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Why change the fork oil?

Discussion in 'Bling and Appearance' at netrider.net.au started by Paulstar, Mar 27, 2009.

  1. Hy guys

    I have my bike up in the air at the moment with the front wheel off getting the bearing replaced and im wondering if anyone can tell me what noticeable difference i might get if i change the fork oil. There is no leakage or anything like that of my forks but its part of maintenance right?

    What will changing my fork oil do?


     
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  2. pm Loz as he is the fork oil guru around these parts...but fork oil degrades over time, just like coolant, brake fluid etc...I know you can change to heavier or lighter fork oil to change the handling of the bike...I'm pretty sure Loz has done this on his Minja

    :)
     
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  3. Thanks Bamm-Bamm i have PM'd Loz to please post here so standing by :)
     
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  4. PISS OFF.
     
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  5. Just kidding. :grin:
     
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  6. OK I'm no sort of guru but I can tell you this:

    Looking at the age of your bike, I'd guess the oil in your forks has probably not been replaced for a looong time (if ever) and it's probably well and truly rooted. You'll see that it's got a milky sort of texture when you pour it out. It's clear when it goes in.

    I'd change it for sure, it's a very quick job.

    The decision becomes whether you want to use standard weight oil (usually 5w or 10w) or go a bit heavier. Heavier oil increases the damping properties - if you go for a 15w or 20w oil you'll notice the forks feel firmer and don't tend to divs as much under brakes. On the other hand, being firmer, they may cause bumpy roads to be a bit less comfortable.

    But then, I almost always find the suspension on those old 250s to be really sloppy.

    I'd tend to recommend 15W oil to most people, and 20W to big fat buggers like myself. But at $15 a bottle, it costs bugger-all to try something and go back to 10W if you don't like it.
     
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  7. Or you could go all retro and brew your own from various blends of engine oil and ATF, like everyone used to before you could buy fork oil off the shelf everywhere :shock: . Everyone who bothered to change their fork oil.

    Hmm. Maybe the fact that all 70s and 80s Jap bikes had crap handling wasn't all down to the manufacturers :LOL: .
     
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  8. Would firmer forks equal less braking because there is less weight transfer?

    I'd be happy if it dived less when on brakes and i imagine that i can manage on bumpy roads with a bit more bumps.

    Sounds like a worthwhile exercise!
     
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  9. I think that less fork dive means that there is more fork travel available during braking, so the suspension can still act on bumps in the road rather than bottoming out.

    I'm not an expect at physics, however if you have well setup forks that don't dive so much you should have better braking than if you have poorly setup forks that do dive - for the above reason. Above that I think braking technique and tyre condition are going to play a major role in how fast you can stop too.
     
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  10. There'll be plenty of weight transfer going on. I can stoppie (endo, in MTB speak) my old rigid-forked mountainbike. :) In fact it's even easier to brake hard on that bike than it is to brake hard on my hard-tail mountainbike.


    There are two things acting here:
    * The springs, which determine the 'steady state' condition of the bike. When the forks are not actually moving up and down, only the springs determine how much "dive" occurs.

    * The dampers, which control how fast the forks compress/rebound. Without dampers, the forks will act like pogo sticks, oscillating up and down uncontrollably. Extremely stiff dampers won't allow the forks to compress/rebound quickly at all.


    If you brake for long enough, a bike with thick oil and a bike with thin oil will actually have the same amount of "dive" during braking. The thin-oiled bike only seems like it dives more because the forks compress much much faster when you first apply the brakes.

    This is because the thin-oiled dampers don't offer much resistance to the diving motion - instead the spring must compress until it can slow down and stop the diving action on its own.

    Weight transfer to the front will actually be faster with heavier weight oil because the forks resist the diving action more quickly than a bike with thin damper oil. A bike with totally rigid forks would have the fastest weight transfer of all.
     
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  11. have drained the oil from the LHS and now stuck on getting the top half of the fork off to add more oil :oops:
     
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  12. Nothing ever goes wrong at the 1st step eh. Allllwwwways has to wait till you royally bunged doesn't it. Oh the joys.

    Lateral thinking. Flip the tube upside down if its not too hard to get off the bike. Or flip the whole bike upside down? Lol not sure if that will make other fluids leak (although DEFINENTLY Petrol)
     
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  13. i thought i had problems before...with a knife and a flat head i got the retaining clip of. Clip off, clamp loosned (used a G clamp to push the assembly down far enough to gt the clip off) and BANG we have lift off and parts are flying everywhere as i thought it would. Great! fill it with fluid, only minor things went wrong on that step :LOL: yay now the fun part. All along i;d been thinking wow so much pressure it was hard enough to get it out im going to have FUN putting it in.

    And i am...ZOMG :twisted: :LOL: :shock: so many emotions lol...

    i cant properly compress everything to fit back into the fork... :roll:
     
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  14. So i was able to assemble that side...without the spacer in the tube...it was impossible i tell you to re-assemble with that spacer :shock: ive drained the other side and am experiencing difficulty removing the retaining C clip...this is homo! i cant beleive they would use such an idiotic design, what crap?

    Does anyone foresee any problems with my not using the spacer? i cant even test ride the bike tis way because the driveway is blocked!
     
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  15. Ummm

    I hope you've measured the right amount of oil into each fork... Yes?

    Are you trying to get the fork caps back on with the forks still on the bike?

    That ain't gonna happen. Take them off, then hold the fork tube up with your left hand while you force the cap down with your right. Use all your bodyweight, you'll get it without too much problem.

    You need those spacers, yes. That's how the fork preload is set.
     
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  16. but but but the guys on fzr250 did it with the forks on the bike! No idea how! but they did? But since i cant see anyway to do it...the forks must come off :shock: so they shall..stand by for updates :p Thanks Loz! it seems i underestimated the size f the job!
     
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  17. Well i took the forks out which was very easy. The carefully wiped them off and put them in a big plastic bag and took them to the local motorbike mech :cool: i had already bought the fork oil $20 and they charged me $30 to change the fluid etc and have it all back together. They took under one hour which was good i had lunch and came back, it took less than thirty minutes to fit everything back to the bike and take it for a test ride :cool:

    Its a definite improvement with the new heavier fluid. The front end feels a lot more solid i can really jump on the brakes now without the bike feeling loose or unstable. I feel like the front brake isnt working as well as before but i think thats just mind tricks because the bike isnt movingup and down as much it feels like its brakng slower :grin: all in all im very happy with the improvement :!:

    Thanks for all the help :cool:
     
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  18. Dear me, you did all the hard bits and paid somebody to do the easy bit! Did you try forcing the caps on with your bodyweight? Works easy for me, but then again, I've got some kilos behind me.
     
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  19. :LOL: to me pulling the forks out was simple, undo all the bolts and slide them out.

    The caps just had an insane amount of pressure behind them even when the forks were drained. Im pushing with about 56kilos here :oops: i used a g-clamp on the handle bars to compress the right hand side one but there was no way of using that method on the left hand side. So i didn't have many options. Plus each time the clamp slipped parts went flying everywhere! so i cut my losses before i lost an eye :LOL:

    Its easily the dumbest thing i've ever seen with these C-Clips..they are not even circlips! :roll:

    :LOL:
     
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