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Thread: CC Fork Project - Lengthening them 10mm and installing small lugs

  1. #1
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    Lightbulb CC Fork Project - Lengthening them 10mm and installing small lugs

    Hi!

    So, Iíve found that I like the AER forks on my 2019 bike on the 2nd groove for general XC use and the 1st groove for sand riding. I have a set of 2013 CC forks, (done by PG suspension back in the day, with JBI pro perches) that I like VERY much. They are 10mm shorter than the new air forks. In order to get the same set height, I have to run them WAY down in the clamps, and it occurred to me a while back that I should just lengthen them to the length of the AER. I have most of the parts lying around to do it and am planning to take them apart to fit small axle lugs anyway. I figured Iíd make a post to share my plans in case anyone here has done something similar, and/or might find it interesting.

    The long damping rods from an OC fork used the same piston holder, so I expect the machining on the piston side of the rod is the same as it is on the CC rod. Much like how folks are shortening AER cartridges, I should be able to cut the other side of the rod down so that it is 10mm longer than the CC rod and thread it with an M12x1 die. Obviously, Iíll need an adjusting rod that is also 10mm longer than the OEM CC rod.

    Iím not sure if the cartridge can deal with 10mm more stroke before things crash. I honestly think it can, but will have to measure it when I take the forks apart.

    Even if the extra 10mm of stroke doesnít actually crash anything, it may cause another problem as I suspect the internal pressure may rise too much and pop the pin valve late in the stroke. I know there were tuners using stiffer springs on the pin valves, maybe I should source some of those?

    Alternatively, if Iíd rather limit the stroke, it should be as simple as making an extended ďcounternutĒ that is something like 5-10mm longer than the OEM one.

    The trouble with that is that if I limit the stroke the full 10mm that I have extended it, I wonít get as far into the bottoming cones. I happen to have an old set of 2009 CC tubes that I can rob the earlier, longer bottoming cones from, and then turn them down until theyíre 10mm taller than the later cones, if thatís the best idea.

    Obviously, Iíll need 10mm of preload spacers as well to get this done. I have an acetal copolymer rod that I have cut those out of in the past, so that shouldnít be an issue.

    Am I missing anything? How would the other suspension fabricator types go about this? Assuming we have room for the whole extra 10mm of stroke, do you think the pin valve opening early will be an issue, causing my cartridges to always be "under-filled?" I'm trying to figure out what negative affect the pop off valve would have if any. Assuming I limit the stroke so that itís the same as stock, does my idea to modify the earlier, taller bottoming cones make sense?

    Thanks for any input! Iíll post pictures as we go if thereís interestÖ
    -Walt #728
    2019 KTM 300 XC
    2018 KTM 300 XC Hybrid ATV GNCC # 728
    '2015' KTM 525 XC ATV
    2009 KTM 525 XC ATV
    2009 KTM 450 XC ATV
    2013 KTM 250 XC
    2002 Cannondale C440

  2. #2
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    Default Re: CC Fork Project - Lengthening them 10mm and installing small lugs

    You could install 10mm shorter top out springs. Its the easy way. Cam.

  3. #3
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    Default Re: CC Fork Project - Lengthening them 10mm and installing small lugs

    Interesting thought! I'll have to look for some of those. The parts fiche shows them as "SPRING REB. L=32 C=37 DI=13,9" So I'm guessing 37N/mm rate. I'll see if I can find anything at or a tiny bit stiffer than that rate in a 22 mm size. Maybe I can find one that's 5 mm shorter and still mod those OC rods to be 5mm longer... We'll see!
    -Walt #728
    2019 KTM 300 XC
    2018 KTM 300 XC Hybrid ATV GNCC # 728
    '2015' KTM 525 XC ATV
    2009 KTM 525 XC ATV
    2009 KTM 450 XC ATV
    2013 KTM 250 XC
    2002 Cannondale C440

  4. #4
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    Default Re: CC Fork Project - Lengthening them 10mm and installing small lugs

    To shorten forks I have used 454 chev valve springs. Exactly 2" shorter. You may be able to find a similar sized shorter spring online. Heck who knows, briggs and straton valve springs. I went to a engine rebuild shop and dug through their bucket of old springs. Can always cut the stock one shorter too. Cut the spring and then heat the end to make a flat. If the contact surface at the modded end is steel then should be no issues. Cam.

  5. #5
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    Default Re: CC Fork Project - Lengthening them 10mm and installing small lugs

    hmm... These may be close, and would get me to 949mm which is plenty close enough. https://www.centuryspring.com/catalo...lar&id=12577CS but I would probably need to make a new spring guide bushing since the ID is 14.35mm instead of 13.9mm... I'll have to get the cartridges apart and take some measurements. Thanks for the idea!
    -Walt #728
    2019 KTM 300 XC
    2018 KTM 300 XC Hybrid ATV GNCC # 728
    '2015' KTM 525 XC ATV
    2009 KTM 525 XC ATV
    2009 KTM 450 XC ATV
    2013 KTM 250 XC
    2002 Cannondale C440

  6. #6
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    Default Re: CC Fork Project - Lengthening them 10mm and installing small lugs

    I personally would just run them flush with the clamps. Can also run a longer linkage to balance chassis.

  7. #7
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    Default Re: CC Fork Project - Lengthening them 10mm and installing small lugs

    Wouldn't it be easier to shorten the shock with a small spacer or so or a longer link like AC said.

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