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Posted by Gixxerman on August 8, 2007, 5:03 am
Hi all,
I have been changing the oil to the forks of my gsx-r 600 k4, after re-
install it again in place, went to try it and its a big mess,
initially even with the standard settings the fork looks too stiff,
but under braking the front compress fully to the end of it, try to
give more preload in the spring, and it's the same.... other thing it
makes is, in higher speeds when hit the front lever, i feel a big
vibration......
I heard this can be caused by air inside the cartridge...
Any ideas?????
Thanks
Jaime
Portugal
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Posted by Albrecht via MotorcycleKB.com on August 8, 2007, 7:56 am
Gixxerman wrote:
>Hi all,
>
>I have been changing the oil to the forks of my gsx-r 600 k4, after re-
>install it again in place, went to try it and its a big mess,
>initially even with the standard settings the fork looks too stiff,
>but under braking the front compress fully to the end of it, try to
>give more preload in the spring, and it's the same....
What year is your GSXR? What do you weigh? The amount of sag recommended by
the magazines may work for light weight riders, but the springs are so light
what the magazines say won't work for heavy guys.
Modern fork design relies on compression damping to resist front end dive and
a lower rate spring for good compliance.
Rider weight becomes critical when such light springs are used, and
preloading the low rate spring to reduce sag just uses up fork travel.
I got this information from www.racetech.com > sportbike > spring rates
92-93 42.6 lbs/in .762 kg/mm
97 42.6 lbs/in .762 kg/mm
98-00 ask Race Tech
01-03 43.5 lbs/in .780 kg/mm
Take the 92-93 model as an example. With two 42.6 lb/in springs, it takes 85.
2 pounds of *static* force to compress the forks one inch.
If the fork stroke is 4.4 inches, it will only take 375 pounds of force to
bottom out the fork. If the motorcycle weighs 450 pounds and you weigh 200
pounds.
375/650 = 0.576 g's.
In other words, a 1/2 g stop is going to bottom your forks.
These are Race Tech's aftermarket springs. There is a spring rate calculator
on the website.
47.5 lbs/in .85kg/mm
50.3 lbs/in .90kg/mm
53.1 lbs/in .95kg/mm
55.88 lbs/in 1.0kgmm
61.5 lbs/in 1.1kgmm
67.0 lbs/in 1.2kgmm
>other thing it
>makes is, in higher speeds when hit the front lever, i feel a big
>vibration......
It could be loose steering head or wheel bearings or a warped/misaligned
front rotor or sticky brake pads.
> I heard this can be caused by air inside the cartridge...
That's possible. Refilling a cartridge fork with oil requires careful
attention to detail to get the oil into the cartridge and the air out.
--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/tech/200708/1
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Posted by Dave Emerson on August 10, 2007, 1:11 pm
> Hi all,
>
>
> I have been changing the oil to the forks of my gsx-r 600 k4, after re-
> install it again in place, went to try it and its a big mess,
> initially even with the standard settings the fork looks too stiff,
> but under braking the front compress fully to the end of it, try to
> give more preload in the spring, and it's the same.... other thing it
> makes is, in higher speeds when hit the front lever, i feel a big
> vibration......
> I heard this can be caused by air inside the cartridge...
>
> Any ideas?????
How much oil did you use?
Did you measure volume or oil or depth to level, if latter to/from what
point?
What weight of oil did you use?
--
Dave
ex Motorcycle Maintenance Workshop
http://tinyurl.com/4mhaw
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Posted by Albrecht via MotorcycleKB.com on August 13, 2007, 10:40 am
Gixxerman wrote:
>After some tests, the front is now working ok, but is still juddering
>when i brake harder under highest speeds, it guet's better when i
>close the rebound, but then it becames to stiff.
Dude...
If the front tire contact patch is chattering on the road surface, you need
to
decrease the *compression* damping, not increase the rebound damping.
But you have to have the correct springs for your weight.
You would increase the rebound damping if the fork was wallowing at low
frequency. Too much rebound damping with light springs can cause the fork to
"pump down" and become rigid when it bottoms.
I asked you before: WHAT DO YOU WEIGH? Have you been to the www.racetech.com
site to use their rider weight spring calculator program?
--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/tech/200708/1
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Posted by Gixxerman on August 13, 2007, 12:02 pm
> Gixxerman wrote:
> >After some tests, the front is now working ok, but is still juddering
> >when i brake harder under highest speeds, it guet's better when i
> >close the rebound, but then it becames to stiff.
>
> Dude...
>
> If the front tire contact patch is chattering on the road surface, you ne=
ed
> to
> decrease the *compression* damping, not increase the rebound damping.
>
> But you have to have the correct springs for your weight.
>
> You would increase the rebound damping if the fork was wallowing at low
> frequency. Too much rebound damping with light springs can cause the fork=
to
> "pump down" and become rigid when it bottoms.
>
> I asked you before: WHAT DO YOU WEIGH? Have you been to thewww.racetech.c=
om
> site to use their rider weight spring calculator program?
>
> --
> Message posted via MotorcycleKB.comhttp://www.motorcyclekb.com/Uwe/Forums=
.aspx/tech/200708/1
I haven't been to the www.racetech.com site, and my weight is 83 kg's
before i change the oil, the forks were working ok with the std
settings, after i change the oil they aren=B4t :-) ,
Probably to reduce the compression damping i have to add a little bit
more oil, because the front is still diving a lot, after that will try
it again to see how it feels, as soon the front is ok in matters of
compression, i will start to find the perfect rebound setting.
Jaime
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