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One of the great things about the /5 BMW was that it had such great
fork travel. It was even greater than most of the dirt bikes at the
time. The more that one uses a spacer to compress the fork springs, the
more one may lose fork travel. If you put in a 7-8" spacer, there would be
no fork travel left. The spring would effectively have been replaced with
a solid tube. A compressed spring is a solid tube.
Just how much of that highly prized fork travel are you
willing to lose? BMW used one spacer of about 5/8" in each side on
the US forks (1968/69) and probably one can compress the forks that far without
causing the springs to become fully compressed at full travel compression.
BMW used spacers made of aluminum, not PVC plastic. The plastic is
reported to get brittle and disintegrate over some years. The risk is
yours.
While most riders can lose 1/2" of travel and probably not notice, just about
none of us can lose 2" and not notice. A spring that needs to be
compressed with the use of spacers to get the desired tension is improperly
designed.
A common spring replacement is made by a company called Progressive.
BMW forks with Progressive springs can work for some riders. I suspect
that the springs are of good quality, but they are too short. They include
a spacer to make up for the short length. That just isn't a good idea.
BMW finally did away with the spacer for the same reason, it can waste fork
travel. In general, springs from Progressive weren't satisfactory for most
riders as they were a bit hard.
Many would swap out the older sacked out springs and use the ones from
Progressive. They would fail to do the job properly and discover that the
forks didn't work properly. The springs got the blame, not the job of
installing them. It seems simple, but is far from it.
BMW offers a heavy duty fork spring. It is actually about 3/4" shorter
than the weaker, but original spring. In time, a spring becomes compressed or
as we say, it is "sacked out". A sacked out spring will be much shorter
than when new. Check the BMW specification for proper length.
The alignment issue of BMW motorcycle forks.
If perfectly aligned forks had springs changed and the process of
installation isn't properly followed, it is most likely that the result will be
stiction. Don't confuse stiction with stiffer forks. They are
totally different. While stiffer forks may be desirable, stiction never
is. Stiction means a much greater chance of wobbles.
See my page on wobbles. If it doesn't scare you
to death, just ask any motorcycle rider that has been through a high speed
wobble and lived to tell about it.
Simple procedure for changing fork springs on a BMW motorcycle
To change the springs, most owner/mechanics remove the two top spring
retaining big nuts by turning the forks to one end of the travel, against the
stop, and loosening them. That may be OK only if you are willing to align
them upon reassembly. You CAN'T assemble them the same way that you took
them apart. The torque must never be transmitted through the triple clamp
for tightening. See my page on the fork alignment tools for details.
This is only one part of why people get such different results when changing
fork springs.
The very first thing to do is to check for stiction.
If you have the normal and desired amount of very little stiction, record your
measurement. When you finish changing fork springs, it should not have
increased. An increase definitely shows misalignment.
The safe way to change springs is to use a
torque relief arm for both removing the spring retainer nut, one at a time,
and torquing it up again. Then do the other one. If you loosen both
at the same time, then the whole assembly will be encouraged to relax into a
position that is out of alignment. It is risky to even loosen up one
spring retainer cap at a time and that is why you measure the stiction before
and after.
Just because it is such a big deal to align forks,
doesn't make it any less necessary.
This is the very best article on aligning forks,
with a step by step procedure. My thanks to Randy for writing this one up
so well.
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