Regarding fork oil levels...
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Thread: Regarding fork oil levels...

  1. #1
    Senior Member TW_in_BC's Avatar
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    Regarding fork oil levels...

    As referred to in this thread:
    https://tw200forum.com/forum/technical-write-ups/2786-fork-oil-changing-2.html


    Now, correct me if I'm wrong...but shouldn't oil level be checked with the forks in a VERTICAL position, with springs removed and the fork fully compressed?
    How does one adjust the oil level in the forks, while they are still on the bike...how do you get the forks to stand vertically AND fully compressed to add/subtract oil?

    Or am I over-thinking this?

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    Senior Member scotti158's Avatar
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    I had to remove my forks to drain them, no drain screw on mine. I did have them vertical when I added and measured the oil level. I understand what you're saying, if the forks are on the bike, the are angled, therefore the oil level will be angled and read differently if you measure from the forward rim or the rearward rim of the fork. If your forks are already on the bike, I would measure each fork from the same side, front or back, just do them both the same. I think it's more important to get them as close to the same height than getting an exact mm distance from the top of the fork.
    2013 Yamaha TW200

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    rbm
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    Quote Originally Posted by TW_in_BC View Post

    Now, correct me if I'm wrong...but shouldn't oil level be checked with the forks in a VERTICAL position, with springs removed and the fork fully compressed?
    Yes...

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    Senior Member TW_in_BC's Avatar
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    So I'm wondering then...once I get the laden-sag part done, why couldn't I just adjust the level and "work" the fork off the bike until I got the best action from it. Then I could measure the level and duplicate it on the other fork and then install them...
    As long as I don't go over the 100mm level...right?

  6. #5
    Senior Member scotti158's Avatar
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    I think to get the proper ride action, you need to test ride it. Just pumping them up and down off the bike wouldn't tell you anything about actual ride quality. Another thing I forgot to mention, when filling any empty fork, get your level where you want it, then pump the fork a few times to get the air out, then re-measure.
    2013 Yamaha TW200

    1996 Yamaha TW200

    1995 Kawasaki KLR650

    2002 Yamaha RoadStar 1600 with sidecar

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    Senior Member supachip1's Avatar
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    perfect timing for me as i am just doing my first fork oil change…so as i understand if i want it harder i increase the oil level slightly..say 10mm…or add a spacer of the same 10mm etc, but don't fill oil above 100mm?? my purpose would be for only road riding….we only have 1 road on the island where i live and its 5km long in total!!!

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    Senior Member elime's Avatar
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    Before I changed my fork oil they would bottom out over every little bump. I explained to Lizrdbrth that I thought his tutorial was very nice but way more work than I wanted to do, and that I was looking for improvement, not perfection, and he understood.

    Long story short, he said to set the oil level at 130 mm. I did and I haven't touched the forks since. I can still bottom out the forks if I hit something super hard but I don't ride that way -- and if I did I would need a beefier bike than the TW. Setting the oil to 130 mm made a big difference. I also recall him saying if I went less than 120 mm there was a real chance of blowing out the seals -- so be careful with the 100mm level I read some people suggesting.

    The other thing to do is measure the oil level before you pour it out. Let it drain off the springs so you get an accurate measurement. Mine was at 157 mm. According to Lizrdbrth < 135 mm it isn't doing any good. I believe him!

    My 2 cents worth: The air inside the shock acts like a spring. As you increase the oil volume you decrease the air volume and the "air spring" gets stiffer. Tony
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    Senior Member supachip1's Avatar
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    thanks Tony….that was my understanding too, i have done all the above and set the oil level at 127 for no reason other than that was what i had poured in and didn't think the extra 3mm was worth pouring out or would make any difference to how i use the bike…guess i will find out soon

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    Senior Member elime's Avatar
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    Quote Originally Posted by supachip1 View Post
    thanks Tony….that was my understanding too, i have done all the above and set the oil level at 127 for no reason other than that was what i had poured in and didn't think the extra 3mm was worth pouring out or would make any difference to how i use the bike…guess i will find out soon
    I doubt if 3 mm will make any noticeable difference and if you are going to make a mistake a little to much oil is better than not enough.

    Anyway, once you get it all back together and tried it out report back here your findings. Good, bad, or no difference report back so others will know what they can expect. Tony
    Long live the internal combustion engine!

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    Senior Member old white truck's Avatar
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    Quote Originally Posted by TW_in_BC View Post
    Now, correct me if I'm wrong...but shouldn't oil level be checked with the forks in a VERTICAL position,... how do you get the forks to stand vertically AND fully compressed to add/subtract oil?
    Or am I over-thinking this?
    I like this question because I am frequently guilty of ever-thinking.

    Check my reasoning and math but here are my quick guesses about the vertical/angled measurement issue.

    IF you measure to the exact center of the tube when you are measuring down from the top, it will not matter whether your fork tube is at its normal angle or perfectly vertical - you will end up with the same quantity of oil either way.

    But, it is difficult to measure to the exact center of the tube diameter.

    However, it does not make a big difference even if you measured down along one of the tube edges rather than the center - there would only be a small difference between a vertical measurement and a on-bike (angled) measurement. If I assume the fork angle is 28 degrees off vertical and the inside diameter of the tube is 1.2 inches then by my hazy late Saturday calculations the volume of oil difference would only be 0.20 ounces or 5.9 milliliters. (Someone should check me on this - I could be all forked up).

    All that being said, I always fill and measure mine vertically.

    I saw a neat and simple tool for setting the oil level - you first put in a bit too much oil and then you suck out the extra until you get to the right amount: Tusk Fork Oil Level Tool | Dirt Bike | Rocky Mountain ATV/MC

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