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  1. #1
    Senior Member fenester's Avatar
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    Adjusting chainring / imperfect chainring

    Greetings All,

    My question relates to my SS/FG bicycle. I noticed that at one point in the crank/chainring rotation the chain is much tighter (when the drive-side crank is at 3 o'clock when viewed from drive-side). Result is that when I adjust the rear-wheel accordingly, the chain is really (dangerously) loose when the crank is rotated 180 from that position.

    [Sugino cranks, Rocket Ring 46t, Surly freewheel 18t]

    I tried SB's suggestion/method of loosening all the chainring bolts and tapping/bouncing tool (15mm wrench) on chain to nudge it into position to compensate for the imperfection in the chainring. So I tried really squeezing the chain together, thinking the chainring might just be a little stuck. Still didn't help, the chain remained very tight/very loose.

    So, my question(s):

    Did I miss something? Any suggestions before I buy a new chainring? (the current chainring and whole bike only have about 200 miles on them)

    I've gleened that chainrings often aren't truly circular, but this seems extreme to me. [edit: I'm reasonably sure it's not the freewheel because the tightening/loosening of the chain occurs at the same point on every rotation of the cranks...but feel free to correct me on that.]

    Thanks for your suggestions and comments!
    Last edited by fenester; 01-19-07 at 08:56 AM.
    "Mobility without effort constitutes a kind of unreal happiness, a suspension of existence, an irresponsibility."

  2. #2
    Senior Member
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    Sounds like you've got a Biopace(ovoid) ring there--no good for a fixie. A standard ring will solve all your problems (well, the chain related ones anyway).

  3. #3
    Senior Member fenester's Avatar
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    Hi, thanks for the reply.
    I'm reasonably sure it's not biopace. As far as I know Rocket Rings are made for BMX/singlespeed and supposed to be more or less circular.
    "Mobility without effort constitutes a kind of unreal happiness, a suspension of existence, an irresponsibility."

  4. #4
    Newbie
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    tight spot in the chain

    You might try changing the orientation of the ring in relation to the cranks... i.e. shift over a bolthole or two.

    Does the ring wobble if you look at its position re: the chainstay? This would suggest a bent ring, a bent crankarm spider, or a bent BB spindle. It's a long shot but I've seen a bent spindle create a tight spot, and flipping the arms on the spindle by 180 degrees solved it. (This was with a used arm & spindle that took a hit together.)

    Good luck.

  5. #5
    Grumpy Old Bugga europa's Avatar
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    Sure it's not the chain itself? A tight spot in the chain is often a symptom of a worn chain or a new chain with a couple of tight sideplates (can be loosened by flexing the chain side to side at that point).

    Richard
    I always look for the cheap options first
    I had a good bike ... so I FIXED it

  6. #6
    cab horn
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    Quote Originally Posted by xlrogue
    Sounds like you've got a Biopace(ovoid) ring there--no good for a fixie. A standard ring will solve all your problems (well, the chain related ones anyway).
    Fear mongering. Biopace works fine on fixed gears.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  7. #7
    Senior Member fenester's Avatar
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    Ok,
    I checked for horizontal "wobble" on the chainring by sighting down it from above, it looks straight. Also, it's not just that the chain binds a little in the "tight" position, the chain tension gets tight at that point (when checked by pressing vertically on the chain between chainring and cog), so I don't think it's the links.

    Unfortunately I don't have a spare chainring to troubleshoot with, but I'm going to my LBS tonight so I'll see if they have one I can throw on quick just to check. I'm with you, better to check for the cheap fix first. (I haven't had a chance yet to rotate the chainring on the cranks yet, but will check it before buying new one)

    I'll post back with results when I get it fixed

    Thanks again,
    fen.
    "Mobility without effort constitutes a kind of unreal happiness, a suspension of existence, an irresponsibility."

  8. #8
    Senior Member meatwad's Avatar
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    Although unlikely it could be due to uneven wear on the spindle. However it would display horizontal deflection.I would move the chainring to different bolt holes and see what happens.

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