A few words on fork oil level

[LeftCoastAdv]

Hello all,

I just installed a set of intiminators and browsed this sub-forum to get any insight before I did. I already have pretty deep knowledge about suspension, but you never know, there may be a hard learned lesson or two that I could benefit from. Thanks to all who asked good questions and those that answered them and contributed to the fantastic knowledge base here.

One thing that seems to come up over and over, and there seems to be a bit of confusion and bad advice given about, is fork oil level.
I offer a cursory view of why fork oil level is important and how it affects how the forks work.

I have an '08 and matching kawi shop manual, so I'll reference that.
The manual calls for an oil level of 135mm below the top, spring, washer and spacer removed with a tolerance of +/- 2mm. +/- 2 mm is not a lot at all, so that should tell you that oil level is a very precise and very important measurement, not something to be done sloppily or taken lightly. 2mm is less than 1/10 of an inch. Pretty exact.

The shop manual does say that the fork takes approximately 500ml, but that is no doubt in there to let you know how much to have on hand before you start your service. You CAN NOT fill your forks by measuring the quantity of oil that you put in. You HAVE TO measure from the top. Why? Maybe you didn't get all of the oil out of one or both legs when you drained it. Also, the important measurement is not the quantity of oil, but rather the size of the air space between the top of the oil and the cap on the top of the fork leg (more on this below).
Also, you can not measure how much oil came out and just replace that amount. By way of example, my left fork had about 100ml LESS oil than my right leg did, and neither was close to 135mm from the top. Chalk one up to the QC at the factory. Same guy that greases the swingarm bearings probably fills the forks too. No wonder the forks were so squishy stock, and constantly bottomed out. This is on a 1 year old, 3500 mile bike.

Doing the Intiminator install, after you've purged all of the old oil out and let them drain for a while, I suggest that you pour a little fresh 5wt oil in there to rinse them. You'll have plenty of extra oil- 1 bottle is not quite enough for both legs, so you had to buy 2 bottles, leaving you with almost a full bottle extra. Pour in ~200ml or so and pump the leg a few times to rinse the metal dust out. Pump and drain them again, you'll be amazed at how much powdered metal comes out, plus it will flush out the remaining thicker stock oil from the factory.

Then, pour about 400ml of oil in the leg and pump it to release trapped air from the damping circuit. Let it sit for a few minutes for any bubbles to rise to the surface, then put the Intiminator in. You have to use the spring and spacer to push it through the oil to the bottom, then hold it there and pump the fork a few more times to release any air that got trapped under it.
Remove the spring and spacer, compress the fork all the way to the bottom, THEN measure 135mm from the top and add oil as needed.

I've seen suggestions in this sub-forum to measure the oil level BEFORE you put the Intiminator in. This is incorrect. The shop manual calls for the oil level to be set with the spring, washer and spacer removed. The intiminator cartridge will of course displace oil when it goes in, so if you measure 135 THEN add it, your oil level will be way too high- 30 or 40mm I would guess. Again, with a tolerance of +/- 2mm, this would put you way, way out of spec.

The reason that it's important to measure the air space above the oil is this.
All forks are by design, "progressive". They have 2 springs- one is the metal coil spring, and the other is that air space trapped above the oil, below the cap, that gets "stiffer" the more you compress it. As the fork compresses, the oil level rises in the tube, compressing that air space (gasses compress, liquids do not).
That air spring gets very firm just before the fork bottoms out, which is what keeps it from bottoming out.

No doubt very complex calculations were done by very smart Japanese engineers to determine exactly how much oil needs to be in there to give the correct volume air spring that will compress just enough to prevent bottoming out, but not give a harsh ride at the bottom of the travel. I trust them.

Hope someone can find this info useful.

[hillbilly_KLR]

Great post LCA! I concur. Well written and easily understood.

Ain't the Intiminators great...

