Chain tension varies as I turn crank. Possible causes?- Mtbr.com
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  1. #1
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    Chain tension varies as I turn crank. Possible causes?

    Any ideas what might be causing that? My first thought was maybe a bent chain ring(or cog), but I don't see anything obvious.

  2. #2
    Let's ride
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    is your CR a center spline type, or 4-5bolt setup?
    If 4-5 bolt, try loosening all the CR bolts and then spin the crank a few times and see if the tension issue has changed? If not enough, rotate your CR on the crank 1 bolt hole and try test again. Once you're happy with the tension issue, tighten the CR bolts. See that the tension issue hasn't changed for the worse.

    If it is a cinch type, old xtr, etc, you can still rotate the CR about the shaft and see if that changes for the better.

    The same can be true for your cog, but typically we look at the CR first.

    Good luck.

  3. #3
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    It's a 4 bolt Raceface narrow wide ring. I also wondered if the varying tension might be something related to it being a narrow wide. This is my first experience with one of those.

  4. #4
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    Is it getting loose enough to drop the chain? If not, don't worry about it. If so, it's probably the ring not being perfectly round, try Rensho's suggestions and if that doesn't work buy a new ring.

    BTW, why are you running N/W on a singlespeed?

    -Walt

  5. #5
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    Chains also develop stretched out sections. I find that most of mine are tighter/looser depending on where in the pedal stroke I am.

  6. #6
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    All single speeds do that to some degree and it's almost always due to an imperfectly centered chainring, sometimes the method rensho mentioned can work but a sometimes there's not much you can do about it.

  7. #7
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    I'll try rotating the ring and see if that helps. I've had the ring off and may not have put it back on in exactly the same position.

    Ring and chain are both pretty new so I don't think it's a wear issue. I'm using a narrow wide because that's what the Trek Superfly SS comes with. I switched the cog yesterday, so it's also possible I may not gotten something quite right when tinkering around with the bike. Might have had varying tension even before and I just hadn't noticed it. It's not loose enough to drop the chain.

  8. #8
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    I've never had a single speed where the chain had equal tension as you turned the crank. I just adjust the chain tension based on the tightest section of chain. Never been a problem.

  9. #9
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    Thanks for the info and advice, everyone. Rotating the ring seems to have made the differing tension a bit less apparent.

    I checked my Kona Unit to see if the tension varies, and yeah, it does, too. I think the difference is that I have the chain tension higher overall on my Superfly, and that makes the high tension part of the circuit much more noticeable. I may adjust the sliders a bit.

  10. #10
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    Spineless chainrings can be pretty round. But I run an oval and have a little up and down on my chain - but it never drops. Chainline is key.

  11. #11
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    Ya, don't worry about it. As long as the chain tension is good through out the pedal stroke.

    Worrying about this, is like worrying about your stem being perfectly aligned with your front tire.


  12. #12
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    Quote Originally Posted by wjphillips View Post
    Worrying about this, is like worrying about your stem being perfectly aligned with your front tire.
    Did this last night and said to myself how much I hate trying to line up a stem and front tire.
    "Lock S-Foils in attack position"

  13. #13
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    Quote Originally Posted by Rogueldr View Post
    Did this last night and said to myself how much I hate trying to line up a stem and front tire.
    I have literally NEVER gotten that right on the first try. I can spend a bunch of time fiddling, but then after 5 minutes on the trail... crap, I realize it's not straight.

    Then again I raced a national after a crash in the first 30 seconds with the bars off by 25 degrees or so, and got so used to it that it felt weird for a few minutes when I fixed it at the finish and rode back to my hotel.

    -Walt

  14. #14
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    Quote Originally Posted by khardrunner14 View Post
    Chains also develop stretched out sections. I find that most of mine are tighter/looser depending on where in the pedal stroke I am.
    I bet if you watched your chain as you turn the crank, say when your lubing the chain, you'll see that the chain does not perfectly align with the crank rotation so it's impossible to form tighter or looser spots. Keep an eye on the powerlink, or if you don't have one mark one link somehow.

    Tight/loose spots are most certainly from off-center chainring which is nearly impossible to get perfectly aligned for even chain tension.

    I have found that running a larger chainring seems to help a bit. I switched to 34-21 from 32-20 and notice less variation in chain tension.




