Misaligned Aluminum Horst Link Frame… how to fix?- Mtbr.com
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  1. #1
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    Misaligned Aluminum Horst Link Frame… how to fix?

    I recently began a project to restore my classic AMP Research B4 coil-sprung dual suspension frame (very progressive bike for its time and a weight weenie’s delight) into running condition. The frame material is T6061 alloy.

    Eleven years ago, my B4 and my wife’s nice GT RTS Team bike where securely locked and put on a rear-bike rack on my SUV. When left unattended for a period of time (irresponsible, yes, and lesson learned), the bikes were vandalized. Someone attempted to steal the bikes, probably with a crowbar, but could not get the bikes free from the rack. The GT was badly damaged and was ultimately scrapped. The B4, however looked unharmed. The thief, without success, then stripped as many bike component as they could without getting caught (wheels, bar, posts, stems, seat, etc. They even tried to take the cranks and fork!). Now, 11 years later, my worry is that my stripped down B4 didn’t escape damage; that the goons probably tweaked the seat-stay and/or the chain-stay - not enough to notice visually without wheels mounted- but enough for the bike to be inoperable.

    Once I put the wheels on, it was painfully obvious, because the wheel is off-center only on the chain-stay (i.e. the tire rubs severely the left inner chain-stay side – see photos) but is properly centered on the seat-stay. If both seat-stay and chain-stay position where off-center, then re-dishing the wheel might solve the problem, but this is not the case here.

    The question is what to do at this point? Can the seat-stay/chain-stay be re-aligned without damaging the frame, especially since the frame material is aluminum? There may be hope since the seat-stay and chain-stay are linkages and not welded to the frame. Maybe a custom frame builder could help with this?

    I have a call into AMP Research to determine if they still have the original jigs that were used to build/align the frames, and if they are willing to repair it, though I have my doubts as they are no longer in the business of making bikes (though I can still buy spare parts from them, but not whole stays). Is there anything that any of you can constructively recommend? I don’t want to give up on this splendid frame and piece of mountain bike history.

    Thanks in advance.
    Attached Thumbnails Attached Thumbnails -chainstay_length_view.jpg  

    -chainstay_length_view_closeup.jpg  

    -seatstay_top_view.jpg  

    -chainstay_under_view.jpg  


  2. #2
    Old school BMXer
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    In your photos, the wheel does not look centered between the seat stays or the chain stays.

    Have you flipped the wheel over to check the dish of the wheel?

    It probably doesn't help to say, but I started out riding suspension bikes on an RTS back in the early 90s. After newer designs came out in the mid 90s (LTS), I hated the way that RTS rode. At this point, I can't stand riding those RTS' any more. I was so glad when both of mine were gone.

    And while the AMP definately had a ground breaking suspension design, it had the rigidity of cooked pasta.
    May the air be filled with tires!

  3. #3
    RCP Fabrication
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    looks like wheel a wheel dishing issue to me. At least from the pictures, it seems to be closer on the non drive side, on both the seat and chain stays, but pictures are not as good as seeing it in person.

  4. #4
    nothing relevant to say
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    Take it to a local shop and find out if the frame is, in fact, out of alignment. Take your rear wheel too, and have them check the dish.
    To me, from the photos, it looks simply as the wheel is improperly dished. Alas, it could be the frame, somehow.
    Have it checked professionally.

  5. #5
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    Quote Originally Posted by Blaster1200 View Post
    In your photos, the wheel does not look centered between the seat stays or the chain stays.

    Have you flipped the wheel over to check the dish of the wheel?
    The wheel is actually centered on seat-stay, although the photo of the seat-stay doesn't do it justice. But not on the chain-stay where it is more obvious in the pictures. If it was dish, then you would see the same offset in both the seat and chain stays, correct?

    I will flip the wheel when I get back home, to check the dish out just the same.

    Quote Originally Posted by Blaster1200 View Post
    In your photos, the wheel does not It probably doesn't help to say, but I started out riding suspension bikes on an RTS back in the early 90s. After newer designs came out in the mid 90s (LTS), I hated the way that RTS rode. At this point, I can't stand riding those RTS' any more. I was so glad when both of mine were gone.