[fixer]

Originally Posted by LeftCoastAdv

The shop manual calls for the oil level to be set with the spring, washer and spacer removed. The intiminator cartridge will of course displace oil when it goes in, so if you measure 135 THEN add it, your oil level will be way too high- 30 or 40mm I would guess.

the Intiminators will displace oil... but just guessing from the volume of the cartridges, i'd guess it will displace less than half the oil that you're guessing it will. simple enough to check, but i don't feel like popping the cap on my forks right now.

and IIRC, when they installed the Intiminators in my '00 at the Ricor shop, i seem to recall them measuring the level BEFORE they dropped them in. but it's been a while, i could be misremembering. IIRC they set the airspace at 170mm, and IIRC the OEM spec is for 190. many people without the Intiminators regularly run the oil at 150mm

no coffee yet and i didn't get any sleep last night, so i could very well be misrembering any of those numbers.

bottom line. make the oil on both sides level, and more air will be softer, less air will be firmer. that works with stock forks or with Intiminators (or any other cartridge)

[psdeavers]

The instructions that come with the Intiminators :



Intiminators go in BEFORE setting the oil height

Pre-'08 bikes are 190mm from top and '08-up bikes are 135mm from top.
I set my height at 170mm from top on my '04, works great for me.

[LeftCoastAdv]

Originally Posted by fixer

no coffee yet and i didn't get any sleep last night, so i could very well be misrembering any of those numbers.

Then, with all due respect, why did you post? My post was intended to clear some very muddy water. Posts like yours with guesses, "IIRC" and misinformation are the reason that people get confused and have trouble with their installations.

Have your and go re-read the third paragraph of my post. I referenced the '08 installation, which calls for 135mm of air space.
You have an older bike than that, so your numbers may be correct as well, but have no bearing on what I've written.
Certainly, most people reading this are intelligent enough to find out the proper oil level for their forks, and substitute that number (and by "find out", I mean go and look at a factory shop manual, don't rely on the "IIRC" crowd to guess for you).

The entire point of my post, is that oil level is very important, not a loosey-goosey guess as you've implied. People very familiar with suspension, with experience tuning suspension should play with their oil level. Those people already know everything that I've written, so my post was not targeted at them.
Those who are doing this kind of work for the first time, perhaps confused as to why their forks aren't working as they should after the install would do well to do it by the book. That, and that alone was my point.

This is from the instructions included with the Intiminators, which you probably would have read had you done the install yourself:

5. Hold the fork vertical and add fork oil... Cycle the fork slowly without the Intiminator installed to bleed any air.
6. Install the intiminators and set the oil height.
7. Install the fork spring, washer and spacer.

psdeavers' scan of a different part of the install sheet states this as well (thanks for that scan and post!)

Unless you or others have useful additions or corrections to what I've written, I'd like to keep this thread clear and easy to read and understand.

Thanks in advance.

[Padmei]

Thanks for this post LCA. I am having a coffee, about to do my new intimators. Now I know what to look out for.

[Mark_S]

Originally Posted by Padmei

Thanks for this post LCA. I am having a coffee, about to do my new intimators. Now I know what to look out for.

well get off your fat lazy bum and get to work

ask Igor to help

[Padmei]

Originally Posted by Mark_S

well get off your fat lazy bum and get to work

ask Igor to help

Check out my intimators experimental testing results coming to a thread near you

[grtfshrmn]

I noticed you mentioned you have deep knowledge on suspension. I have a couple of questions hoping you can help.

My 2008 KLR 650 feels really top heavy or turns like a chopper. Is there some adjustments or specs I should check to make the slow tight turns easier and not feel like I am going to drop it. I have dropped it several times in the dirt trying to make turns. Had another guy that is very experienced try it and he almost went over.
Thanks in advance.

Originally Posted by LeftCoastAdv

Hello all,

I just installed a set of intiminators and browsed this sub-forum to get any insight before I did. I already have pretty deep knowledge about suspension, but you never know, there may be a hard learned lesson or two that I could benefit from. Thanks to all who asked good questions and those that answered them and contributed to the fantastic knowledge base here.

