Chain tightens, then loosens; What's up?

Discussion in 'Cycling Equipment' started by Joe, Apr 9, 2003.

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  1. Joe

    Joe Guest

    Hey,

    I'm new to the sport of BMX. I got a new bike (DK Dayton), but notice that the chain tightens and
    loosens as the pedals spin. I called the bike shop that I got the bike from, and they suggested a
    new chain. The bike's brand-new, so it's not as though I have been beating on it. Can I just
    continue riding the bike and get the chain stretched out so it spins through smoothly?

    Also, I would assume that I should tighten the chain while the pedals are in the 'loose stage'. The
    chain will get rather tight while I spin through the tight phase though, will that damage anything?

    Thanks...
     
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  2. Gary Smiley

    Gary Smiley Guest

    Your front chainring is not round, and is probably eliptical. Tighten the chain while the pedals are
    in the tight stage. If you tighten the chain while the pedals are in the loose stage, when you pedal
    around to the tight stage, the chain will be too tight, and could break at that point.

    joe wrote:

    > Hey,
    >
    > I'm new to the sport of BMX. I got a new bike (DK Dayton), but notice that the chain tightens and
    > loosens as the pedals spin. I called the bike shop that I got the bike from, and they suggested a
    > new chain. The bike's brand-new, so it's not as though I have been beating on it. Can I just
    > continue riding the bike and get the chain stretched out so it spins through smoothly?
    >
    > Also, I would assume that I should tighten the chain while the pedals are in the 'loose stage'.
    > The chain will get rather tight while I spin through the tight phase though, will that damage
    > anything?
    >
    > Thanks...
     
  3. Michael Dart

    Michael Dart Guest

    "joe" <[email protected]> wrote in message news:[email protected]...
    > Hey,
    >
    > I'm new to the sport of BMX. I got a new bike (DK Dayton), but notice that the chain tightens and
    > loosens as the pedals spin. I called the bike shop that I got the bike from, and they suggested a
    > new chain. The bike's brand-new, so it's not as though I have been beating on it. Can I just
    > continue riding the bike and get the chain stretched out so it spins
    through
    > smoothly?
    >
    > Also, I would assume that I should tighten the chain while the pedals are
    in
    > the 'loose stage'. The chain will get rather tight while I spin through
    the
    > tight phase though, will that damage anything?
    >
    > Thanks...
    >
    >

    Bent crank or bb axle? Hold a pencil against the frame pointing at the chainring as a reference and
    see if it 'wobbles' when you turn the crank.

    Mike
     
  4. Matt O'Toole

    Matt O'Toole Guest

    "joe" <[email protected]> wrote in message news:[email protected]...

    > I'm new to the sport of BMX. I got a new bike (DK Dayton),
    but notice that
    > the chain tightens and loosens as the pedals spin. I
    called the bike shop
    > that I got the bike from, and they suggested a new chain.
    The bike's
    > brand-new, so it's not as though I have been beating on
    it. Can I just
    > continue riding the bike and get the chain stretched out
    so it spins through
    > smoothly?
    >
    > Also, I would assume that I should tighten the chain while
    the pedals are in
    > the 'loose stage'. The chain will get rather tight while I
    spin through the
    > tight phase though, will that damage anything?

    I'm not exactly sure what you're talking about, but it sounds like your chainring might not be
    perfectly centered. This problem comes up sometimes with fixed gear bikes. The solution is to loosen
    the chainring bolts until they're just tight enough to hold, but loose enough that the chainring can
    be tapped back and forth with a hammer for adjustment. Then turn the cranks slowly, and as the chain
    gets tighter, tap the chainring back a little. By doing this several times, you can eventually get
    the chainring perfectly centered. Not all chainrings can be adjusted this way, though. In fact, this
    procedure can be a real pain. You might go back to the shop, suggesting this is the problem, and see
    what they have to say. Maybe some others here will have some other ideas too.

    Matt O.
     
