Tuning tech forks with oil level

Discussion in 'Trials' started by Beavis353, May 6, 2020.

  1. Beavis353

    Beavis353 Been here awhile

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    I'd like to better understand the effects of oil volume/air gap for tech forks. Anyone care to share their experiences with tuning forks by adding or subtracting oil to the left or right side to tune for their particular needs?

    Thanks
    :beer
    #1
  2. Cascao

    Cascao Been here awhile

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    If you look at tech forks manual, you will see that montesa has a higher oil level than others. Probably due heavyer weight.
    It is a starting point for you
    #2
  3. lineaway

    lineaway Long timer

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    More oil would firm up the left side and you could lose travel. LIghter on either side would speed it up
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  4. Beatprojim

    Beatprojim Beatprojim Supporter

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    Oil does not compress, while air does. The fork has a finite volume so increasing the oil to air ratio (less air gap) means there is less air to compress and the fork will feel firmer as it closes on bottoming. (extra oil only firms up the last part of the stroke) As Cascoa said, the specs on the Tesa have extra oil to hold the extra weight up. So the same would hold true for a heavier rider or someone taking bigger hits. As Lineaway said, too much oil and you loose usable stroke. Best to get a band on the fork and measure what kind of hit takes it too fully stoke. If you think it bottoms too easy add 10 - 15 ccs and try it again.
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  5. slicktop

    slicktop Long timer

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    Nice.
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  6. mung

    mung Long timer

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    When I bought my 12 Raga there were no stiffer fork springs available. To match the one step stiffer shock spring I raised the oil 25 mm and used 10 wt. oil. Opened the compression and rebound clickers a few turns and they worked very well. Raised oil level only stiffens the fork near the end of the travel and the rest of the time it works like normal. Springs would have been better but has worked well for nine years now.
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  7. Cascao

    Cascao Been here awhile

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    Tech forks has a end stroke valve acting on last 50mm of travel. Check if yours is closed. It can help with bottoming.
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  8. Gordy

    Gordy SUPPORTER

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    Raising the oil level is just a bottoming stop adjustment. If you add too much, it will become harsh due to hydro-locking but you have to add quite a bit to get there. lf your fork feels like it is bottoming harsh at the end of travel (like on a hard zap or drop off) adding oil may help. If the problem that you ‘think’ you have is something else, then adding oil might make your problem worse.
    #8
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  9. motobene

    motobene Motoing for 49 years Supporter

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    Some refer to the closed volume of air as the secondary spring, and that's right. There's oil level and also where in the travel you screw the cap on. If not fully extended you'll start out at full spring extension at a negative pressure. Because the spring displaces air volume, it's not easy to figure out where the practical limit of the air bubble is. Back when forks were less good I'd mess more with oil levels. With the moderns I just stick with what I find in there from the factory at the first oil change. If not obviously wrong I write that down and stick with it if I like the action.

    Cascao is right to point out Tech's end-of-travel blow-off adjuster.
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  10. Huzband

    Huzband Team Dirt

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    Does the spring not also displace oil volume?

    This can certainly be over-thought, yes?
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  11. Cascao

    Cascao Been here awhile

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    The coil spring is almost linear.
    Air trapped inside both sides of forks are spring too. But an progressive spring. Less air is more progressive.

    Please keep in mind that tech forks are good forks and doesn't need modification to work well. Proper technique help wonders with end course events during big hits. At speed, trials bike will always call attention.

    Sometimes is important to archieve end stroke to be able to lift bike. A too progressive fork can be worse in this kind of obstacle since energy will be wasted (absorved) on hidraulic circuit.... and a higly tuned front fork will not work propely if rear shock is standard.

    #11
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  12. PMK

    PMK Been here awhile

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    Yes and no. In simple terms, if the spring is not changed, the oil level tuning in small increments typically alters from midstroke to bottoming.

    If the spring is replaced with anything except the same part number, then the springs volume (plus rate change) does make it possible oil height may need to be readjusted.

    Getting really technical, some tuners will measure the springs volume, and know exactly how much change it makes, and use that known difference in spring volumes to alter oil height when the spring is installed.

    Before altering oil levels, the bike should be ridden / tested after fully releasing any air build up inside the fork tubes. Some dirt bikes have vent screws, other may not and require loosening the upper fork cap.

    Releasing air build up often is a good thing.

    On a side note, vintage bike forks, such as Betors and Ceriani had check ball vents. The check ball setups, released air pressure during compression of the fork. With this setup, oil level is only important regarding covering the damper rods. Pretty much close enough is good enough. On my MAR, I did away with the check ball setup and converted to Shrader valves. This allows easy releasing of air build up, and adds progression as the fork compresses.
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  13. DyrWolf

    DyrWolf Long timer Supporter

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    Zap vs splatter suspension balancing?
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  14. PMK

    PMK Been here awhile

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    If needed I guess. Seems everything in this sport is about balance.
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  15. Norman Foley

    Norman Foley Devotee of the Husqvarna Supporter

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    You might look at it like this..... Ryan Young in his schools emphasizes that the zap will limit the height you can jump up, as you progress. You need to learn to splatter, if you are going to be riding higher obstacles in the more advanced classes. So lower level riders want a bike that zaps well, and higher level riders want a bike that will do the splatters.
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  16. DyrWolf

    DyrWolf Long timer Supporter

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    I was just stirring the pot
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  17. lineaway

    lineaway Long timer

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    Lower level riders just need to learn when to gas it.
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  18. 2whlrcr

    2whlrcr gooligan

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    When in doubt, twist n shout!
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  19. Norman Foley

    Norman Foley Devotee of the Husqvarna Supporter

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    I’ve watched lots of lower level riders do just that.... twist and shout when they center punch an obstacle instead of lifting!
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  20. Huzband

    Huzband Team Dirt

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    @playinatwork will argue with you about this. :lol3
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