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  15. #15
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    This is Sheldon Brown's trick:

    Centering Chainwheels

    The chain tension on a fixed gear is quite critical, and is regulated by moving the rear axle back and forth in the forkends. If the chain is too tight, the drivetrain will bind, perhaps only at one angle of the pedals (chainwheels are not usually perfectly concentric). It should be tight as it can be without binding. If the chain is too loose, it can fall off, which is quite dangerous on a fixed gear.

    Set the rear axle so that the chain pulls taut at the tightest part of the cranks' rotation. One at a time, loosen up each of the stack bolts, and tighten it back just finger tight. Spin the crank slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chain ring move a bit on its spider. Then rotate the crank some more, finding the new tightest spot, and repeat as necessary.

    This takes a little bit of your hands' learning how hard to hit the chain, and how loose to set the stack bolts, but it is really quite easy to learn.

    Tighten up the stack bolts a bit and re-check. Tighten the stack bolts in a regular pattern, like the lug nuts on a car wheel. My standard pattern is to start by tightening the bolt opposite the crank, then move clockwise 2 bolts (144 degrees), tighten that one, clockwise 2 more, and so on. Never tighten two neighboring bolts in a row. You may prefer to go counterclockwise, but try to get in the habit of always starting at the same place and always going the same way. This reduces the chances of accidentally missing a bolt.

    Once you have the chainrings centered and secured, adjust the position of the rear axle to make the chain as nearly tight as possible without binding. Notice how freely the drive train turns when the chain is too loose. That is how freely it should turn when you are done, but with as little chain droop as possible.

  16. #16
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    Quote Originally Posted by have2ride2day View Post
    This is Sheldon Brown's trick:

    Set the rear axle so that the chain pulls taut at the tightest part of the cranks' rotation. One at a time, loosen up each of the stack bolts, and tighten it back just finger tight. Spin the crank slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chain ring move a bit on its spider. Then rotate the crank some more, finding the new tightest spot, and repeat as necessary.
    ...
    Tighten up the stack bolts a bit and re-check. ...
    That has always got me close enough, so far. I haven't bothered trying to make it perfect.

    "it IS possible that you are faster or slower than anybody else who is having at least as much if not more or less fun"

  17. #17
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    Quote Originally Posted by have2ride2day View Post
    This is Sheldon Brown's trick:
    Thanks for that, but I think I'm going to leave well enough alone. The slots in the nuts that Raceface provides to secure the chain ring bolts look like they'd be pretty easy to strip out, so I'd rather mess with them as little as possible.

    I'll keep the Sheldon Brown method in mind the next time I need to install a chain ring.

  18. #18
    xhx
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    Any advice for centering a chainring on a hidden bolt crankset? I'm using a SRAM Force & one of the bolts is behind the crank arm. Pain in the a$$. Alternately if anyone knows where to get a 5 arm 110 BCD spider with all 5 bolts in the normal places you'll be my hero.

  19. #19
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    I had this issue once when I used the wrong power link on the wrong chain. 9 speed link on 8 speed chain I think.

    Sent from my LG-D850 using Tapatalk

  20. #20
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    Quote Originally Posted by Walt View Post
    Is it getting loose enough to drop the chain? If not, don't worry about it. If so, it's probably the ring not being perfectly round, try Rensho's suggestions and if that doesn't work buy a new ring.

    BTW, why are you running N/W on a singlespeed?

    -Walt
    I run one on mine. Seems to help if my chain is too loose on a real chattery trail.

    Sent from my LG-D850 using Tapatalk

  21. #21
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    Quote Originally Posted by Geralt View Post
    I'll try rotating the ring and see if that helps. I've had the ring off and may not have put it back on in exactly the same position.

    Ring and chain are both pretty new so I don't think it's a wear issue. I'm using a narrow wide because that's what the Trek Superfly SS comes with. I switched the cog yesterday, so it's also possible I may not gotten something quite right when tinkering around with the bike. Might have had varying tension even before and I just hadn't noticed it. It's not loose enough to drop the chain.
    Did you check the cog if it was properly (ie centred) machined? I had one that had the mounting spines off-centre, worked like an eccentric... Emailed Point (cheapo cog) and they posted me a new one.

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