Stiff forks after seal change

2004 WR450F. Had a leaky fork seal when I bought it.  It was of course wiped clean before I got there so didn't notice.  No idea how long it had been leaking or how much oil was actually left in it. Took the forks off replaced the seals with moose racing seals and fresh 5W oil.  At some point there was suspension work done to the bike.  The springs are way too heavy to be stock as I have never found a birt bike with stiff enough spring for me with stock springs.  I run 250-275.  These seem to be very close and give almost perfect sag for me.  The person I bought the bike from couldn't have done the change as his little 150LBS body would not have needed springs like it has.  I don't know what the valving is or what oil was in it.  The oil came out pretty dark.  Have no idea what the orignial color was but never remember seeing fresh fork oil that dark.  The damper rod could be moved by hand.  There was good resistance but it was smooth and was not so much resistance it was difficult to move.  No free play or binding in the bushings when moed without the spring.  No marks on the tubes.


Now After I did the seal change and the fresh oil the forks are really stiff.  Stiff enough for me to notice right away that they were stiffer than before the seal/oil change. As soon as I sat on it, not even a ride. I did make sure the forks are still parallel as close as I can measure.    The seals are good now with very clean dry tubes.


I guess I can change the compression dampening to see how it loosens up but I just find it odd that it was so much more stiff. HAve not had this off road yet as I was worried about how hard the forks were. 


So I guess the question is could I have messed something up to get this big of change, or was it just that bad before I did the seals/oil? What should I be checking? Beside compression damping anyway to make the start of the stroke more supple.



Edited by 300lbsgorilla

You went from zero viscostity oil to 5 viscostity oil, new bushings, new seals....

So it should be quite a bit noticeably different.

If you used anything but OEM or SKF seals, you would have also incresed fork stiction enough to notice it, as well (Tusk, Motosport, or any house brand seal)


10 hours later, judge it after break in.

Sorry I was under the impression that the stock yamalube 01 fork oil is 5W.  At least that is what I found seaching the forum. Several threads on the topic that typically come to that conclusion. Since I didn't know what was in there I decided to go with the stock weight oil.


I figured the seals may have more stiction but wow I didn't want to believe they were that much.  Now that I think about it I should have gone with SKF.  They are the only fork oil seals I will use on my mountain bikes but didn't even think about checking them for motorcycle forks.  Silly me.


Will break it in and see where it is.  If it is still this bad I will have to change to 0W and better seals.



Oil goes in 5w and comes out 0 weight, when it is worn out.  So, you were used to 0 wt oil.

Unlike inside a motor, fork oil is not about shear forces protection, it's about linearity of viscosity.

With forks, depending on how you ride, the oil can be done 10 hours or 100 hours of riding.

Once the oil gets really hot a few times, it is done, viscosity wise. 


Just like when you empty your crankcase: hot or cold, it comes out thinner than when you put it in, even if the oil is still working against the shearing forces.


The damping is designed around Yamaha 5w, which is really closer to 2.5w compared to Torco, or other premium oils.

Ok that makes much more sense.  Thank you for that.  Will just have to see how it breaks in.

Did you clean all of the internal parts real well? Perhaps some "sludge" is blocking the clicker orifices, and isn't allowing oil flow.

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