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Thread: Wobbly Crank

  1. #1
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    Wobbly Crank

    The bike I’ve got is almost new, but the other day I noticed that the crank has developed a bit of play in it and today it has gotten more so.

    When you wobble one of the pedals the other one moves so I wouldn’t have thought that the mettle bit in the centre has broke.

    Is it just the case that it needs tightening?
    Also the bottom of the crank seems oily so maybe oil has leaked out as well.

  2. #2
    Old Fogy
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    Take it back where you bought it and have them check it.

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    I got it of the internet last summer

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    Senior Member bigvegan's Avatar
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    It sounds like you your bottom bracket is out of whack.

    Find an LBS/bike co-op you can trust and see if it can be adjusted, or if it needs replacement.

    The "metal bit in the center" (aka the spindle / axle) may not have broken, but if the bearings have come apart or worn out, that's going to need some fixing/adjusting.

    Depending on the age of the bike, it's either a sealed bottom bracket or a "cup and cone" bottom bracket.


    (example of cup and cone bottom bracket)


    (example of sealed bottom bracket)


    If it's sealed, you buy a new one for $25 or so, and pay a few more $ to have it installed. I it's cup and cone, it can be rebuilt pretty easily, probably for about the same price (fewer parts, but more labor.)

    If there's a bike co-op/collective, you can probably bring it in there and have them show you how to adjust it (if it's a cup and cone BB - http://www.sheldonbrown.com/tooltips/bbadj.html), or put a new sealed BB in if you want to do it yourself instead of paying the shop.

    Those are all assuming it's a 3 piece crankset. If it's a one-piece (Ashtabula) crankset, it will be similar to a cup and cone BB, except that the cranks/spindle are all 1 piece.

    (After re-reading your post, I'm guessing you're posting from the other side of the Atlantic, so my pricing may be worthless to you, and you probably don't have an Ashtabula crank, as those were mostly American.)

    Good Luck!

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    Great State of Varmint Panthers007's Avatar
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    Unless you are a good bike-mechanic, this is another good reason not to purchase bicycles off the internet or a catalog. I hope you have a good bike-shop or collective nearby as stated above. Please don't ride it if you can help it until it's fixed.

    Good Luck!
    How do you keep an idiot in suspense?

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    Perhaps the crankarm is just loose on the spindle? This can quickly cause damage to the crankarm, so I agree with the other about (a) not riding it until it's fixed and (b) taking it to a LBS or experienced mechanic. They should be able to sort out what's wrong very quickly.

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    cab horn
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    Quote Originally Posted by Mondoman View Post
    Perhaps the crankarm is just loose on the spindle? This can quickly cause damage to the crankarm, so I agree with the other about (a) not riding it until it's fixed and (b) taking it to a LBS or experienced mechanic. They should be able to sort out what's wrong very quickly.
    Not if the other crank arm moves along with it. Like the Op said.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

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    It's not clear to me that the OP meant that the other crank moves *exactly* as much as the first crank. Regardless, an experienced mechanic able to fiddle with it in person will be able to quickly sort it out.

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    Quote Originally Posted by bigvegan View Post
    It sounds like you your bottom bracket is out of whack.

    Find an LBS/bike co-op you can trust and see if it can be adjusted, or if it needs replacement.

    The "metal bit in the center" (aka the spindle / axle) may not have broken, but if the bearings have come apart or worn out, that's going to need some fixing/adjusting.

    Depending on the age of the bike, it's either a sealed bottom bracket or a "cup and cone" bottom bracket.


    (example of cup and cone bottom bracket)


    (example of sealed bottom bracket)


    If it's sealed, you buy a new one for $25 or so, and pay a few more $ to have it installed. I it's cup and cone, it can be rebuilt pretty easily, probably for about the same price (fewer parts, but more labor.)

    If there's a bike co-op/collective, you can probably bring it in there and have them show you how to adjust it (if it's a cup and cone BB - http://www.sheldonbrown.com/tooltips/bbadj.html), or put a new sealed BB in if you want to do it yourself instead of paying the shop.

    Those are all assuming it's a 3 piece crankset. If it's a one-piece (Ashtabula) crankset, it will be similar to a cup and cone BB, except that the cranks/spindle are all 1 piece.

    (After re-reading your post, I'm guessing you're posting from the other side of the Atlantic, so my pricing may be worthless to you, and you probably don't have an Ashtabula crank, as those were mostly American.)

    Good Luck!
    Hay,
    Beach bikes (who I bought it from) said that the manufacturer (firmstrong) will replace the part.

    What is it that you think I actually need to ask them to replace?
    On the specs it says that the crankset is a Forged One Piece, 48T

    And you are right bigvegan, I am from the other side of the Atlantic, but am in the US at the moment, so your pricing is definitely of use, thanks.

    Mondoman; it does seem as though the pedals do seem to move as much as one another.

    The thing is the bike has less than one hundred miles on it, maybe it got damaged when it fell over in the garage a couple of times.

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    Just for reassurance while you are waiting to get it repaired, if wiggling one crank causes the other crank to wiggle just as much, there is probably no serious damage. Likely one or both bottom bracket cups have come loose which frequently happens if the mechanic/assemblydroid didn't use just the right amount of differential muscle on the two sides when installing them. Likely nothing at all needs to be replaced, just tightened up properly.