  5. joe wrote:
    > Hey,
    >
    > I'm new to the sport of BMX. I got a new bike (DK Dayton), but notice that the chain tightens and
    > loosens as the pedals spin. I called the bike shop that I got the bike from, and they suggested a
    > new chain. The bike's brand-new, so it's not as though I have been beating on it.

    A certain amount of out-of-roundness of the chainring is not unusual, especially on less expensive
    cranksets. Sometimes you can adjust it a bit, as described at:

    http://sheldonbrown.com/fixed-conversion.html#tension

    > Can I just continue riding the bike and get the chain stretched out so it spins through smoothly?

    It's unlikely that this has anything to do with the chain, rather that the chainring is not
    perfectly centered.

    > Also, I would assume that I should tighten the chain while the pedals are in the 'loose stage'.
    > The chain will get rather tight while I spin through the tight phase though, will that damage
    > anything?

    Yes, it will. Set it so that even at the tightest position, it shouldn't bind.

    Sheldon "Sometimes Eccentricity Is Bad" Brown +----------------------------------------------+
    | My mind is aglow with whirling, transient | nodes of thought careening through a cosmic | vapor
    | of invention! --Mel Brooks |
    +----------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
    617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
    http://captainbike.com http://sheldonbrown.com
     
  6. Cy Galley

    Cy Galley Guest

    Is the pedal chain ring marked Bio-Pace?

    "Sheldon Brown" <[email protected]> wrote in message
    news:[email protected]...
    >
    >
    > joe wrote:
    > > Hey,
    > >
    > > I'm new to the sport of BMX. I got a new bike (DK Dayton), but notice
    that
    > > the chain tightens and loosens as the pedals spin. I called the bike
    shop
    > > that I got the bike from, and they suggested a new chain. The bike's brand-new, so it's not as
    > > though I have been beating on it.
    >
    > A certain amount of out-of-roundness of the chainring is not unusual, especially on less expensive
    > cranksets. Sometimes you can adjust it a bit, as described at:
    >
    > http://sheldonbrown.com/fixed-conversion.html#tension
    >
    > > Can I just continue riding the bike and get the chain stretched out so it spins
    through
    > > smoothly?
    >
    > It's unlikely that this has anything to do with the chain, rather that the chainring is not
    > perfectly centered.
    >
    > > Also, I would assume that I should tighten the chain while the pedals
    are in
    > > the 'loose stage'. The chain will get rather tight while I spin through
    the
    > > tight phase though, will that damage anything?
    >
    > Yes, it will. Set it so that even at the tightest position, it shouldn't bind.
    >
    > Sheldon "Sometimes Eccentricity Is Bad" Brown +----------------------------------------------+
    > | My mind is aglow with whirling, transient | nodes of thought careening through a cosmic | vapor
    > | of invention! --Mel Brooks |
    > +----------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
    > 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
    > http://captainbike.com http://sheldonbrown.com
     
  7. Joe

    Joe Guest

    I took a few photos of the chain ring area to let you guys know what exactly I'm talking about.

    http://www.geocities.com/boardmethod/photos.html

    I stuck a small gum eraser on the chainstay and pressed it into shape next to the chain ring. I then
    spun the chain ring around to see if it was more oval the circular. The chain ring rubbed the eraser
    quite smoothly the whole way through. It appears to be quite circular. I then pressed the eraser
    closer to the chain ring, so when spun, the chain ring left a mark on the eraser. The indent made on
    the eraser was quite narrow. This would seem to mean the that chain ring is quite solid and true.
    While the chain was off, I spun the freewheel. It didn't appear to wobble around at all.

    I am starting to wonder if indeed the chain is bad. It is a KMC brand. The tension of the chain does
    vary quite dramatically. When I have the time, I could take a shot of the chain in the tight stage,
    and then in the loose stage.

    What do you think? Replace the chain?
     
