Another Fork ?

[mmbasa]

With all this suspension talk, got me thinking I should service my forks. On the twin chambers (07 450) if you replace the fluid in the outer chamber should you also do the inner?

[grayracer513]

You would not strictly have to, since the inner cartridge is a sealed assembly and draws no oil from the outer chamber, but my feeling is that unless you are using the same fluid as was originally installed, it's a good idea to do it the first time, at least. After that, say if you had a seal go out in less time than you thought would require a complete oil change, you could just replace the seal and the outer oil, and you would know that it matches up.

It really is an easy fork to work on once you've done one, and could have been much more complicated and difficult to do if they hadn't spent so much effort on setting it up the way it is.

[mmbasa]

Do you need to take the tubes apart to change the fluid in both chambers? And for the inner chamber, do you measure the height or just a certain volume and bleed till nothing else comes out?

[grayracer513]

The outer chamber is filled to a specified volume in ounces or CC's. The fork is fairly sensitive to changes in this level, and variations as small as 5cc per side are said to be noticeable. It would affect the "air spring" behavior of the trapped air within the fork, just as with the older models.

The inner chamber is set up so that you first bleed air from the internal valving by working it through some, then fill to a set level, compress the damper completely, then push the base valve into place while allowing the damper to extend as the valve is inserted and screwed down. This, when done right, and it's easy to do right, automatically excludes any air from the cartridge. So, the answer is that the inner is completely filled.

The outer chamber oil could be changed or added to or subtracted from on the bike by unscrewing the cartridge assemblies from the top, then removing the rebound adjuster from the bottom to drain, if desired.

In fact, the cartridges could be dismantled from the forks and the fluid in them changed as well, without ever removing the front wheel, if you were so inclined.

[mkporn]

The outer chamber is filled to a specified volume in ounces or CC's. The fork is fairly sensitive to changes in this level, and variations as small as 5cc per side are said to be noticeable. It would affect the "air spring" behavior of the trapped air within the fork, just as with the older models.

The inner chamber is set up so that you first bleed air from the internal valving by working it through some, then fill to a set level, compress the damper completely, then push the base valve into place while allowing the damper to extend as the valve is inserted and screwed down. This, when done right, and it's easy to do right, automatically excludes any air from the cartridge. So, the answer is that the inner is completely filled.

The outer chamber oil could be changed or added to or subtracted from on the bike by unscrewing the cartridge assemblies from the top, then removing the rebound adjuster from the bottom to drain, if desired.

In fact, the cartridges could be dismantled from the forks and the fluid in them changed as well, without ever removing the front wheel, if you were so inclined.

Help a guy out understanding this for a second. I thought you filled the inner to a a level, installed the cart with the rod extended then compress the rod and drain blow of oil? The rod should return to full extended position.

Point me in the right direction.... Not as familiar with the yamaha twins as the Honda's.

[mmbasa]

So from what I understand, I don't need to separate the tubes. But in order to remove the cart I have to unscrew it from the bottom of the fork?

[grayracer513]

That's correct. The cartridge assembly screws in at the top of the upper tube (takes the place of the fork cap) and at the bottom of the lower tube, where the base valve once was. In order to get the cartridge separated from the outer tube assembly, you need to remove the rebound adjuster from the damper rod, just as you would remove the fork cap from the rod on the old single chamber fork.

[mmbasa]

And then replace with a 5wt?

[grayracer513]

3wt

https://www.thumpertalk.com/forum/showthread.php?p=4397949#post4397949

[red7]

Do the seals need to be replaced every time?

[mmbasa]

How about 2.5, or is that to light?

[grayracer513]

I don't really know if that's too light or not, because I don't yet have a definitive answer to what exactly Yamaha's "S1" fluid is. 2.5's not far from 3 wt, so it might work.

[mmbasa]

Just trying to get my head around all this, I really want to change the fluids myself, but want to do it right without messing anything up.

Should I buy one liter or two?

What is the stock volume in the outer chamber?

I'm a little confused on the manual. On 5-33 thru 5-35 for the damper assembly, it says to fill then pump. Is that with the cap off? Then it says to measure the height. I thought it was by volume. Book calls for 6.59 oz.

Then it says "First bring the damper rod pressure to a maximum. Then install the base valve while releasing the damper rod pressure." What does that mean?

[grayracer513]

You'll need two quarts, as the job takes about 36-38 ounces to do.

On page 5-40, it lists 355cc (12 oz) as the oil amount for the outer.

The damper is first filled to the specified level and then pumped several times (at a moderate rate; not too fast) through its full stroke to purge air from within the damper. And yes, that is with the cap off.

I'm glad to hear that the very oddly worded note to which you refer confused you. It means you're normal. What they were trying to say was this:

"Fully compress the damper rod. Then insert and screw down the base valve while allowing the rod to extend as the valve is installed." If this is done right, the damper rod should be fully extended once the valve is screwed all the way down. If you have to pull the rod out a little to get it to be fully extended, take the valve out, add 2-3 ounces of oil and try again.

After you get the valve in place, you next need to force the damper to fully compress a couple of times to force out any excess oil, which you will then pour off out of two small holes in the side of the unit.

Pretty easy job, really.

[mmbasa]

So 355cc is the stock oil volume per side?

So push down, screw the cap on then release and it will fully extend itself?

[grayracer513]

So 355cc is the stock oil volume per side?

That's the outer chamber volume per side, yes. The oil in the inners is not included in that amount

So push down, screw the cap on then release and it will fully extend itself?

Not quite. Once filled and the air worked out, push the rod all the way up, or in, or compressed. Say you're holding the cartridge in your left hand, and it's sitting on the bench with the rod pushed in all the way. Pick up the base valve in your right hand, pick the cartridge up off the bench so the rod is no longer held up by anything, and insert the base valve. The rod will extend as this happens.