One thing that seems to come up over and over, and there seems to be a bit of confusion and bad advice given about, is fork oil level.
I offer a cursory view of why fork oil level is important and how it affects how the forks work.

I have an '08 and matching kawi shop manual, so I'll reference that.
The manual calls for an oil level of 135mm below the top, spring, washer and spacer removed with a tolerance of +/- 2mm. +/- 2 mm is not a lot at all, so that should tell you that oil level is a very precise and very important measurement, not something to be done sloppily or taken lightly. 2mm is less than 1/10 of an inch. Pretty exact.

The shop manual does say that the fork takes approximately 500ml, but that is no doubt in there to let you know how much to have on hand before you start your service. You CAN NOT fill your forks by measuring the quantity of oil that you put in. You HAVE TO measure from the top. Why? Maybe you didn't get all of the oil out of one or both legs when you drained it. Also, the important measurement is not the quantity of oil, but rather the size of the air space between the top of the oil and the cap on the top of the fork leg (more on this below).
Also, you can not measure how much oil came out and just replace that amount. By way of example, my left fork had about 100ml LESS oil than my right leg did, and neither was close to 135mm from the top. Chalk one up to the QC at the factory. Same guy that greases the swingarm bearings probably fills the forks too. No wonder the forks were so squishy stock, and constantly bottomed out. This is on a 1 year old, 3500 mile bike.

Doing the Intiminator install, after you've purged all of the old oil out and let them drain for a while, I suggest that you pour a little fresh 5wt oil in there to rinse them. You'll have plenty of extra oil- 1 bottle is not quite enough for both legs, so you had to buy 2 bottles, leaving you with almost a full bottle extra. Pour in ~200ml or so and pump the leg a few times to rinse the metal dust out. Pump and drain them again, you'll be amazed at how much powdered metal comes out, plus it will flush out the remaining thicker stock oil from the factory.

Then, pour about 400ml of oil in the leg and pump it to release trapped air from the damping circuit. Let it sit for a few minutes for any bubbles to rise to the surface, then put the Intiminator in. You have to use the spring and spacer to push it through the oil to the bottom, then hold it there and pump the fork a few more times to release any air that got trapped under it.
Remove the spring and spacer, compress the fork all the way to the bottom, THEN measure 135mm from the top and add oil as needed.

I've seen suggestions in this sub-forum to measure the oil level BEFORE you put the Intiminator in. This is incorrect. The shop manual calls for the oil level to be set with the spring, washer and spacer removed. The intiminator cartridge will of course displace oil when it goes in, so if you measure 135 THEN add it, your oil level will be way too high- 30 or 40mm I would guess. Again, with a tolerance of +/- 2mm, this would put you way, way out of spec.

The reason that it's important to measure the air space above the oil is this.
All forks are by design, "progressive". They have 2 springs- one is the metal coil spring, and the other is that air space trapped above the oil, below the cap, that gets "stiffer" the more you compress it. As the fork compresses, the oil level rises in the tube, compressing that air space (gasses compress, liquids do not).
That air spring gets very firm just before the fork bottoms out, which is what keeps it from bottoming out.

No doubt very complex calculations were done by very smart Japanese engineers to determine exactly how much oil needs to be in there to give the correct volume air spring that will compress just enough to prevent bottoming out, but not give a harsh ride at the bottom of the travel. I trust them.

Hope someone can find this info useful.

[LeftCoastAdv]

Originally Posted by grtfshrmn

My 2008 KLR 650 feels really top heavy or turns like a chopper. Is there some adjustments or specs I should check to make the slow tight turns easier and not feel like I am going to drop it. I have dropped it several times in the dirt trying to make turns. Had another guy that is very experienced try it and he almost went over.
Thanks in advance.

Hi Wayne,
Good question. There are probably a couple of suspension and set-up related things you could do, but I wouldn't recommend doing any of them. Suspension and set-up are always compromises. If you make the bike handle better at extreme low speeds, it'll probably make it handle terribly at speed. Unless you spend a majority of time poking along, I'd leave it alone.

