is, while still stodgy old BMW in
character, noticeably improved. Again you can
experiment with oil viscosity and level to get the
response you want from the forks, but I personally would
stick with 5W and just under the stock oil level to
Enjoy your new springs!
Review: Progressive Suspension 11-1130 Fork Springs
Retail Price: $81.00 (pair)
Comments: Very nicely made shock absorber; looks like
custom made. Chromoly steel; rebuildable. Nitrogen gas
charged. Comes with cool-looking progressive rate springs in black
or red. Internal bladder eliminates need for external reservoir.
Five position damping adjustment. Threaded collar adjusts preload
but collar is a bit stiff and doesn't turn easily. Provides
excellent ride characteristics and gives very smooth but controlled
ride. Gives the bike's rear end a "silky buttery" feel without
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