Fork Oil Question

3 replies to this topic
  • c-man

Posted October 28, 2008 - 06:45 AM


Reading the manual of my 06' 450 last night in contemplation of changing fork seals/fluid. Looks like you fill the "inner fork cartridge" with fluid and then the outer tube with fluid. Anyone know how much mixing of this fluid there is? Is the inner component a sealed unit that maintains a constant amount of fluid, or does the amount in the inner cartridge vary as fluid moves in and out from the outer tube.



  • grayracer513

Posted October 28, 2008 - 07:46 AM


The design is for the fluids to remain separate. The inner cartridge is supposed to be purged of air, and has a piston and spring in it to separate air and oil. The outer chamber is then filled with a specific amount of oil for the purpose of lubing the forks, and for use in the hydraulic anti-bottoming forcing cones. Under most conditions, the fluids are kept separate from each other, and some, such as myself, use two different fluids. However, when the fork is bottomed, or nearly bottomed, the pressure against the cartridge seal is extremely high, and some oil can be forced past it from the outer to the inner chamber. The cartridge can deal with this, however, as it will self-bleed the excess back to the outer side once the level rises high enough, and the fork is fully compressed.

If using two differing fluids, and riding very hard, it's a good idea to change more often.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • c-man

Posted October 28, 2008 - 08:53 AM


Thanks....exactly the info I needed. Is one body of fluid under more abuse and subject to more breakdown than the other?? Does one need more often changing than the other??


  • grayracer513

Posted October 28, 2008 - 09:09 AM


I'd say it's about even for differing reasons. The inner cartridge oil is subject to greater shear forces, since it does almost all the damping work, while the outer oil becomes contaminated with wear metals from the springs rubbing on the insides of the tubes. The condition of the inners is probably more critical.

Related Content


Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Thinking about Yamaha 250... by Arctic Pride

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  491 replies

Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • - - - - -
  • 0 reviews

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.