Fork Oil Change

[cbrxxquad]

I was trying to tell you when I get it (high speed weave) was when I have the preload backed off mine all the way. and that I have my tubes slide up farther than stock bird. You have the shim in the back and the tubes slid too don't you?

I am guessing, but, undo any of the changes, rear shim, tube location, it will go away. I think you said the sag was correct.

[Para045]

I was trying to tell you when I get it (high speed weave) was when I have the preload backed off mine all the way. and that I have my tubes slide up farther than stock bird. You have the shim in the back and the tubes slid too don't you?

I am guessing, but, undo any of the changes, rear shim, tube location, it will go away. I think you said the sag was correct.

My circumstances seem almost the opposite of yours

When I first did the fork swap I had an 8mm shim on my 900RR shock, tubes up ~3mm in the triples (front lower), heavier springs with ~21.5mm preload, 5w oil at 154mm.

I first removed the 2mm back to a 6mm shim - helped a bit, then moved tubes lower (triples up) and loosened the headstem bearings a smidgen - helped a little bit, then dropped preload to ~9.5mm (like stock) - helped some more but it's still there

Not sure whether to cut the spacers more (which will possibly throw out my sag) or put some more oil in as they are 04 forks and are supposed to be at 142mm not 154mm

Static sag is in the correct range from several sources

[cbrxxquad]

I was thinking, and I might be wrong, that the rake of the bike caused the weave.

To clarify what the rake is. If the angle of the forks is to steep. What evilxx was saying where the fork angle is to small. When you get the rear high and the front low the fork angle gets below 25 deg.

In the car world, it is called caster. On my quad, if the caster is below 6 deg, I loose high speed stability but it turns slow real easy. It is called scrub because the tire will loose resistance in turning the tire. In bikes it is trail. if you follow the forks to the floor the point it hits is ahead of the contact patch of the tire. Ie trails behind the angle of projection. The less trail the less stable. Pure sport and race bikes have less than touring for sure and need dampeners to prevent the weaving. Now that is how I understand it. When I backed off the preload and got weaveing i was changing the trail by lowering the front, which is already low compaired to stock birds. But I am prety sure the zx trees are also steeper than the bird, also reducing the angle.

What I am wondering, is if you take out the 6mm shim will it go away. I know that the rear shim is very much more effective than the front changes at changing the angle of the forks,,ie trail.

Have you checked tire pressure? Don't you have a aftermarket shock on the rear?

[Para045]

What I am wondering, is if you take out the 6mm shim will it go away. I know that the rear shim is very much more effective than the front changes at changing the angle of the forks,,ie trail.

Have you checked tire pressure? Don't you have a aftermarket shock on the rear?

I have a 95 CBR 900RR shock with a 1100lb Eibach spring on the rear + the 6mm shim, I guess I could try taking that out as well and see what it does

Just don't want to lose the extra "turn in" it offered but at least it would tell me what direction to go in

Thinking about it though I have actually "lifted" the front up on the bike with the heavier springs so shouldn't that be making the trail longer and therefore the bike "more" stable

It definitely is higher as my HID's are blinding everyone on the road because they are pointing high now

Checked the pressures and all OK, ~41psi cold

[ActionStarCBRxx]

Awesome write up Hobie!

I finally pulled my forks yesterday. I have the oil drained and I will be putting in new springs from Race Tech. I bought fork seals and the tool from Racetech to press the seals back in place... but I am tempted to not replace them... as I dont have a leak in either seal.

Whats the general consenses on replacing fork seals? Changing as part of maintenance or what till they leak and then replace them?

Also... the little allen bolt at the bottom... I can't get that bolt out. Should I just ignore it? I pumped the forks several times to get the oil out and I left the forks turned upside down over night to let the rest of the oil drain out. Is there more goob thats at the bottom that wont be sucked through when pumping the cartridge?

Let me know your thoughts!

Thanks!

K

[Hobicus]

Awesome write up Hobie!

I finally pulled my forks yesterday. I have the oil drained and I will be putting in new springs from Race Tech. I bought fork seals and the tool from Racetech to press the seals back in place... but I am tempted to not replace them... as I dont have a leak in either seal.

Whats the general consenses on replacing fork seals? Changing as part of maintenance or what till they leak and then replace them?

Also... the little allen bolt at the bottom... I can't get that bolt out. Should I just ignore it? I pumped the forks several times to get the oil out and I left the forks turned upside down over night to let the rest of the oil drain out. Is there more goob thats at the bottom that wont be sucked through when pumping the cartridge?

