2005 YZ250 Forks AOSS Rebuild

[Satch0922]

I posted this here because most of the AOSS forks are on the 05 YZ's. I just did a third rebuild on the forks. The forks have been revalved but had become a mess! This is what I learned after doing the rebuild. Some of it you already know .....some you may not.

1. The AOSS forks are a bear to bleed and purge the air out of them. There is s a method that works....but you must be patient and if you "think" you messed up....do it again. Here is the method that works:

"I have had luck with bleeding the inner chamber of the Kayaba fork by filling and bleeding the cartridge and piston rod, then installing the base valve ***'y (with the pre-load increased) just deep enough to squirt oil out of the side holes. Then I put the whole cartridge in a vise at about a 60 degree angle with the hole in the cartridge tank up. I push against the base valve while compressing the piston rod slowly.
There will be a "farting" sound as the air trapped beneath the free piston cavity escapes because of the angle the cartridge is at. I slowly stroke the piston rod up and down a few times until I compress it to a little before full stroke. Then I extend the rod and screw in the base valve. When done properly, this is the best way I've found to bleed the air out and have a fully extended rod after bleeding it and charging the rod full stroke...}"

2. These forks demand maintanence. I am convinced that air (maybe air bubbles trapped in the oil?) builds up in the inner chamber or perhaps the oil in the inner chamber just breaks down fast. I am no expert but I can tell you that an oil change does wonders for these forks....I think the interval at which they are changed is more critical than the "old" style KYB forks.

3. I experimented with Mobil 1 Synthetic Trans Fluid in the forks. BigM told me that this was the new thing and you guys know me......I had to try it. I am happy to say that it works GREAT! After the rebuild I set all the clickers to the stock settings so I could dial it in. I knew it would be different with differnt fluid. All I can say is the Mobil 1 SATF allowed me to back out on the compression giving a plush feel (plush for me ) and I had to go stiffer by two clicks on the rebound. Bottom line....I LIKE THIS FLUID!

4. The only other change was to add preload spacers on the base valve. This increases the preload and helps keep the forks from blowing through the stroke as fast. I felt the bike was more stable and also helps the forks feel more plush (as they are not hanging as far down in the stroke). It had no adverse affects on corning.

Sorry for the long winded post. The 05 forks can be made to be pretty good. Yeah their not the 06 SSS forks but they are pretty darn good.

[*cly.sp*]

Very informative post. makes me feel like I've been neglecting the forks on my 05...they have about 45 hours on them and they havent really been touched except for the ari-bleed screw an seal savers.
One thing I have found that works very well is pulling the dust seal down and cleaning the area inside the fork.. then sticking a .005 mm shim up through seal and bleeding a little oil down along with any dirt that got up there. I read this DB awhile back and whenever it seems like forks were getting alittle harsh or felt more vibraty this seems to help IMO.