'97 KX250 fork oil viscosity

[Burnt1Dragon]

Hi Everyone,

I have had a mechanic do the seals in my stock Kayaba's before now, and he had filled the tubes with 20wt synthetic.  Now, I have learned to and decided to do my own fork seals and noticed that the manual recommends 5-7wt? 

I know that racers often play with levels and viscosities in tuning practices, but I will not get any faster by tuning my forks by viscosity (I'll still be slow, lol).  My question is, is the higher wt oil hurt anything?  Seal life? Bushing life?  Is it really hurting performance?

I asked the mechanic who did them before and he sold me more 20wt, said it would not be any problem at all.  He runs 20wt in his newer 450CRF. 

What do you all think?

[Friar-Tuck]

 I am by no means an expert Dragon,
    (look at any previous post)
 Have you by any chance asked your Tech why he prefers 20wt?  The thickness of the oil (I think) would slow down the valve action & possibly have a better seal.  Other than that I would be interested in the reasoning.
  Are you a xxl sized person?  This may have something to do with using forks built for a 150lb guy and by merely thickening up the oil, even up the field for the shim stacks.   Heck, my '85 CR & XR service manual recommends ATF as a replacement for the forks. Now I understand those are a different animal, but Oil flow through shim stacks is oil flow through shim stacks...
    If it matters I use 5 and 7wt.  and would be interested in the theory.
         Here's an interesting chart a Brudda  sent me you might find of interest
                http://www.teamgreennews.ca/pdf/KX_Tech_Susp.pdf
 All these guys used was 5 & 10 wt.

and if your really board: http://www.pvdwiki.com/index.php?title=Suspension_Fluid
  Tuck\o/ 

[wayneh]

Fork oil viscosity is a matter of preference, riding style and weight. 20wt seems awfully heavy to me and will probably cause the fork action to very stiff especially on small and sharp edged bumps. I went to 7.5 in my 04 KX250 and might go back to 5 wt on the next change. Oil viscosity and oil level are two inexpensive ways to tune the forks to your liking providing the springs are right for your weight. Play around with it a bit and you'll learn to feel the difference.

Wayne

[bigbellybob]

my fork r filled with ATF