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  1. #1
    mtbr member
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    Evil Chain suck with Stumpjumper FSR

    Hey folks,

    I have a lousy problem with chain suck with my 05 FSR Expert. Doesn't happen often but typically in long races or events (per Murphy's Law). The problem is that not only does the chain get sucked in....it stays in...jammed in there good. During my last event it happened several times. Each time it took several guys around 10 minutes to free the chain using multiple tools. The attached pics illustrate the last occurance. And yes, my chain is quite dirty in the pics. But it's happened several times with a brand new chain (clean and lubed). And my chain ring wasn't worn. There's a good technical write-up on chain suck here:
    http://www.fagan.co.za/Bikes/Csuck/

    But more to the point, as you can see from the pics, it seems like faulty design. Almost as if the Specialized engineers deliberately designed the frame and chainring fasteners (hex bolts) to capture the chain and jam it in good. That shiny beveled groove on the frame has the precise geometry to capture a chain and jam it beneath the fasteners on the small chainring. A few thousanths deeper or shallower and there would be no problem. And the fasteners have an insidious right-angled edge on them. Just high enough to allow the chain to slip beneath the square edge and jam it in. Bravo, you evil bike engineers!

    I don't mind occasional chain suck (a rare enough occurance) as long as it doesn't take 10 minutes and several tools to unjam the chain. One simple solution would be to find fasteners with smooth, mushroom shaped tops/edges. Or grind them down. This way after getting sucked the chain will simply slip out and you're up and running in seconds. No special tools required and no cussing and swearing. Another solution would be to grind that beveled groove on the frame to deepen it and/or smooth out the edge. Or eliminate it with Bondo or fiberglass and epoxy.

    I've seen the Ronnie Ring, BTW. Looks cool but it doesn't seem ideal since it adds weight and seems like a band-aid approach. I'd rather fix the source of the jamming problem.

    I have a race coming up and I'm getting concerned. Suggestions?
    Attached Images Attached Images

  2. #2
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    Assuming I'm looking at the pictures correctly:

    Given that it's disengaging to the inside of the small chainring, I'd see if an "AJ's Frameguard" can fit on your frame. I use one of these to prevent the chain from falling off to the inside of the small ring, and it COMPLETELY solves this issue. Your situation is a bit different, but based on the pictures, it looks like this could potentially solve your issue.

    Here is the site: http://www.ajsbikeparts.com/web-AJBIKEPARTs/AJ's%20Frameguard.htm

    Larry

  3. #3
    thecentralscrutinizer
    Reputation: mopartodd's Avatar
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    Keeping your drivetrain clean would help a bunch. That's nasty.
    2015 Kona JTS
    2014 Giant Anthem 27.5
    2013 DeVinci Leo SL
    2009 SE Racing SoCal Flyer
    2008 SE lil Ripper
    2003 TiSport Gman

  4. #4
    Master of None
    Reputation: presslab's Avatar
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    Looks like it's falling off the top of the chainring and getting jammed up, which is not the classic definition of chainsuck.

    Try a N-Gear jump stop.
    http://gvtc.com/~ngear/
    http://gvtc.com/~ngear/chainsuck.html

  5. #5
    mtbr member
    Reputation: konut's Avatar
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    could be your chain is to long also,and maybe try new chainring bolts.

    another idea could be that your running granny ring and small gears on the back which doesn't help.

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