    If one crank can be wiggled, even a tiny little bit in any direction, where it joins "the mettle bit in the centre" [the spindle] even while you grasp the other crank firmly to hold it still, then the crank has loosened on the spindle and can get irreversibly damaged very quickly. But a mechanic can tell even quicker what has happened.

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    Senior Member bigvegan's Avatar
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    "What is it that you think I actually need to ask them to replace?
    On the specs it says that the crankset is a Forged One Piece, 48T"

    Wow, so it is a 1 piece / Ashtabula crankset. You need to have them check the bearings and re-tighten/adjust everything for you, and replace bearings/cups as necessary.

    They're pretty rebuildable, so it may just need some adjusting/tightening instead of a whole new crankset.

    http://www.sheldonbrown.com/opc.html - Here's some more info one one piece cranks.

    Hope you're enjoying your time in the states.

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    I tightened the bolt thing that goes around the peddle shaft as it enters the spindle and that seems to have solved it. I only did the one on the left hand side as the one on the right hand side I can’t get to, but in ether case it all seems fine now.

    And bigvegan you seem shocked by my one piece crank. I heard that 3 piece cranks are much better. And even before this incident I considered getting one. Would I notice a difference in speed?

    And thanks I am enjoying myself here. I always wanted a beach cruiser.

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    Quote Originally Posted by Ruthy View Post
    I tightened the bolt thing that goes around [emphasis added] the peddle shaft as it enters the spindle and that seems to have solved it. ... it all seems fine now.
    Hmmm, are we maybe now talking about a 3-piece cottered crankset???

    Ruthy, the "bolt thing" that you tightened, is it:
    1) a little nut (9 or 10 mm) mounted on what looks like a bolt that goes right through the "peddle (pedal) shaft" [crank] and out the other side, perpendicular to the spindle and not into it?

    or is it:
    2) a big bolt (13 or 14 mm) that sits inside the very end of the crank and screws directly into the spindle?

    What kind of tool did you use to tighten it?

    Edit: Note that "Forged One Piece" could mean just that the crank arm together with the "spider" (the "spokes" the that chainrings bolt to) is forged from one piece of metal, rather than being two pieces swaged together as on cheap and nasty ones.

    Les
    Last edited by conspiratemus; 03-07-09 at 09:12 AM.

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    Morning Les

    It’s a big bolt (at least 14mm, probably a bit more) that seems to screw straight into the spindle.

    I used adjustable grips to tighten it.

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    ^^Ah, OK, not a cottered crank then.
    You really need a hexagonal socket to tighten those bolts down pretty tight to press the crank firmly onto the spindle so it won't wiggle loose again. A socket will engage all six flats on the bolt and allow you to turn it with the required force without slipping off and marring the bolt. Bike shops sell wrenches (spanners, I think you call them in the U.K.) made just for this purpose. But if you have a set of sockets with a ratchet driver, the 13 or 14 mm socket will often work. Only trouble is, often the walls of the socket from the ratchet set will be too thick to allow the socket to slip down into the cavity in the crank to grab the bolt.

    As other posters have mentioned, when a crank comes loose like this, the steel spindle often damages the square hole in the crank so that it will not stay tight, or continues to wiggle even when the big bolt is tightened up fully. Then you need a new crank.

    First lesson in Mechanics 101: Never use any kind of grips (pliers) on a nut or bolt. They'll ruin it so that a proper wrench (spanner) will not fit to do the job right.

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    I borrowed the right tools, and think its all fine now.
    Your right they are called spanners in England. I didn’t know, when I came to the US on previous occasions, that they were called something different here, and people didn’t seem to know what I was on about.

    After asking around, from what I gather fitting a three piece crank wouldn’t really make too much difference.

    And thanks for your help Les, and everyone one else who helped out.

  17. #17
    Senior Member badmother's Avatar
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    Quote Originally Posted by conspiratemus View Post
    ^^Ah, OK, not a cottered crank then.
    You really need a hexagonal socket to tighten those bolts down pretty tight to press the crank firmly onto the spindle so it won't wiggle loose again. A socket will engage all six flats on the bolt and allow you to turn it with the required force without slipping off and marring the bolt. Bike shops sell wrenches (spanners, I think you call them in the U.K.) made just for this purpose. But if you have a set of sockets with a ratchet driver, the 13 or 14 mm socket will often work. Only trouble is, often the walls of the socket from the ratchet set will be too thick to allow the socket to slip down into the cavity in the crank to grab the bolt.

    As other posters have mentioned, when a crank comes loose like this, the steel spindle often damages the square hole in the crank so that it will not stay tight, or continues to wiggle even when the big bolt is tightened up fully. Then you need a new crank.

    First lesson in Mechanics 101: Never use any kind of grips (pliers) on a nut or bolt. They'll ruin it so that a proper wrench (spanner) will not fit to do the job right.
    Read again: It is a ONE PIECE (crank arms + spindle in one piece). http://sheldonbrown.com/opc.html

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    ^^ Lay off with the "Read again" bit, will you?
    It has not been proven that the OP has an Ashtabula crank, only that it is not a cottered crank.

    Whatever it is, and without photos I don't think any of us can tell whether it's an Ashtabula or a one-piece forged crank & spider (as opposed to swaged), the OP has managed to fix her bike by figuring out which things are loose and tightening them, and that's the main thing. "Well done" to her.

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