Let me know your thoughts!

Thanks!

K

I don't traditionally replace seals unless they are leaking. At 72,000 miles.. no leaks yet. I DO clean the fork tubes right afer I pull them (with Honda Polish, or the Not Honda Polish equivalent) so that they don't let any dirt get under the seals.

If you can't get the bolt out, don't sweat it. Just pump the rod inside until it's clean, and see some of the above suggestions for rinsing/cleaning to get the rest of the dirty oil out of the tube. I believe some people use a little Kerosene, and some just flush it with clean fork oil a couple times.

[Para045]

I believe some people use a little Kerosene, and some just flush it with clean fork oil a couple times.

Yeah thats all I did when I recently replaced my forks with some used 04 ones

I hung them upside down overnight to drain most of the old oil out while pumping them every so often in the first 1/2 hr.

Then I poured in some Kero pumped the damper rod and the tube up and down about 20 times and hung upside to drain again for 1/2 a day then did the kero again and hung overnight and that got most of the shitty old fluid and grit out :icon_think:

[Hobicus]

I believe some people use a little Kerosene, and some just flush it with clean fork oil a couple times.

Yeah thats all I did when I recently replaced my forks with some used 04 ones

I hung them upside down overnight to drain most of the old oil out while pumping them every so often in the first 1/2 hr.

Then I poured in some Kero pumped the damper rod and the tube up and down about 20 times and hung upside to drain again for 1/2 a day then did the kero again and hung overnight and that got most of the shitty old fluid and grit out :icon_think:

Only part of that process (Aside from being totally anal about it) is that it takes days to complete.

My take on it is that you're better off buying a cheap brand of fork oil (or go nuts and buy the Honda stuff) and use it as a flush, and be able to go riding that afternoon than miss a day of riding, waiting on your forks to drain.

[Para045]

Only part of that process (Aside from being totally anal about it) is that it takes days to complete.

I had other stuff to do like the SH Bearings and getting some new tyres fitted to the rims anyway so the extra time was nothing espescially as I work shiftwork and get limited time to do stuff sometimes anyway

That and even a "cheap" fork oil over here is something like Motul and $36L

So kero is much cheaper

[Zero Knievel]

QUESTIONS:

1. What is bad about draining oil out bottom of fork as provided by engineers?

2. Since you have to pump the fork to get the air out anyhow, why not drain thoroughly then add the specified amount of oil and pump. Should that not get the desired result compared to overfilling?

[Hobicus]

QUESTIONS:

1. What is bad about draining oil out bottom of fork as provided by engineers?

2. Since you have to pump the fork to get the air out anyhow, why not drain thoroughly then add the specified amount of oil and pump. Should that not get the desired result compared to overfilling?

There is no "drain plug" with the exception of pulling the cartridge. When you remove the cartidge, you can get all the oil out, as well as all the goop that builds up in there over time.

Adding the specified amount of oil does not guarantee that you'll get the proper air gap. The service manual specifies an amount of oil to add, but then specifies that you check the air gap anyways. As long as you add enough to keep the cartridges from sucking air, you're going to have to top it off anyways after pumping the cartridges to distribute the oil. Not measuring when filling saves a step, and requires less tools. If you end up with an air gap that's over the specified amount after measuring the oil, you still have to remove the excess oil.

[Zero Knievel]

QUESTIONS:

1. What is bad about draining oil out bottom of fork as provided by engineers?

2. Since you have to pump the fork to get the air out anyhow, why not drain thoroughly then add the specified amount of oil and pump. Should that not get the desired result compared to overfilling?

There is no "drain plug" with the exception of pulling the cartridge. When you remove the cartidge, you can get all the oil out, as well as all the goop that builds up in there over time.

Adding the specified amount of oil does not guarantee that you'll get the proper air gap. The service manual specifies an amount of oil to add, but then specifies that you check the air gap anyways. As long as you add enough to keep the cartridges from sucking air, you're going to have to top it off anyways after pumping the cartridges to distribute the oil. Not measuring when filling saves a step, and requires less tools. If you end up with an air gap that's over the specified amount after measuring the oil, you still have to remove the excess oil.

Does leaving the "goop" in there lead to problems down the road?

[Hobicus]

Does leaving the "goop" in there lead to problems down the road?

