Rebuilt forks = harsh mid-stroke on '06 yz125

Alright, when I first got this bike I was convinced the suspension couldn't be improved much. At about 145lb I fell just about in the intended rider weight range, and right out of the crate, the front end performed like no other tuned-suspension I had ridden with on other bikes.

But eventually the fork had to get leaky, and last weekend I replaced the seals and freshened the oil on both of the twin-chamber tubes. Took it out to the track yesterday and was pleased that there were no leaks, however I noticed the action had become A LOT harsher from the beginning to mid-stroke when going over acceleration bumps out of the turns. There was also tendency to deflect off of them-- which made jumps immediately out of corners just about teeth chattering on the approach.

Everywhere else the fork worked just as well, messed with the clickers (especially rebound) and that helped out some. Later on, I rode a buddies 96 CR125 for a few laps and even his clapped-out front end handled the little bumps better, so I knew something had to be wrong.

Anyway, I'm betting that it's because I added a tad more oil than the manual called for, thinking that it wouldn't hurt... doh. It's my understanding that the inner cartridge balances the excess oil out on it's own when pumping the air out... so do I just dump the oil out of the outer tubes and recycle with the correct amount? And does anyone have a good recommended level that may vary from the manual? It was my first time getting into suspension and I'm not too familiar with the field testing. :excuseme:

Three or four possible culprits.

1.) Too much oil in the outer chamber causing the air spring to be effective quicker in the stroke.

2.) Inner chamber not bled correctly.

3.) What oil did you use in the inner. Possible the wt(cst) was more than previous.

4.) Forks were reinstalled on the bike incorrectly.

Done wright even with stock valving these forks on that bike work really well for most motocrossers:ride:

If you're using stock springs and are not doing supercross or freestyle you should be able to get away with 300-320cc's in the outer chamber.

The inner chamber on these can be somewhat of a pain to bleed correctly. DaveJ has a good tutorial on here just do a search. I use a hybrid method but use a lot of steps from his way.

I would try and find a oil that is a true 3wt for the inner chambers. Something in the 16-18 cst@40.

And most importantly make sure your tubes are parallel when reinstalling on the bike.

Have fun:busted:

Oh and make sure you turn your rebound clicker to full soft before you tighten the jam nut on the cartridge rod to the rebound adjuster bolt. Make sure your jam nut is bottomed on the rod, thread your reb adj on, you'll see a small gap, tighten your jam nut up to the reb adj.

Set your clickers to 10-12 on compression and rebound. That should get you close to stock.

:excuseme:

You sir are a gentleman and a scholar. Thanks for the quick reply, and the oil I used was Motul 5w. Some people showed up at my place while I was bleeding the inners and I did the job on both of them while trying to carry on a conversation-- so you're right, I might not of payed the needed attention to get all the air out. Pretty sure the forks are level, so that couldn't be it.

Finding some 3w probably wont happen before I go to the track this weekend, but I'll keep that in mind next time I have to replace the seals/bushings. I'll probably try this again tomorrow after reading that tutorial and stay posted on how it works out.

"have fun," HA! I love working on bikes as much as the next guy but suspension turned out to be a different story... maybe it'll grow on me after a few more times. :excuseme:

From the textbook, viscosity has the most influence when put into a situation of substained shear. Oil flowing past a shim stack does not fall under this condition as the flow surface area to valve opening size is small, hense little shearing. It will, however, influence low speed adjustments as these are long, small dia passages where shear comes into play. Just some input.

Very good input indeed:worthy:

Alright, so upon tearing things down again.. I realized I left out a pretty crucial step-- completely compressing the damper rod after the the inner chamber was re-assembled to get the last bit of air out, so you were on the money. I took my time with the inner cartridge this time and re-filled the outers to 325cc.

Took my bike out to the track again today, pleasantly being rough as hell... MUCH better. Just rode the whole time without even thinking to fine tune with the clickers, maybe next time. Thanks again!

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now