Fork 'Popping'

[Wudscrasher]

Hi, fellow KDXers. New here, but have been lurking for awhile, getting loads
of great info from you all, so a big THANK YOU. I bought a 2000 KDX220 a month
or 2 ago, and have been tuning it up for the upcoming riding season. Last night,
I was replacing the oil in the forks. After filling the brake caliper fork, I was
pulling the slider up to get out air bubbles. At first, it was difficult to pull,
then it 'popped'and slid up normally. I pushed it back down, pulled it up about 2",
let go and it slid down, as if there was a vacuum pulling on it. I pulled again, and it
'popped' again. Is this normal for one of the forks to do this? The other one did not
exhibit this behavior. My friend who was helping me wondered, since there is no rebound
control, if it acts like a rebound control under severe bottoming. Obviously, the fork
shouldn't compress to the point where the slider hits the bottom of the lower tube, and
after reinstalling everything, the forks seem just fine. I was just curious if any of
you have experienced this phenomenon as well.

Thanks again, and ride smart!

-- C.J.

 

[canyncarvr]

re: 'I was pulling the slider up to get out air bubbles.'

What are you referring to as 'the slider'?

Bleeding the fork prior to setting the oil level will result in some bubbles being worked out of the hydraulic system...I wouldn't call them 'pops'.....but I wouldn't refer to the cartridge rod as 'the slider' either, so I'm missing something.

Rebound valving or not, there isn't any 'suction' going on when you release the rod. It drops of its own weight, displacing oil as it goes....but nothing 'pulls' it down.

Assume the noise you heard was air bubbles, that is normal. You should repeatedly pull/push the rod until there is no more 'popping'. Not a bad idea to tap the fork a few times with a rubber mallet during the process. The desired result is to hear NO such 'popping' when the rod is moved.

Set your level.

Oh..do that with spring out, forks collapsed.

Reassemble by holding the top cap and turning the tube..NOT by holding the tube and turning the cap.

Don't overlook the crimped-on spring seats (they should be on the bottom of your springs).

 

[Wudscrasher]

Sorry carvr, it's really hard to explain it right. I had the spring out, fork collapsed, to fill it. I pulled the inner rod up and the inner fork tube (not sure of the correct terminology - sorry), ie the part that slides into the triple clamps, to meet with the cap. It was the inner tube (and rod?), when being pulled up from fully collapsed, that this initial resistance was felt. Like I said, both forks seem to be equally suspended, it was just weird. As a side note, the caps do not have air bleeder valves. Can they be replaced with ones that do? Is it tremendously important, and is there a way to bleed air without removing the caps?

TIA

-- CJ

 

[canyncarvr]

re: 'I pulled the inner rod up and the inner fork tube..'

To bleed the fork, leave the tube down. Pull just the rod (up and down, repeatedly etc etc...)

re: 'It was the inner tube (and rod?), when being pulled up from fully collapsed, that this initial resistance was felt.'

Pulling up the tube by itself has no effect on the hydraulics of the fork. All you will feel is the tube moving in the sliders (bushings).

The 'resistance' you feel when you pump the rod will vary as the air works out of the fork. When you're done, the resistance will be even throughout the movement of the rod. Sure, the harder you pull, the more resistance there is. Liken that to a LSC hit and a HSC hit. When I say 'even' that does not mean 'the same' given different suspension component speed of movement.

I doubt anything you felt or describe is problematic. If you didn't bleed the forks properly, they will GET that way through use. The problem with that is the oil level in the two forks may not be the same....I doubt very much you would know the difference if that is true.

Don't worry about it.


re: 'Can they be replaced with ones that do?'

Yes. MotionPro makes a set of bleeders that will simply replace the screws already on the cap. Bleeders that screw into the existing threads are generally taller than bleeders that require the hole be re-tapped. The tall ones fit fine (below the bars). Well...not if you run your forks 1/2" up in the clamps.

re: 'Is it tremendously important...'

Opinions vary. Mine is it is very important. I used to think it was just me getting tired at the end of the day when my suspension was acting differently. It turned out being pressure buildup in the forks that was the problem. IMO, bleeders are essetial in the OEM KDX fork.

Besides, you can 'tune' your forks during the day, depending on what you're riding in at the time. Want more air-shock? Unload the forks, press the buttons. Want less? Load the forks, press the buttons.

re: 'and is there a way to bleed air without removing the caps?,

I hope this is self-evident at this point. Yes. Install some bleeders!

A side note. Carry the screws you take out with you. Very handy to replace a broken-off bleeder after you hang your bike in a tree. Consider what's going to happen if you cannot plug up the resulting (broken bleeder) hole! It's gonna get messy!

 

[Wudscrasher]

Thanks carvr, what you said makes sense.

About the MotionPro bleeder screws: my fork caps only have the compression adjuster screw, right in the middle of the cap. If I get a bleed valve, will I not be able to adjust compression at all, or is the MP unit both? :coocoo:

TIA

-- CJ

 

[canyncarvr]

Re: 'my fork caps only have the compression adjuster screw, right in the middle of the cap.'

That would be incorrect....wrong, even.

You do have only compression (no rebound) adjustment..LSC at that. The adjustment is in the base valve. The base valve on the bottom of the fork..the axle end...has a screw in its middle, too.

The screw in the cap is not an adjustment screw....it's just a brass screw with an o-ring wrapped around it. Remove it/them, screw in (for example) the MotionPro bleeder/poppers.


You're done.


Repeat from the other direction... No, the MotionPro bleeders are NOT 'both' adjuster and bleeder. They are only pressure relievers/bleeders. You will be able to make compression adjustment the same as you were able to before...by using the adjustment on the bottom of your fork leg.

...said screw is covered by a rubber plug thingy????....

 

[Wudscrasher]

Ahhh - it all makes sense now. Sweet!

re: ...said screw is covered by a rubber plug thingy????....

So THAT's what's under there...

Thanks a ton canyncarvr!

-- CJ