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  1. #1
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    26" to 20" fork conversion... Off to a rough start

    I won this fork on Ebay
    ProFlex Mountain Bike Fork Shock | eBay
    It appears to be built like the Manitou that has been popular to modify here.
    I've been Googling for an hour trying to find an exploded view of the insides or rebuild instructions.
    Ulitimately, I'm going to dissassemble it and cut it down to a 20" fork.
    Does anyone know where to find an exploded view, or has anyone had one apart? There are allen screws at the bottom of each fork tube, and two more at the top of the fork tube. I turn them, and nothing happens. I don't know if they are for preload and rebound damping, or what. They don't appear to be holding the thing together. I need to get the cast lowers off the tube, and there appears to be rivits holding them on, so may begin by drilling them out. I'd really like to see the insides before just tearing into it though.
    Last edited by indianadave; 06-10-2013 at 04:43 AM.

  2. #2
    GMF
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    not many people will have experience with those forks as they are very old, i believe - early 90s IIRC. Should be just a very simple elastomer stack - no sophistacted damping or anything like that. Can't help with how it is put together, but it should be dead simple, and are are dealing with an internal shaft that is just spinning (or something like that).

    -Damon

  3. #3
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    Looks like a decent candidate for a 20" fork. Try using just one stack of elastomers in one side or convert it to a coil spring. Dual elastomer stacks are probably much to stiff for a kiddo. One difficulty I saw when I converted a manitou is that it takes a fairly long stack of elastomers to achieve much travel, by the time you have chopped the fork down, the resulting height available for the elastomers may not be long enough for much travel. A light coil spring will yield more travel relative to the free length before it bottoms out.
    I have never worked on this exact fork, but if it is anything like other elastomer forks there are long bolts going through the center of the elastomers, hopefully turning them CCW will unscrew and then should allow you to pull the lowers off the stanchion tubes. The retaining bolt heads can be either inside the stanchion tubes, accessible from top or else the bolt heads might be accessible from bottom of the lower (and threaded into the stanchion). Also look for snap rings at top of the stanchion that might be holding things together?? The retaining bolts are probably not also used for pre-load adjustment, the need to be tight so they dont loosen and let the fork fall apart mid-wheelie. Probably a second adjusment mechanism is it has external pre-load adjustment.

    Post more pictures of the configuration and dissassembly.....

  4. #4
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    Quote Originally Posted by GrayJay View Post
    Looks like a decent candidate for a 20" fork...
    +1.

    Can you remove the top caps? You may need to hold a nut or something similar in from the top.

  5. #5
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    Got it apart... Then failed miserably.

    [/ATTACH]Just got what I think may be a good 26" to 20" fork candidate.-6-9-13-001.jpgJust got what I think may be a good 26" to 20" fork candidate.-6-9-13-002.jpgJust got what I think may be a good 26" to 20" fork candidate.-6-9-13-003.jpgJust got what I think may be a good 26" to 20" fork candidate.-6-9-13-004.jpg [ATTACH=CONFIG]806811

    All I had to do was scre the preload screw in, and expose the allen heads so the top caps could be removed. Then I removed the springs, elastomers, and appled pressure to the inside bottom. There are knurls that keep the shaft from spinning when you turn the allen screw at the bottom of the fork tubes.

    Once apart, I cut the bottom of the tubes off, and took my dremel and started hogging out the tube from the casting. There's a protrusion from the bottom where the screw goes in. Hard to work around that.
    Got a lot removed and tried prying some of it out, and broke the casting. Bummed.
    At least I got it pretty cheap. Not much money lost.
    Might step back and figure out a way to salvage it.
    Or would someone here who's done one be willing to convert this one if I ship it to you? I have a new baby and barely have free time to ride, let alone mess with this deep of a project... Need to stick to bolt-on stuff, I think.
    Attached Thumbnails Attached Thumbnails Just got what I think may be a good 26" to 20" fork candidate.-6-9-13-005.jpg  


  6. #6
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    That's a bummer. It looks like the outer tubes are steel (crmo?) instead of aluminium. The small piece broken off probably won't affect the strength too much provided it doesn't cause a crack to propagate.

    Can you see any evidence of assembly compound (probably green loctite) between the components? You can try heating the dropouts with a heat gun and getting it appart that way. You will also need to make sure you can shorten the stanchion tubes otherwise the A-C will remain unchanged (although shortening the outers will drop the brake bosses to where you want them).

  7. #7
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    Yes. There is green loctite holding them together. I think the outer tube is aluminum.
    Haven't worked on the stanchion yet, but am afraid I'll rub into the same issue there.
    I'm going to re-read the couple other 26"-20" fork conversion threads, and do some Googling now that I have it apart and can relate to what they did.

    Leaving the stanchions alone would result in a cool downhill bike rake, though, huh?

  8. #8
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    Green loctite is a good sign. It means that the interference fit between tube and drop-out is not stupidly tight (otherwise the green loctite would not be required or the layer even if used would be too thin to see) and that the parts are not cryo-fit (where the dropout would be heated and the tube frozen for assembly). Heat is the only way to break the adhesive bond created by the green loctite. You will need to get the part to at least 325F to break the green loctite bond (500F if they used the high temp variant - unlikely). A heat gun should get you there, otherwise you need to use a propane torch. There may be an issue with annealing the aluminium through application of that amount of heat. I don't know the specifics off the top of my head, but some research via the internet should give you some info.

    Yes - leaving the stanchions their normal length would still result in the same A-C as a 26" fork - bringing the front end of the 20" bike up and slackening the head angle.

  9. #9
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    I think your broken fork-end casting probably is still useable if you can get the tube stub out. When I converted my manitou, key step was using a bare hacksaw blade to slowly cut a slot along length of the cut-off lower tube. Once there was a slot in the tubing, the press-fit tension is released and it is much easier to collapse the remains of the tube stub inward and then pull it out of the casting. Once you get it partially collaped inward, you can drill a hole in the tubing, put a screw through the hole so you have more solid connection to pull on.

  10. #10
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    Decided to keep going on this fork. At least I'll learn something.
    On the 2nd side, I cut the tube, drilled the rivit out (forgot to mention that previously) drilled a hole for a big screwdriver for leverage, and applied heat till I smelled the locktite. Then I gently tried turning the tube until it gave way. Then I slowly twisted it bak anf forth while pulling it out of the bottom casting. Came out much smooother, and the casting is intact.
    Just got what I think may be a good 26" to 20" fork candidate.-image06122013203203.jpg
    Just got what I think may be a good 26" to 20" fork candidate.-image06122013203543.jpg
    Also dissassembled the uppers, and they are threaded at both ends. Shortening these would result in having to re-thread whichever end you cut off.
    Just got what I think may be a good 26" to 20" fork candidate.-image06122013203531.jpg
    Just got what I think may be a good 26" to 20" fork candidate.-image06122013203225.jpg
    The other bottom casting is busted pretty badly. Maybe some of that Alumiloy I've seen informercials for may fix it?
    So anyway. If I come across another one of these cheap, I may pick it up. I have a machine shop at work, so adding threads back to the cut upper tube shouldn't be an issue. May ask the welders at work if they can weld up this piece.

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