    And while the AMP definately had a ground breaking suspension design, it had the rigidity of cooked pasta.
    Yes, the RTS represents the now defunct non-active suspension technologies that were popular in the 90's, where the suspension was designed to operated without sag. It was also heavy and I didn't shed a tear when I collected insurance on it.

    the AMP, however was way better, active, and super light-weight and with Hoarst Link, it's one of the few active suspension designs to make out the 90's and into the present day. My AMP, by the way, was never noodlely. My old B2 rode solid also. Only the old B1's in circa 1991 were not that lateral stiff.

    But I digress...lets get back to the topic, please.

  6. #6
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    Quote Originally Posted by sealcove View Post
    If it was dish, then you would see the same offset in both the seat and chain stays, correct?
    No, not necessarily. Theres no real reason to assume that the spacing between the chain stays is the same as the spacing between the seat stays. So what is rubbing one chain stay, might clear the same sides seat. If you can take a clearer picture I can tell for sure, but thats what it looks like is going on. Its clearing the seat stays fine, but it is closer to the non drive side's seat stay.

  7. #7
    WIGGLER
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    An easy way to check it is with 2 bolts bolted into the dropouts where they almost touch
    This should show you if the alignment is off and by how much usually the cheaper bolts
    Are threaded all the way to the head or you could also use threaded rods

    I had a Mongoose licensed Amp B1 back in the '90s fun bike replaced the rear
    Shock with a Noleen.

  8. #8
    nothing relevant to say
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    Also, Maybe try another rear wheel, without a tire on it. I don't think you dumb, but make sure the axle is seated completely in the dropouts, too. (ya never know)

  9. #9
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    I don't know what's actually bent on this frame, and I don't know if they changed the chainstays between models, but I have a B2 rear end that I put onto a Barracuda steel front tri. Was one of my early framebuilding projects. Rides about as well as one would expect (I'd say wet noodle, but that cliche was already taken), which is to say, it's been hanging in the basement for nearly as long as I've lived in my current house. Point being, if you're interested in exploring replacement chainstays (or a very different kind of piece of mountain bike history), let me know.

  10. #10
    I'm just messing with you
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    Run a taut string from one dropout, around the headtube, back to other dropout. Now measure how far the string is from the seat tube.
    Chasing bears through the woods drunk with a dull hatchet is strongly not advised

  11. #11
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    Sealcove,

    here's 10 minutes of my time to give you a direct answer to your question...

    "The question is what to do at this point? Can the seat-stay/chain-stay be re-aligned without damaging the frame, especially since the frame material is aluminum? "

    At this point, what you need to do is get your frame to a builder with Aluminum fabrication and alignment experience. The frame needs to be placed on an alignment table to get a true indication of what is wrong.

    If the rear end is in fact out of alignment and it is within reasonable corrective tolerances, a dedicated fixture would then need to be produced to hold the rear triangle separately from the balance of the frame, supporting the weaker pivot connections, so that force may then be applied to correct the positioning. I would strongly recommend not aligning the rear end while it is attached to the front triangle, as the pivot points are not strong enough to withstand the necessary lateral forces without weakening.

    What can you expect to pay?

    I charge 120 bucks put a frame on the table and align if no significant repair/fabrication work is required. This includes total frame alignment and facing the hs and bb for re-assembly.

    If repair or custom fixturing is required, it's a shop rate of 60 bucks an hour.

    You'd probably be looking at another 3 hours of time for the dedicated fixturing, worse case scenario.

    To put some perspective to it, I've seen this frame sell on ebay in good shape for 2 bills. Like so many repairs or restorations, it comes down to your emotional attachment to the bike.

    What's it worth to you?

    cheers,

    rody

    PS... Info provided as an example, I DO NOT have time to perform the work, sorry.
    As requested by the MTBR gods, I am the voice of Groovy Cycleworks, check it out... http://www.groovycycleworks.com

  12. #12
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    Quote Originally Posted by Rody View Post
    Sealcove,
    At this point, what you need to do is get your frame to a builder with Aluminum fabrication and alignment experience. The frame needs to be placed on an alignment table to get a true indication of what is wrong.
    sorry.
    Some good news: Brion at Amp Research still has the alignment table and jigs to re-align the bike frame and is willing to perform the work, so I'm sending the frame out. It's been over a decade since they last sold frames, so it's good to know that they still support their products.

    I'll report the results when I get the frame back.

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