I know exactly what you're talking about regarding the slow speed handling. I think there are 3 things that cause it (at least).
One, is that the bike is very heavy.
Second, is that that weight is mostly up really high. With a 6 gallon gas tank and you sitting up on the tall bike, it's very top heavy.
Third, is that the suspension, especially up front, is really soft and mushy.


Instinctively when we ride slowly and turn, or go over bumps or rocks, etc, the weight of the bike is pushed off balance, and we make adjustments consciously or unconsciously to shift that balance back to center. You move your hips, your shoulders, your knees, your head, elbows, whatever, back and forth to re-establish balance. Push or pull on each side of the handlebar. In addition, you sometimes gently blip the throttle to momentarily make the front a little lighter, or cut the throttle or use the rear brake to make the front heavier and you do all that stuff simultaneously. The more experienced you get the less you're aware of it, it just happens.
The problem is that with those mushy forks, most of that effort just gets absorbed and not transferred to the bike, so you push a little harder or shift your weight a little more and all of a sudden the suspension loads up, pushes back and really throws you off balance.
An obvious fix would be to put stiffer springs up front so the bike is stiffer and more predictable, but again, that'll have the unintentional effect of changing the handling a lot at all speeds, maybe not for the better. I think this is the reason the intiminators (to keep it on topic...) are so popular. They add a lot of damping to the hydraulic circuit and give the impression that the forks are stiffer, but when you go faster and hit a bump, they release and you get your plush ride back just when you need it. Cartridge emulators kind of do the same thing. Have you installed anything like that?
One thing I can recommend, technique-wise, is that when you ride slowly or over uneven ground, stand up on the pegs on the balls of your feet, knees slightly bent. When you are sitting down on the seat, your mass and the bike's mass become one, and you compound the top-heavyness of the bike. If you're up off the seat, your weight and the bike's weight can go in different directions, and it makes it very easy to make radical weighting changes to make up for bumps or lost traction, etc.

I appreciate that your experienced friend had troubles with the balance of the bike as well, but it could just be that he's not used to your bike, and it's weighting, or more likely, that his brain and muscles have memorized the characteristics of his bike, so when he subconsciously tried to apply that to your bike, it didn't work.

My best recommendations are to think about doing something to stiffen up the front end (that won't sacrifice high speed handling, like Intiminators or cartridge emulators), but more importantly, just practice riding your bike slowly a lot, to train your brain and muscles how to react when they need to.
A lot of it is having the strength in your torso, hips and arms to be able to muscle that bike back and forth when you need to, and that also only comes with practice and riding a lot.
I'll sometimes go months without riding the KLR, just because I'm busy riding other bikes, or it's over 100 degrees every day in the summer and too damned hot to ride, etc, and before I use it to go on a trip or a ride in the back country, I always do at least 30 minutes of slow riding, making turns, going over curbs and rocks, etc just to re-train myself about it's handling and wake those muscles back up.

Have you ever seen guys on racing bicycles at stop lights doing "track stands", where they're stopped but rocking the bike forwards and backwards gently to maintain balance, or if they're really good, just stopped there perfectly still waiting for the light to change? They do it so they don't have to unclip their shoes from their pedals. That's the extreme example of what I'm talking about. Complete control over their weight and the bike's weight and the ability to make constant micro-changes to maintain balance. That only comes with a lot of practice.

Hope it helped-

[Padmei]

Another great reply LCA.
I have been riding my 08 for just over a year & for a while dropped it on nearly every ride (off road of course). I found that as soon as it was a little off balance - timmmmmber...
I suspected the same reasons that LCA stated.


I began trying a few things such as only 1/2 filling the tank for shorter rides or when I knew there would be gas after a technical section. Also worked on my abs as I always seemed to hurt my back trying to muscle back up to the balance point. The best thing was watching the Dualsport technique DVD & practising their handling skills & drills.
Nowadays I can go out riding & really lean the bike over sideways without it falling over simply by 'knowing' what it's likely to do & counteracting with body positioning.
Where I once was getting really frustrated with it, I now am more in tune with it & have a lot more fun & a lot less painkillers.

