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Thread: Fork Oil - changing

  1. #1
    Senior Member TW_in_BC's Avatar
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    Apparently, I should have changed my fork oil a while back............a LONG while back. I'm too embarrassed to say how long it has been, but I've got the parts on order now.

    I am a huge fan of synthetic oils and I've heard about using Automatic Transmission Fluid in the front forks. What I need to know is, can I use synthetic ATF (which I have on the shelf) instead of the usual Fork oil (which is one the Dealer's shelf)?
    Bob Suggs and WyoCoyote58 like this.
    2008 TW200
    Southwest corner of BC Canada

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  2. #2
    Senior Member lizrdbrth's Avatar
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    It depends. Dinosaur Dexron is about 9wt. stock spec is 10wt. Works fine.



    Dino Dexron/Mercon on the other hand is too thin. Only 4-5wt.



    You'll need to get the actual viscosity of the brand and type you have at hand before trying it.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  3. #3
    Senior Member JarrodWeaver's Avatar
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    When I rebuilt my forks I added PJ1 15W and dont like the stiffer action of the forks. Need to swap back to something lighter.

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  5. #4
    Senior Member twjay's Avatar
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    I just changed the fluid in my forks and used Mobile 1 synthetic ATF. It works fine. I added 3/4" spacers to the fork springs, so the ride is firmer on short street bumps at speed, but off-road, the inital

    feel of the fork is stiffer, then there is no difference through the rest of the fork travel that I can tell.

  6. #5
    Member BuddyMc's Avatar
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    Thinking that my 09 TW with just 108 miles (purchased in Dec 11) had sucked up moisture during its storage, I changed the fluid. Discovered one folk had only 6 oz and the other 6 1/2 oz of perfectly appearing cranberry colored Yamaha oil. Took the opportunity to insert 3/4" poly spacers for more preload plus precisely 8 oz of Honda's 5wt fork oil in each leg. The added preload keeps the bike riding higher in the forks, while the lighter fluid really softens the forks action when in the rocks. When combined with 8 - 10 psi in the tires the suspension works 3x better for me (225 lbs) than stock. No more bottoming or jarring even when ridden aggressively. Diving under front braking is predictable and much improved as well. In addition, with the correct air pressures the bike is very civilized on the road riding single or doubled up. The combination of BS 302 3/4" preload and a lighter fork oil works well for me as so far the bike is much more sure-footed in all conditions.
    owtcast likes this.
    Huntsville, Alabama - Have TW, Will Ride! All White 09 TW, D2Moto Pegs, Bridgestone 302 front tire, 2" higher bars, 3/4" fork preload spacer, 5wt Honda fork oil, 135mm fork oil level, exhaust tip mod, 2.5 turns out fuel mixture, 0.060 in needle shims, 130 main jet, 14/47 sprockets, 20w-50 Valvoline MC full synthetic oil, ImmixRacing rear rack, Bilt Bag on Rack, 1" front fender spacers, Battery Tender connections on new battery (installed 12/11), Coleman ATV seat cushion, 2 Agri Supply tool tubes, 30oz MSR Fuel Bottle, auxiliary 6 LED tail light, Sylvania Silverstar Ultra H4 headlight bulb, 2357 turn signals, and Superbright's 1157 LED Motorcycle Tail Light Bulb with 19 red & 6 white LEDs. Shortened rear turn signals. Bypassed kickstand switch.



    Plus a "new to me" 1995 Yamaha Virago XV 750G for Pavement Purposes!!

  7. #6
    Senior Member PalmStateCrawler's Avatar
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    What are you guys using for spacers?
    '13 690 Enduro R too many frickin farkles...
    '07 KLX250 farkled (wife's bike)
    '86 BW80 farkled to size
    '10 TW200 you will be missed

  8. #7
    Banned qwerty's Avatar
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    What do you have sitting around? Plastic, steel, or aluminum pipe or rod will work, as long as the outside diameter will fit in the fork tube. Even a couple stacks of flat washers will get the job down.




  9. #8
    Senior Member lizrdbrth's Avatar
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    I hesitate to say this due to the potential for fork seal failure and ickygooey death among the uninitiated. Fork setup is a process. But here goes:



    A).If you're using the 8 oz. measurement in the manual you're getting NO fork action and ZERO rebound damping, regardless of oil viscosity. The springs are doing all the work and you're getting just enough compression damping to keep them from flailing the breeze. Cutting spacers to give more preload will only give you a warm feeling and stiffen up the spring, period. There isn't enough fluid left for the rebound orifices to do anything. Placebo effect.



    . If you're using the 135mm oil height measurement listed in the manual, see above.



    C). If you don't understand why this is so, use the 135mm measurement. The factory numbers are wrong, but the 135mm measurement is the least wrong and by far the safer of the two.



    D). If after educating yourself on the process you are willing to increase the height incrementally by a few mm's at a time you probably won't even need a viscosity increase. Use too long a spacer and no amount of viscosity increase will fix it.



    A few factoids about your TW's forks:



    You have EXACTLY 6 inches of available travel. Not 6.3", 6.5", 7.0" or any of the more optimistic numbers you may read on the web. 6.00000000000000" TOTAL travel before metal hits metal.. Of this you have to "give up" a quarter of your travel for proper setup (You're not really "giving up" anything, but some folks seem to think they are).



