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Fork Oil level


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OK, I had my front forks done and requested they be stiffened up a little....Now I think they are too stiff (mechanic added 20mm fluid). I am 16 clicks out on the compression dampening and I guess I'll go to 20....Is there any way to remove 5 to 10mm of fluid without redoing the entire fork??? (I have no special tools to work on the forks with)... thanks for the help.... JT

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JT1,

i just checked the manual for setting your fork oil.. you are s.o.l. (sh.. outta luck) the fork oil is measured in the fork while the fork tube and piston rod are fully compressed (like most bikes unfortunately..)and you can only do this while the cap is off...(springs have to be out as well 🙂 ) i hope this helps...

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Lay the bike on its side after removing the air bleed screw and catch the fork oil in a container. One teaspoon is about 5cc so take about 2 teaspoon out of each fork and try it out. Add oil with an eyedropper if you want to go the other way..

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All you need is a fork oil level tool and you can suck out some oil. It's important to keep the levels equal in both forks so my personal preferred method would be to go ahead and pop the caps off of the forks and use the oil level tool. Not a big job, just be sure to use your torque wrench.

The only special tools required are the oil level tool and the torque wrench. You do not have to completely disassemble the forks, just pop off the caps, remove the spring and compress the forks.

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Here's something that might help.

One (1) once of oil will change the oil height by about 11mm.

Or, 5mm of oil height is equal to about .5 (1/2) of an ounce of oil.

I can calculate precise numbers, but this is good enough for what you're doing.

Lastly, understand that oil height effects the "air-spring" in a fork. The force on the air-spring overlays the force of the metal spring.

If you remove the load of the metal spring and set the oil to the lowest height (maximum oil) it will take 165lbs of downward force to compress that one fork to bottom. If you run the highest oil level (minimum oil) the force to compress the fork without the spring is less than 1 pound.

With that, you'll get a relief on your stiffness by removing some oil, but in the real world of fine tuning your clicker(s) and stack changes should be used to control stiffness, (damping) and your oil level and spring rating should be used to set height.

That may sound a little weird or unnecessary, but if you think it through it's very important to distinguish the two.

Hope this helps.

DaveJ

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I agree with thumpalot, get yourself a fork oil level tool and do it the real way. I just added 20mm to my 450 and did it in 15min with no hurry. Once you have the tool and have done it once, you will be relieved at how much you can change your forks with so little work or cash.

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Any recommendations on the brand of fork oil level tool (motion pro??). DaveJ, I think I get what you are saying. I'm pretty sure I need to remove some fluid. I believe the stock springs (.46) are right for my weight (185-190) and I understand I need to use the compression and rebound adj. for fine tuning. I actually liked how the forks felt stock but I was bottoming on big jumps and I had set the compression all the way in. I think the shop guy just put in too much fluid now (because I cant bottom the suspension at all and the forks are stiff feeling).... Thanks again JT

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It sounds like you are trying to find the best oil level for you. Well, I think you need to start with a baseline and make sure you actually have the same amount of oil in each fork before you start tweaking or fine tuning the level in each fork. Unfortunately, you need to check the level properly, as mentioned in the previous threads (with some sort of measuring device, bought or made) and change the oil to one you think will work for you (did the service guy put the same oil as Yamaha had in there?). Then, after riding a while, you can add or subtract the amount to fine tune your ride. I used a syringe with an aquarium tube to add and subtract. To subtract, I had to loosen the top clamps and fork cap but to add, just use the air bleed hole. I used cc's and went with 2 cc increments. Squirt out the oil into a measuring container to see how much oil you removed. 6 cc can make a big difference. You can record your oil height the next time you need to tear apart your forks. Have fun.

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Thanks Sirthump and Molar. I going to get the Motion Pro and start tuning the forks myself. The shop guy added 20mm over stock to each fork (after I advised him stock was to soft). I don't know what oil he used but it sounds like the yamaha oil is the way to go. I think 10mm would of been OK but 20mm seems way to stiff. I'm mechanically inclined so I don't think this should be to hard to do.....and of course you guys got my back. Thanks again. JT

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Good move with the oil level tool. I personally use the Yamaha '01 oil and I'm very happy. Honestly I haven't tried anything else but I figured the fork was set up for this oil so I might as well keep using it (don't get sticker shock). Make sure that's what the mechanic used, I'm not sure if it's a good idea to mix oils or not.

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If you want to make a oil height tool, steal the wifes Windex bottle or any thing with a pump top and take the top off. Clean it up then measure up the tube the height you want your oil (make sure cut on bottom of tube is a 90, not cut at an angle) and make a mark. Drop the tube in your fork, your mark will flush with the top of the tube, then pump the oil out. It'll take you a few min. compared to the boughten ones but works fine.

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  • 4 weeks later...

height has to be measured with the forks compressed and the springs out. i just did mine. remove cap. remove cap from dampener rod and remove spring. (old oil should be drained) compress fork and dampener rod fully. fill fork with oil level with outer tube. pump dampener rod 10+ times to remove air and to fill it. refill to oil level with outer tube. pump fork several times using only ~6" of travel. let sit for several minutes. repeat oil fill process. then bleed oil down to proper level. i used a syringe and capillary pipette marked at 115mm from top of outer tube. then reassemble.

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JTI, I used a childs ear suction bulb stuck into a BIC pen housing, on mine I measure 95mm on the housing of the pen and mark it, then I just stick it in the top of the fork and suck it out to that level(with the forks compressed and the springs out). I have 4 kids and every time you leave the hospital with a new baby they give you a rubber suction bulb thing. Mike

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