  8. A Muzi

    A Muzi Guest

    "joe" <[email protected]> wrote in message news:[email protected]...
    > Hey,
    >
    > I'm new to the sport of BMX. I got a new bike (DK Dayton), but notice that the chain tightens and
    > loosens as the pedals spin. I called the bike shop that I got the bike from, and they suggested a
    > new chain. The bike's brand-new, so it's not as though I have been beating on it. Can I just
    > continue riding the bike and get the chain stretched out so it spins
    through
    > smoothly?
    >
    > Also, I would assume that I should tighten the chain while the pedals are
    in
    > the 'loose stage'. The chain will get rather tight while I spin through
    the
    > tight phase though, will that damage anything?
    >
    > Thanks...
    >
    >

    All the components of the system, while relatively round, are imperfect. When you spin the crank
    around you show the errors of roundness in all the various parts of the crank bearing assembly and
    the rear hub/freewheel. This is normal although the amount of variance is less with better-quality
    equipment.

    Set your chain so the tight spot is such that you can still deflect the chain a half inch with
    a light finger pressure. Overtightening the chain as you suggest will very quickly eat up all
    the various bearing assemblies. Err slightly to the loose side, not the tight side, of perfect
    chain tension.

    Since the bicycle is new, perhaps you might ask the dealer to revisit that adjustment?

    --
    Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
     
  9. joe wrote:
    > I took a few photos of the chain ring area to let you guys know what ex=
    actly
    > I'm talking about.
    >=20
    > http://www.geocities.com/boardmethod/photos.html
    >=20
    > I stuck a small gum eraser on the chainstay and pressed it into shape n=
    ext
    > to the chain ring. I then spun the chain ring around to see if it was m=
    ore
    > oval the circular. The chain ring rubbed the eraser quite smoothly the =
    whole
    > way through. It appears to be quite circular. I then pressed the eraser=

    > closer to the chain ring, so when spun, the chain ring left a mark on t=
    he
    > eraser. The indent made on the eraser was quite narrow. This would seem=
    to
    > mean the that chain ring is quite solid and true. While the chain was o=
    ff, I
    > spun the freewheel. It didn't appear to wobble around at all.
    >=20
    > I am starting to wonder if indeed the chain is bad. It is a KMC brand. =
    The
    > tension of the chain does vary quite dramatically. When I have the time=
    , I
    > could take a shot of the chain in the tight stage, and then in the loos=
    e
    > stage.
    >=20
    > What do you think? Replace the chain?

    As I said before, it's unlikely it's the chain. Probably the chainwheel =

    or rear sprocket is not perfectly centered.

    Make a note of where the cranks are pointing when the chain is at its=20 tightest. The give the
    cranks a turn and see if it gets tight again=20 with the cranks in the same orientation. If it is
    consistently tight at =

    a particular angle of the cranks, the problem is in the crank, chainring =

    or possibly bottom bracket.

    If the tightness occurs at different crank orientations, it's probably=20 the rear cog or hub. Cheap
    track sprockets (and, occasionally, even=20 fairly expensive ones are sometimes out of round.

    It's also possible that _both_ sprockets are out of round by small=20 amounts, and that when they
    _both_ line up facing in opposite=20 directions, that's when the chain gets tight.

    Sheldon "Not So Tight It Binds, Not So Loose It Can Fall Off" Brown
    +----------------------------------------+
    | I never did a day=92s work in my life; | it was all fun. --Thomas Edison |
    +----------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
    617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
    http://captainbike.com http://sheldonbrown.com
     
  10. Ant

    Ant Guest

    "joe" <[email protected]> wrote in message

    > I am starting to wonder if indeed the chain is bad. It is a KMC brand. The tension of the chain
    > does vary quite dramatically. When I have the time, I could take a shot of the chain in the tight
    > stage, and then in the loose stage.

    Dude, ill bet money it ain't the chain. have you checked the archives? peruse
    http://tinyurl.com/9a6o. many people have asked this before. there are many answers.

    cheers
     
  11. Bikefixr

    Bikefixr Guest

    REAL common on singles like BMX. The front chainring hole is probabally a bit off-center. Find the
    medium between the loose and tight, adjust to that. The chain will stratch a bit and it'll run
    smooth. The problem is NOT the chain. Amazes me to this day how stupid some shops have become.
     
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