front fork sag


10 replies to this topic
  • Octanee

Posted August 19, 2011 - 06:12 PM

#1

hi guys, i got a question, today i pulled the upper part of the valve assembly out of my bike to change the springs for the merge RRS springs, i was thinking also in part maybe it would help with sag, so put it all back together and jump on it, and i had it set to soft for the first say 3-4 inches or so its really soft like, SAME AS THE STOCK SPRINGS NO CHANGE! basically sag im calling it, and then it gets hard like a fork should, when i turned it to get hard, same thing sags down EXCEPT it gets more harder when it does start to work,

what im wondering, is if the oil is low in my upper cartridge where the valve and spring is, could it be causing it to sort of sag like it has then start working? as if the oil gets pushed up to the valve and spring there then it starts to work?

Thanks! and it does return all teh way up, kinda as if a springs still pushing it back up, which i know the forks are supposed to have a big spring in the lower part of them which basically is what helps bring them back up or w/e, thanks!

  • grayracer513

Posted August 19, 2011 - 08:40 PM

#2

You may recall that I told you beforehand that those springs would not change the fork much at all by themselves.

http://www.thumperta...13#post10565613

The ICS springs do not directly support the weight of the bike to any significant degree, although they do add very slightly to the spring rate. As the damper rod enters the cartridge under compression, it displaces oil. That oil pushes up on the free piston against the ICS springs, and the piston moves only about 30mm total. The real purpose of the springs is to keep the piston pushing down on the oil supply in the inner (upper) chamber so that air can be excluded and the oil does not foam.

When ever the base valve assembly is removed from the top of the fork cartridge, it has to be bleed free of air when you put it back together. If you didn't do that, that would explain the lack of resistance at the top of the stroke, followed by a sudden increase.

Bleeding Fork Cartridges

  • Octanee

Posted August 19, 2011 - 09:06 PM

#3

You may recall that I told you beforehand that those springs would not change the fork much at all by themselves.

http://www.thumperta...13#post10565613

The ICS springs do not directly support the weight of the bike to any significant degree, although they do add very slightly to the spring rate. As the damper rod enters the cartridge under compression, it displaces oil. That oil pushes up on the free piston against the ICS springs, and the piston moves only about 30mm total. The real purpose of the springs is to keep the piston pushing down on the oil supply in the inner (upper) chamber so that air can be excluded and the oil does not foam.

When ever the base valve assembly is removed from the top of the fork cartridge, it has to be bleed free of air when you put it back together. If you didn't do that, that would explain the lack of resistance at the top of the stroke, followed by a sudden increase.

Bleeding Fork Cartridges


yeah i remember asking about the springs, i got them just because i figured hey it wouldnt hurt to try them and they were only 45 bucks, and i mean the forks have the same sag as they did before, no change with or without the springs, so i am wondering if its just because the cartridge oil is too low and so the forks compress until the oil hits the valve/the piston assembly or what it is, thats what i am asking

  • grayracer513

Posted August 20, 2011 - 06:54 AM

#4

Cartridge oil level does not affect fork sag, and neither do those springs. Only the main fork springs do that.

  • Octanee

Posted August 20, 2011 - 02:49 PM

#5

well i put oil in the upper cartridge and she pretty much fixed er up, no longer does it basically just go down like sagging and then it hits hard like it starts to work with the valving, now its maybe half the distance it used to go and then it starts to work with the valving, it wasnt like spring sag so much but when you hop on the bike right and push on the front it would like i said go down like 3-4 inches then stop as it seemed like the valving kicked in, so now by filling up more oil it goes down like 2 inches, which helps alot,

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  • grayracer513

Posted August 20, 2011 - 07:35 PM

#6

The way I read your posts, it sounds like you opened the cartridges while they were still in the fork. Did you?

  • Octanee

Posted August 20, 2011 - 10:11 PM

#7

The way I read your posts, it sounds like you opened the cartridges while they were still in the fork. Did you?


today, yes

seen videos of guys doing it and read about the installation of them merge rrs and stuff and they all saying that if you take it easy for a bit then it allows most of the air to escape up to that thing thats ontop of the fork to let out the pressure, since air is much thinner then oil is,

Edited by Octanee, August 20, 2011 - 11:05 PM.


  • grayracer513

Posted August 21, 2011 - 07:11 AM

#8

It doesn't work that way. That only way air can escape the cartridge is if the air is at the top of the cartridge when the cartridge is fully compressed. The bleed holes on the sides of the cartridge have to be oriented so that they are at the high point to allow the air out, and this may not be the case with the forks assembled. Besides that, air does not politely stay in a neat bubble at the very top waiting to pop through the bleed port and be gone, normal fork operation whips it into a fine foam that will eventually be distributed throughout the entire volume of oil.

The only way to correctly fill and bleed the cartridges is to follow the process I posted with the cartridges out of the fork.

  • Octanee

Posted August 21, 2011 - 08:30 AM

#9

It doesn't work that way. That only way air can escape the cartridge is if the air is at the top of the cartridge when the cartridge is fully compressed. The bleed holes on the sides of the cartridge have to be oriented so that they are at the high point to allow the air out, and this may not be the case with the forks assembled. Besides that, air does not politely stay in a neat bubble at the very top waiting to pop through the bleed port and be gone, normal fork operation whips it into a fine foam that will eventually be distributed throughout the entire volume of oil.

The only way to correctly fill and bleed the cartridges is to follow the process I posted with the cartridges out of the fork.


ok and when i take out the upper cartridge can i just put it back into my fork easilly or is like a take apart the whole fork kind of thing?, thanks

  • grayracer513

Posted August 21, 2011 - 09:26 AM

#10

Remove the forks from the clamps and do it right. Otherwise, they won't ever work right. You'll also need to refill the outer/lower chamber.

I'd recommend you find someone with some experience to help you out, or spend a good deal of time reading and understanding the information below.

http://www.yamahaown...ook.com.au/?r=0

http://www.thumperta...814#post8762814

http://www.thumperta...008#post8002008

  • Octanee

Posted August 21, 2011 - 09:57 PM

#11

alright, thanks!





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