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Thread: CT70 Fork Seal

  1. #1
    Burke299 is offline 50cc
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    CT70 Fork Seal

    Im rebuilding my 1979 CT70, I purchased the front fork re-built kit and I want to make sure I install the fork seals properly.
    Does anyone have a diagram or know the best way to get that done?
    Ive read that the take 3.2oz per fork, is that also the case?
    Thanks in advance!

  2. #2
    scooter is offline 120cc
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    How far are you in the process? Are you looking for disassembly steps. The rebuild is just the opposite of the disassembly

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    Soundwav's Avatar
    Soundwav is offline 90cc
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    Quote Originally Posted by Burke299 View Post
    Im rebuilding my 1979 CT70, I purchased the front fork re-built kit and I want to make sure I install the fork seals properly.
    Does anyone have a diagram or know the best way to get that done?
    Ive read that the take 3.2oz per fork, is that also the case?
    Thanks in advance!
    3.20z per fork is right..
    i just did mine last night.... 1 tip i can give you is the 3.2 is a base line. put in as much or little as you need its all about how the shock feels to you.
    3.2 is a nice setting but may be hard for some people or too soft for others.
    i think i put in to much on mine as the shocks are hard.. but that can all change when you get out on the road.
    ALSO depends on the weight of the oil you are using. i used bel-ray fork oil 20 weight..
    ive seen most people use 15-20w but once again its all about how the shocks feel to you.

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    racerx's Avatar
    racerx is offline Super Moderator
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    I'll second Burke299's comments.

    The quantity & viscosity of oil used can make a big difference, as does speed. 15w fork oil is a good baseline. If you're a lightweight rider, then 10w might be a better choice. If you're a large-mass individual, then 20w might give you a better result. Chinese knockoffs, lacking internal valving, can benefit from the use of 80w or 90w gear oil. A heavily worn OEM fork leg might need 20w to give the same result as a tigher example with 10w or 15w. There's some trial & error testing in your future if you want to realize what you consider the best results.

    In terms of oil quantity, that's where the largest effects are to be found. The process is a little tricky for the first-timer. It is, in effect, somewhat akin to finding a midpoint compromise between "on" & "off". 10cc of oil can take a fork leg from as stiff as is practical to hydrolocked at partial compression. Armed with that knowledge, all you need is a measuring device and some common sense. Once the fork legs have been filled with the specified oil quantity, add 5cc to one, replace the upper plug & test the action. Then add another 5cc and restest...repeating the process until you just notice the action stiffening near the point of bottoming-out. That's the point where you can go over the proverbial cliff. You could try another 5cc, at this point, to see what happens. If you lose fork travel, then you'll have to drain those 5cc to get it back. Since you've noted the total amount of oil added to the one fork leg, you can simply add the same amount to the other side and you're done. If the fork action is still too soft, then it's a question of stiffer springs or heavier oil.

    This kind of fork "tuning" is unlikely to replace real tuning, done by a suspension pro. However, it can produce surprisingly good results. IMO, it's possible to get 20-30% improvement over OEM stock. If your fork was really whipped as you received it, then this (along with a rebuild) might give you better than a 100% improvement.

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    kziolk's Avatar
    kziolk is offline 90cc
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    The trapped air acts as an additional spring. The problem is the "air spring" is very progressive and gets too stiff too fast when there's too much oil. In the old days we used to drill and tap the fork cap and screw in an air valve similar to a valve stem. This way we could add small amounts of air to pressurize the fork to increase the spring pressure. This had an added benifit of sealing leaky fork seal also. Kevin

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    Burke299 is offline 50cc
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    ct70 fork seal follow up..

    Thanks for the feedbacks.
    Does anyone have or know where I can get a diagram of how to properly re-fill them?
    Its been a while.

  7. #7
    racerx's Avatar
    racerx is offline Super Moderator
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    Quote Originally Posted by kziolk View Post
    The trapped air acts as an additional spring. The problem is the "air spring" is very progressive and gets too stiff too fast when there's too much oil. In the old days we used to drill and tap the fork cap and screw in an air valve similar to a valve stem. This way we could add small amounts of air to pressurize the fork to increase the spring pressure. This had an added benifit of sealing leaky fork seal also. Kevin
    I suspect that pressurized air would cause a lot of oil leaks in CT fork legs. Probably wouldn't hold long anyway, especially with wear/rust/pitting on the area swept by the fork seals. Might be worth trying, for someone who knows what he's doing. For most, better to keep things simple.


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