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  1. #1
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    Default Sportster fork r bottom outs slowly under own weight?

    Hi, my buddy did a 6 over fork extension on his 14 irron. He put 12 ounces of 20wt oil that TC Bros sells in conjunction with their kit. Everything went together fine but his fork slowly bottoms out under the weight of the bike, when you lift the front it SLOWLY rebounds. I don't know much in the way of suspension, but I told him I'd post and see if anyone has any ideas.

    I know stock oil is Type E (which i believe is 10wt). Could the 20wt oil be causing this? He used the kit from TC bros and the supplied spaces. Nothing is leaking and everything went together fine, it seems.

    Thanks

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    did you, oh, 'your buddy', install the right length springs and spring spacers?

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    Hah, I'm not ashamed to admit when I fuck my shit up. I really am posting for him. I dont think he did springs. Just spacers that came with the kit.

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    did you help him with it? Hard to know what is wrong if it is not know what was done...perhaps just need to disassemble,check fork springs and spacers, call TCB.

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    I did help in the capacity that I was there and handed him stuff, but since I never had done anything like this I told him I wasnt calling shots on another persons bike with out having done the job before. We are gonna tear it down and start over, double check spacer measurements. But before we do that I suggested he call TC Bros monday and ask them.

  6. #6

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    If the fork won't support the bike, the fork obviously has too little spring. The spring holds the load up, the fork oil is just the damping medium.
    I believe most of those modern H-D forks require 1 - 2 inches of preload on the stock springs. Most aftermarket springs I am familiar with require some preload as well. What this means is that the spring and spacer stack will be above the threads in the top of the fork tube, with the fork fully extended, or even above the top of the fork tube itself. So, you have to force the top cap down against spring pressure to engage the threads.
    I've got the nifty little Trock clamp thing that makes this job easy. It also prevents launching the top plug across the shop upon disassembly. (I've done that before, too.)
    In any event, when you add length to the fork tube, you must add the same or nearly the same spacer length to the spring.
    Easy questions:
    Did you two add the same length spacer as you added length to the fork tube?
    Did you have to force the top plug down against spring pressure to engage the threads?
    Did you use the stock springs or were new springs provided in the kit?
    The answer to the problem lies within the answers to the above questions.

    Let me add that to tune these extended forks, sometimes a little shorter spacer can be used to reduce spring preload, to prevent extended forks from "topping out." But that is definitely not the problem here.

    Should be easy to sort this out.

    Jim

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    We used the Stock springs that came in the Iron, we used the 6.5 inch spacers that came in the kit. There was some pressure installing the caps but I am wondering if maybe the fork was not fully extended when they were installed. If the kit accounts only for Standard sportster forks maybe that is the issue as I believe Iron is under stock length?

    We will grab some PVC of the same diameter and thickness as the ones in the kit and remeasure.

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    Tell me more about your Trock clamp @Jim

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    Quote Originally Posted by brooklynbomber View Post
    Tell me more about your Trock clamp @Jim
    This is a little bar clamp like a woodworker 's clamp that Trock adapted to attach to the fork tube and put force on the top nut for assembly/ disassembly. I think Motion Pro and others offer something similar. It makes doing these forks with preload a one man job.

    Jim

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    Oh look, CC How To Tech thread from 2018:
    Thread: 6 over fork installation

    it includes a link to farmall's special tool to install stubborn fork tube cap nuts

    http://www.chopcult.com/forum/showthread.php?t=51109

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    Thanks everyone! We got it dialed. Turns out the fork was not "unloaded" when we did the spacers. So we got it on a stand, unloaded the fork and measured. turns out the 6.5 in spacers that came in the kit were 2 inches too short. Cut new spacers out of sturdy ass PVC we matched to the ones in the kit, and its good to go. Lesson learned, and now we know something new.

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    Does the bike have a stock rake????????

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    Glad it worked out!

    For those needing a spring compressor this works nicely:

    http://www.chopcult.com/forum/showth...160#post765160

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    Quote Originally Posted by Tattooo View Post
    Does the bike have a stock rake????????
    Yeah, I mentioned that. suggested at least new raked cup set. He doesn't seem worried about it and it isn't my bike so...

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