CB-650-Front Fork-Spacers?

 

My sagging front end on my 1981 Cb 650 will require some new fork oil
and will measure the spring too see how long a spacer can be installed
per fork. The actual washer size below the main top cap is 25.7mm and
I am wondering if anyone has some ideas, as to material that should be
used here for about a 1 to 1.5 inch thick spacer that can be used.
This bike also has 13lb air hose attachments per top cap, and
wondering if anyone has worked on these and can give me some advice
regarding removal of the threaded parts, turn top caps counter
clockwise for removal?
Thanks in advance  for any info.
Tim C.

 

Tim C wrote:

Throw out the original springs, they're sacked.  Progressive 11-1108
are $59.95 a set from:

  http://motodepot.com/street/suspension/psforksprings.html

You can use just about any rigid material for spacers, your static sag
should be about 1/3 of the suspension travel.  For short spacers, use
iron pipe fittings, 2p (UK) coins, silver dollars, etc. or you can use
PVC pipe.

The Honda workshop manual explains how to remove the air hose, there's
a slip joint in the middle that allows you to unscrew one side without
twisting the tube.  You won't need or want to use any air pressure after
you replace the springs, (air pressure preload is far less desireable than
using spring preload) but you will want to keep the fork tubes sealed.

Off the top of my head I'd say use 10W fork oil, 15W might work but will
be slightly stiffer than you're used to.

--
Mark  '01 SV650S  '86 GL1200A  '81 CM400T  '99 EX250-F13

 


Mark Olson wrote:


The problem with going from the stock springs with their original
length spacer is that Progressive will tell the purchaser to install
the longer progressively wound springs with no spacer at all, but they
won't give good info about the different required fork oil level...

The extra coils on the new progressively wound spring take up more of
the air space above the oil level than the original thin-walled sheet
metal spacers took up...

If you pour the correct volume of oil into the fork leg per the owner's
manual, the forks will probably hydraulically lock before reaching
their full stroke on compression. This could be disastrous if the rider
is in a turn and the forks hydraulically lock prematurely. When this
happens, the motorbike will head for the outside of the turn...

So less fork oil is required in each fork leg. How much less?
Progressive can't tell you, because they don't know, they apparently
never knew there was any problem at all until enough owners seemed to
have complained that something just wasn't right...

Whatever volume of oil is specified in the owner's manual no longer
matters. Progressive gives a rule of thumb about oil level from the top
of the fork tube to the oil level with the fork tubes compressed.

As I recall, they said to never leave less than about 150mm of air
space above the oil level...

If an owner keeps the original equipment springs and decides to
experiment with a set of longer preload spacers made from thicker PVC,
the same problem can happen, so the experimenter should know what he's
getting into...

The oil in the forks has to go somewhere, or the forks will stop
compressing on a bump. Maybe the excess oil will blow the oil seals out
of their seats and the naive experimenter will wonder what caused that
to happen...

Putting a few large washers or coins on top of the fork springs to
slightly preload the springs won't cause problems, though...

 

If those springs are origional they're long overdue for replacement.
(If you're carrying a few extra pounds or commonly ride two up  you
might want to select a stiffer than OEM spring. )
After a certain point spacers limit your fork travel and you're
probably past that point.
I strongly advise getting the spring  rate right before you start
messing with the damping rate. The two are interdependent,
but not  the same thing and trying to compensate for weak springs
 with a stiffer damping rate is not a good solution to your problem.
MadDog. - "R75/5 Forever!"

 



That's a hell of a lot. As Mark says, use coins (I have!), but I really
wouldn't go for that amount of pre-load. Half an inch is plenty.

Go for an inch and a half and you'll have fun trying to refit the fork
top nuts......



--
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