06 YZ450 Fork oil change?

I've done the search and could not find my answer so I'm throwing this out there. It's time to change the oil in my 06's forks. The last forks I tore apart were off my 02 426's so needless to say the new ones are quite different. After reading the manual, I'm confident I can handle the task however, it does not specify an oil height for the outer chamber (only the inner cartridge)? Is everyone adding the recommended volume or is there a measurement listed somewhere and I just missed it??

The new ones do it differently. The outer chamber is filled by volume only, that is, with a specified amount. Be accurate there; as little as 5cc up ro down can make a difference in how the fork feels, according to reports I've read.

The oil level in the inner chamber is actually a minimum level. Any excess gets displaced during the insertion of the base valve, and is dumped off in step 13 on page 5-35. The curiously worded note on page 5-34, "First bring the damper rod pressure to a maximum. Then install the base valve while releasing the damper rod pressure", actually means that you need to compress the filled damper fully, start the base valve into its bore, and then press it into place while letting the damper extend. This is the process that purges the air from the cartridge. Very simple, very nicely done.

The other slightly arcane point in the manual is the matter of the damper rod nut/adjuster gap on page 5-39. At issue is the same problem as the old fork had when the teach would fail to back of the rebound clickers. What is supposed to happen is for the damper rod to screw all the way into the adjuster and bottom out in it. This gives the adjuster a consistent and repeatable distance between it and the actual damper valve in the cartridge. If the clicker is too tight, the rod will screw in until the push rod bottoms on the clicker screw without running all the way in, and then, 12 clicks will be something different than what it was before. The key here is to back the clickers all the way out, run the nut all the way down the rod threads, and then run the adjuster down to bottom out (Just snugly) on the rod. After that, you can just tighten the lock nut, and not worry too much about the gap setting.

On the whole, the new fork is even simpler to work on than the old single chamber fork was. :censored:

Note that it is not necessary to disturb the seals in order to do the oil change, either.

BTW: I would recommend replacing the seals and dust sliders while

Thanks Gray! I've got a set of seals on order... mine are both seeping a little. Went with the Factory Connection seals as i have read the OEM don't seem to be holding up as well as they should. One other question, manual says to use the S1 fluid. Do you happen to know what weight oil that is so that I might have the option of using a different brand? Thanks again for all your words of wisdom!!

The S1 fluid is available at good Yamaha dealers, but is, um, expen$ive! ($27/qt). So, even though I could not get a really firm, definitive statement as to the equivalence of it, I was told that the dealer carried Maxima 3wt Shock Fluid ($10/qt) as a substitute. I used it in ours, and it seems to be fine.

Wow, 3wt??? Wasen't the 01 fluid like 5wt? Yeah, Yamaha is proud of their fork oil... thats why I always replaced mine Maxima.

Yeah, "01" is 5wt. S1 is definitely lighter. I used a very scientific test to determine that the 3wt Max and S1 are about the same: I sloshed both cans :censored:

Either way, that was the recommendation I got, weak as it was, and it worked OK.

Lol. Sounds good to me, I'll give it a try. Thanks again!

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