[Hamilton.Cooper]

+1 to everything from LCA!

Ricor suspension was worth every penny and the wait. Check out my posts about the incarnations of my bike.

Also a 14t front sprocket goes a LONG way off road!

[lashl]

The intiminator instructions say to fill the fork when it is vertical. What level would you set it to when it is still on the bike? Also do you measure from the rear of the fork top (where it would be higher than if you measured from the front) or what?? My KLR is a 2003 and thanks for any help.

[hoyks]

Originally Posted by lashl

The intiminator instructions say to fill the fork when it is vertical. What level would you set it to when it is still on the bike? Also do you measure from the rear of the fork top (where it would be higher than if you measured from the front) or what?? My KLR is a 2003 and thanks for any help.

It is because of that inaccuracy that you fill the fork standing up. You have to have it out of the bike in order to drain the oil, well on the 08+ anyway, so may as well fill it at the same time?

The critical thing is that the level in both forks is the same or it can lead to differing fork action from left to right, so if you could draw the oil out from the same point on each fork it would reduce inaccuracy.

One way would be a turkey baster with a zip-tie around it or a 20ml syringe and a short tube on the end cut to length. Over fill the forks and then suck it down to as close to the stated level as you can.

[Hamilton.Cooper]

Sorry to be the bearer of logic/bad news, but you will have to take them off the bike to measure them properly. If you are hell bent on measuring them on the bike, then make them vertical somehow. Any info you get on the measurement levels otherwise will just be hearsay.

Originally Posted by lashl

The intiminator instructions say to fill the fork when it is vertical. What level would you set it to when it is still on the bike? Also do you measure from the rear of the fork top (where it would be higher than if you measured from the front) or what?? My KLR is a 2003 and thanks for any help.

[lashl]

looks like this will be a winter project.

[Elitelf]

Too cheap to buy more than a L of the stuff, I ended up with 190mm. Still works great, but I'm only 160 pounds. I swear I'll get it up to 135mm when I get a chance.

[Bokrijder]

Everyone should keep in mind that fork fluid level is not an absolute number. It is one of the variables available in tuning a leg set to an individuals weight and riding style/ability.

Bokrijder

[Blackheart]

Originally Posted by Hamilton.Cooper

Sorry to be the bearer of logic/bad news, but you will have to take them off the bike to measure them properly. If you are hell bent on measuring them on the bike, then make them vertical somehow. Any info you get on the measurement levels otherwise will just be hearsay.

OR, you could fashion a spacer that keeps the fill/suction line in the center of the fork tube, because the fluid level at the center of the tube of a nearly verticle fork (such as when the bike is on level ground), will be equal to the level of the fluid in a verticle positioned tube. But, as previously mentioned, the level is a tuning starting point, and exactness isn't necessary.

[Gruf Rude]

Originally Posted by Blackheart

OR, you could fashion a spacer that keeps the fill/suction line in the center of the fork tube, because the fluid level at the center of the tube of a nearly verticle fork (such as when the bike is on level ground), will be equal to the level of the fluid in a verticle positioned tube. But, as previously mentioned, the level is a tuning starting point, and exactness isn't necessary.

OR you could make a simple dipstick from a 12-pack beverage box; an elongated T-shape with the dipstick 'blade' width the same as the fork's inner diameter. Mark the lengthwise center line of the blade with a ball point and put a cross at the depth of oil you are looking for.

Now all you need to do is slide the dipstick into the compressed fork, holding it perpendicular to the angle of the fork. The oil level will show up on the dipstick at an angle but the actual depth of the oil (as measured with the fork held vertically) is at the point where the oil level crosses the lengthwise center line.

For those having a hard time visualizing this, get a long tall beverage glass, fill it half full and then tilt the glass as if it were a fork tube - you will see that the actual level always remains at the half full mark at the center line of the glass, no matter the tilt.