    Correct sag if kept to the bare minimum should be 20-25% of total travel. Cut spacers ONLY until you get 1 1/4"-1 1/2" laden sag under your own weight in full riding gear, no less. There is no "one size fits all" spacer length, there is only the one (or none) which applies to YOU, at YOUR weight on YOUR bike, carrying YOUR stuff.



    Do the rest with oil after reading up on the concept of how air-over-oil non-cartridge forks work. No, you won't get this right in first attempt and it's entirely possible that you may not even get it right by the fifth attempt, but the results will be worth it.



    Gsmith2030 and WyoCoyote58 like this.
    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  10. #9
    Senior Member PalmStateCrawler's Avatar
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    So, adding a little more oil will "stiffen" the forks by decreasing the amount of air in the tubes? The reason I ask is, when riding offroad with the front rack on, it tends to hit my front fender and I don't want it to crack!
    '13 690 Enduro R too many frickin farkles...
    '07 KLX250 farkled (wife's bike)
    '86 BW80 farkled to size
    '10 TW200 you will be missed

  11. #10
    Senior Member lizrdbrth's Avatar
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    Few TW owners have any clue what a properly working fork feels like because they've never felt their rebound damping. These forks blow, but not to the extent they're often blamed.



    The other issue is that factory fork oil level recomendations are intended as a BASELINE. It is assumed the end user is aware of that, so let's not be too quick to jump all over Yamaha. The rec's are warranty-driven and aimed at saving themselves against dinks who do stoopit stuff like filling them with 90wt.



    We not only have compression damping, we also have rebound damping. But rebound damping requires that there be fluid above the orifices when the fork reaches the bottom of travel. So one reason to adjust the level is to get this feature to operate as intended. You can't get there with either of the manual's measurements as-is, but if you go too far you'll blow seals on compression. If you can't get both features to function simultaneously at your weight and with the correct laden sag, then (and only then) is it time for heavier oil.



    This is a process and if you're not willing to sneak up on it incrementally you should just use the factory rec's and let it be.



    IMO going lower than 10wt. completely negates any chance of seeing rebound damping at all, even without spacers.



    I run longer tubes with TW internals, so my settings won't apply to anyone else's situation, and Purple weighs 110 lbs. soaking wet and needs SHORTER spacers to get enough sag. As you might imagine I've been through the process a number of times and had to do it all over again with the longer front tubes.



    Here's a pic of what you're dealing with. This is your damper rod, or tube. The allen head bolt on the bottom of your forks bolts into this and keeps it centered in the lower legs. It then slides up and down inside the fork tubes, effectively dividing them into two chambers. One above the white ring, one below:







    The two tiny holes in line with one another at the top are the rebound orifices. They're smaller to slow the return of fluid because the spring forces are greater in rebound.





    The staggered, much larger holes at the bottom are the compression orifices. There are 2 more on the other side, total of 4.



    Thicker oil slows down BOTH compression and rebound in a more or less linear fashion. Sometimes this is a good thing, but only up to a point. Thicker oil has a downside in that after a given viscosity it won't flow through the smaller orifices in time to replenish the compression side and it will reach a point where it just sits in hydraulic limbo unable to make a decision, indefinitely.



    In general the best approach is to use the thinnest oil possible to get the job done. Yamaha's fork supplier sized the orifices around 10wt. oil flow characteristics so your first and best course of action is to try to get the thing to work with 10wt. oil. Learn the ziptie drill and see it through.



    (Note the corrosion on this tube. This came from a bike that had been sitting for a couple of years. The tubes were rusted and the compression holes were completely clogged with sediment. This is why it's never a bad idea to completely dissassemble the forks on an old bike. At minimum a thourough flush is in order unless you knowfor a fact that the bike was maintained meticulously. This bike had plenty of fork oil, but it was contaminated by moisture. That's why fork oil needs to be changed regularly, even though in theory it never breaks down from heat like the oil in a crankcase. In essence it is always raining inside your fork tubes.)



    Anyway, under compression the fluid gets forced from the lower legs, through the lower holes into the upper fork tube. In rebound it gets sucked back through the two tiny rebound holes and returns to the lower legs. If there's nothing above it but air you get no rebound action.



    The fork will also bottom easily because the air gap is too great.



    You need to get these two items balanced. So you see the solution has more to do with oil volume than viscosity.



    While our forks are incredibly simple devices the concept of their operation can be difficult to grasp until the light comes on in your head, so don't feel dopey if that applies to you. I recomend you cruise the 'net and read as many explanations as you can until you grasp the concept. They really are inanely simple, but we all learn differently so read all you can til someone's explanation sticks. Some people may need to take one apart before the light goes on. Don't matter how you get there as long as you do.



    Somewhat of an oversimplification, but essentially all that cartridge-type forks and emulators do is allow you to vary the size of the orifices at will. Our forks have fixed orifices, but MOST of the same changes can be made through a combination of air gaps, spring preload and viscosity.



    If all of this seems like a PITA, it is. This should also help to explain why some of us dislike the later models, or more to the point, what Yamaha did to cut corners on the later models. The absence of fork drains is no longer a minor inconvenience, is it? Their absence discourages both routine maintenence and proper setup in one swell foop.



    Gsmith2030 and WyoCoyote58 like this.
    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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