The main cause of leaky seals is dirt in the oil or on the fork rubbing against the rubber seal, acting like sandpaper and causing it to leak. If you don't get the goop out at the bottom of the fork, it will just hasten the demise of the seals.

[Zero Knievel]

Does leaving the "goop" in there lead to problems down the road?

The main cause of leaky seals is dirt in the oil or on the fork rubbing against the rubber seal, acting like sandpaper and causing it to leak. If you don't get the goop out at the bottom of the fork, it will just hasten the demise of the seals.

Ah, I see. Re-reading I see part of the process is to clean out the entire fork and all parts, so all the "goop" will be removed.

[squag1]

I was a lazy &(&*^% I did it with the forks in.

I opened the bottom bolt and it went back ok.

I let it drain for a day and flushed oil through it as well.

Centering the forks is the only difficult bit.

I had tightened up too many things before I aligned it.

Made a big difference with new oil.

[Zero Knievel]

If I missed it, I apologize, but what brand and weight of oil for the forks is recommended? How much should I get to do the job?

[Redbird]

Stock is 10w, you should need about a liter, IIRC.

[Zero Knievel]

Is there a difference in using 5w vs. 10w?

[Redbird]

Yeah, less damping.

[jon haney]

If you are a heavier guy and are planning on doing some track days, I would stick with the 10W.

If you want a cushy riding tourer, go with 5W.

Go with 7.5W (if you can find it) or mix the two above, if you want something in between.

[Zero Knievel]

From another board while looking for information...an interesting FYI on springs and oil viscosities.

This is a very general guideline for fork oil weights. One thing you need to remember is that, like all fluids, fork oil viscosity is reduced as the oil temperature increases... so, under racing conditions, the oil will heat up and thin out more. On the street, it will stay relatively constant. This is one reason race shocks (and superbike forks) have reservoirs to help cool the oil. They also provide a space for nitrogen to pressurize the fluid. This helps keep foaming and cavitation (air bubbles) through the valve to a minimum.

100-150lb rider with .85-.90 spring = 5 wt

150-180lb rider with .95 springs = 7.5wt

180-215lb rider with 1.0 spring = 7.5-10 wt

215-240lb rider with 1.05 spring = 10-12.5 wt

240lb and above with 1.10 spring = 12.5-15 wt

There will be some overlap in these numbers based on usage but that's about how they stack up.... BTW.. to make the half weights (I.E. 7.5 wt = 1/2 volume of 5 wt mixed with 1/2 volume of 10 wt)

Now for the disclaimer! Different fork manufacturers use different "port sizes" in their valve assemblies (requiring different viscosity) so this is not "chiseled in stone" Please verify all your oil wt questions via a manufacturer's representative!

- From http://www.speedzilla.com/forums/rc51-tech...t-fork-oil.html

[Redbird]

The last statement there is the only one you should pay attention to. It's impossible to state rules of thumb like that across all makes and model. Too many variations in stock valving and OEM oil viscosity.

[HANKSXXX]

The last statement there is the only one you should pay attention to. It's impossible to state rules of thumb like that across all makes and model. Too many variations in stock valving and OEM oil viscosity.

The air column, governed by fluid level, can also be "tuned."

My feeling is that the manufacturers recommendation is a starting point.

Sag settings fall into the same category.

The more I dabble with this stuff, the more I appreciate the speciality suspension shops.

[Redbird]

The more I dabble with this stuff, the more I appreciate the speciality suspension shops.

Amen. I read all the books, took a four hour freakin' seminar with an pro AMA suspension tuner, spent days at the track tweaking this and that and trying to note changes....then I spent $80 to have a guy set me up trackside and realized I was wasting my time. If you're going to spend money on hard parts, drop a little extra to have a pro set it up.

In the case of this thread that probably doesn't apply, though. As you said, OEM spec is a place to start. Springs, sag, tune damping via oil weight and air gap...good enough for the street.

[BASTOK]

In the last 3 month I tried different fork oil viscosities.

1- 10w stock one (after reading lots of posts I decide to try others to look how they feel)

2 - 15w........ too harsh, steady but really harsh. It would be only recommended for a totally smooth road surface. A little bump feels like hell

3 - 7.5..... less damping, you notice that inmediately. I'm 98kg and I felt the bike too soft, i like to feel the road, it gives me safe feeling.

4 - 10w.... return to the stock and I'm happy with it again (but as I tried all the others, I have no doubts!!!)

I have 1.0 racetech springs, and sag set at 3cm front