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  1. #1
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    Asymmetric chain tension

    So I have been trying to trouble shoot some pops and creaks in my drivetrain. I have replaced the cog, chain, and repacked the rear hub, so I think I can safely rule those out. I noticed last night that there is a pretty big difference in my chain tension depending on what part of the chainring/crank is on the top of the stroke cycle. As far as I can see the chainring is still perfectly round and my bolts are all tight.
    I'm guessing this is the reason for the noises I"m hearing (which occur at random and almost sound like the chain is catching on the cog and not coming off cleanly).

    I would guess the next step is a new bottom bracket?
    Anyone have any experience with this sort of problem?
    Thanks

  2. #2
    Old and Fixed, Moderator
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    It could be a variety of things.

    The obvious things to look at are the chainring, crankset and cog.

    I've found that true track rings, cogs, and hubs allow for a perfectly even tension. In addition to being stiffer, they are built to tighter tolerances( more round)..

    I had a similar issue with a Formula hub... I used a Phil Wood cog, Dura Ace 7600 cranks and rings... the cranks and cog came from another bike that had perfect tension but when I threaded the cog onto the Formula hub, I got an uneven tension.. My other sets of Formula hubs didn't have the same problem..

    What hubs and crankset/ring are you using?
    Dave Hickey/ Fort Worth

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  3. #3
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    Tha chainring may be round, but maybe the spider is not perfectly concentric. That's not uncommon, and it can cause the ring to be off-center. Usually there's enough play in the bolt holes to allow for some correction.

    Sheldon came up with a neat procedure for making this adjustment.
    http://www.sheldonbrown.com/fixed-co...n.html#tension

  4. #4
    wim
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    Quote Originally Posted by davemess
    I noticed last night that there is a pretty big difference in my chain tension depending on what part of the chainring/crank is on the top of the stroke cycle. A
    Very common with mid-level components. And as said by others, it's caused by very small manufacturing variations (aka tolerances). They're so small that you can't see them. These variations can be in the bottom bracket, crank spider, chainring, cog and rear hub. They can add up at one point in the crank circle, then cancel each other out at another point. One solution is to buy top-notch track components. But that would probably cost you much more than your entire bike did. Another one is the linked Sheldon Brown method of cancelling out variations, but that is tediuos and only gets you so far.

    The noises you hear are the typical noises of a tortured chain which is much too tight at one point in the crank circle. The quick (and, IMO, best) way to fix that is to adjust chain tension where it's just right at the tightest spot in the crank circle. That means, of course, that the chain will be a bit too loose at the loosest spot in the crank circle. But that's a lot better than crunching a super-tight chain over your chainwheel and sprocket once every crank revolution.

  5. #5
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    At first take, sounds like too much chain tension, which is exacerbated by an out of round chainring/crank spider.

    Try removing the chainring and rotating it one hole at a time around the spider, then install the chain again. You might find a location that works better.

    Some chainrings are just screwed up. I've had some that looked ok, but clearly caused more and then less chain tension as the crank rotates.

    If you have another chainring, try that. If it is then ok, you likely isolated the problem (the first ring), unless there is then a mysterious match between the second ring and the crank spider.

    Check chain line, too. A taught fixed chain will be much more susceptible to noise and grinding sounds if the chain line is off.

    Lube?

    Try running less tension, never so little that the chain becomes so slack that it might come off, but slack enough that it never binds.

    Remove the chain and see if the crank makes noises when you spin it.

    Quote Originally Posted by davemess
    So I have been trying to trouble shoot some pops and creaks in my drivetrain. I have replaced the cog, chain, and repacked the rear hub, so I think I can safely rule those out. I noticed last night that there is a pretty big difference in my chain tension depending on what part of the chainring/crank is on the top of the stroke cycle. As far as I can see the chainring is still perfectly round and my bolts are all tight.
    I'm guessing this is the reason for the noises I"m hearing (which occur at random and almost sound like the chain is catching on the cog and not coming off cleanly).

    I would guess the next step is a new bottom bracket?
    Anyone have any experience with this sort of problem?
    Thanks
    [SIGPIC][/SIGPIC]

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    Before I use it and lose my cool
    When I smile, tell me some bad news
    Before I laugh and act like a fool

  6. #6
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    Thanks for all the advice. So I finally got out and bought a new chainring, and when installing realized the rear wheel was suddenly out of true. So I went to true it,and realized the Bearings were pretty messed up (I had repacked it about a month ago, and apparently did a poor job).
    So one side was all kinds of messed up with misshapen bearings and discoloration. I thinking that the hub was most of the problem as the noises were almost unbearable today.
    So I am thinking I need to just take the wheel in to a shop and let them deal with it, I'm about out of patience.

    It is a Quando flip flop hub. Is there any way I can switch out the loose bearings for a cartridge? I leave in Portland now, and I'm sure the rain is doing a nice number on the bearings.

    I'm thinking the problems might have stemmed from the hub all along. The slightly off hub, would have lead to some of the chain tension issues (although I am still not completely ruling out the chainring, which is now replaced).

    All this is kind of frustrating to me, as my fixed is supposed to be my "simple", low maintenance bike.

  7. #7
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    Quote Originally Posted by davemess
    All this is kind of frustrating to me, as my fixed is supposed to be my "simple", low maintenance bike.
    Your bike is only as simple and low-maintenance as its components. Cartridge-bearing hubs, a cartridge bottom bracket, and a Chris King headset are the only way to go if you really want to avoid wrenching and rebuilding stuff all the time. Worth the investment, IMO, especially if you're dealing with Pac NW weather!

  8. #8
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    realized the Bearings were pretty messed up (I had repacked it about a month ago, and apparently did a poor job).
    So one side was all kinds of messed up with misshapen bearings and discoloration. I thinking that the hub was most of the problem as the noises were almost unbearable today.
    I suspect the causation flows the other way. Your excessive chain tension with the out-of-round ring wrecked your bearings.

    I don't live in quite as wet a place as you, but my rainy-day commuter fixie does fine with regular bearings. Overhaul is a 15-minute job, and I don't do it that often. But quality sealed bearings are nice, as others have said.

  9. #9
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    The chain was not really that tight, I would guess at it's tightest on the chainring, it was about the tension I would have wanted it to be run at. On the other sections of the chainring, most people would probably think it was too loose.

    So can I do cartridge bearings for this hub? Or do I just need a new hub to do that?

  10. #10
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    WEll, as I know most of you have been kept up at nights worrying about my bike problems. SO rest assured, I was able to repack the bearrings this morning and the noise was gone riding into work. Guess the hub was the problem all along. I did also get a new chainring, which seems to help with the tension issues as well.
    About how often should I be looking to repack the bearrings? Just wait until they start making noises again?

  11. #11
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    packing

    Quote Originally Posted by davemess
    About how often should I be looking to repack the bearrings? Just wait until they start making noises again?
    Loose bearings I'd repack about once a year, but check them anytime you've been through some serious rain and puddles.
    [SIGPIC][/SIGPIC]

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  12. #12
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    So every day....... (I live in Portland)

    Thanks

  13. #13
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    oh my

    Quote Originally Posted by davemess
    So every day....... (I live in Portland)

    Thanks
    I feel for you.

    I would run sealed cartridge bearings there.
    [SIGPIC][/SIGPIC]

    When my fist clenches, crack it open
    Before I use it and lose my cool
    When I smile, tell me some bad news
    Before I laugh and act like a fool

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