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Thread: bent chainring

  1. #1
    Senior Member peripatetic's Avatar
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    bent chainring

    So a friend showed me his bike, a very old (70s, maybe older) Huffy and he asked me why his chain was skipping. He's been riding it singlespeed with no front derailler and no shifters. I looked and noticed that the chain was gunked to heck: he used motor oil to lube it. Anyway, it also turns out that the chainring got banged by a car, and it's slightly bent. I looked down at the bb, and noticed that the driveside bb cup was a little loose. The cranks are steel, one-piece, with a three-arm chainring. My questions follow:

    1. Should I tell this guy to get a new bb and chainring, or can he just get the bearings re-packed and the cup tightened up?

    2. Will continuing to ride it with the bent chainring lead to further problems?

    3. Can one find three-arm replacement chainrings easily, as well as bbs that'll fit?

    4. Ultimately, I'm trying to figure out what the most efficient and cost-effective solution to this maintenance problem would be, so if you just want to throw that at me, I'd appreciate that. (No, buying a whole new bike is not an option, and though I'm no fan of Huffys, this one actually seems decent, and has definitely shown its worth over a long time.)

  2. #2
    JRA...
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    i would checksheldon brown's page on straightening chainrings. if it can't be straightened, replacing the chainring is not terribly hard on 1-piece cranks, sheldon has an article on this as well. as far as the loose cup goes, as crude as it sounds, you can remove the cup during overhaul, and lightly peen the edge of the BB shell to decrease its diameter. it's not uncommon to find that cups on those bikes are ovalized; a complete cup and cone kit should be around $10.

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    Senior Member peripatetic's Avatar
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    Okay, but what of three-armed spiders/chainrings? Can those be found easily in LBS parts bins and such, or does one have to go scrounging ebay? Sheldon's page speaks of a conversion kit for three-piece cotterless cranks. Anyone know where these can be found?

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    if it's the normal, old-fashioned one-piece crank with a pin in the crankarm to keep the chainring from rotating freely, a chainring from any other of the same type will fit. may have trouble finding a new double, but there's a million of those cranks/chainrings around. or you could just put a single in; only problem with that is that you make have trouble finding anything larger than 44T. if you're willing to lay down for one of those conversion kits, you might as well buy a new dept. store bike. the kits alone start around $20, not including bb or cranks.

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    also, rereading you original post, check his drivetrain. if he's been oiling his chain heavily and has been riding around in shifterless, default mode (ie, small/small), good chance his drivetrain is shot. mo headaches, mo money.

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    Senior Member peripatetic's Avatar
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    Hmm. That's what I thought. Okay, I guess I'll go scrounging around for a used chainring if we can't get this one bent back alright. Thanks for the info.

    In terms of servicing the bb, I really just need to get new bearings and retainers, and can probably get by with the original cups, huh?

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    to be honest, if nothing looks worn irregularly, just clean it well and put it back together (grease of course). i suspect this is going to be a bigger project than you're anticipating and the money may be needed elsewhere. but to answer your original question, probably yes, but you're not saving much; parts-greater-than-the-whole deal.

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    Bend the chainring back with a pair of pliers or a crescent wrench. You really don't have to get a chainring that true, if just being used on a beater bike or the like.

    Don't put new retainers in there, just put straight ball bearings/grease.

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    Quote Originally Posted by BostonFixed

    Don't put new retainers in there, just put straight ball bearings/grease.
    in a ashtabula BB? what a PIA, and not really worth the extra effort on the machine.

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    Quote Originally Posted by BostonFixed
    Bend the chainring back with a pair of pliers or a crescent wrench. You really don't have to get a chainring that true, if just being used on a beater bike or the like.

    Don't put new retainers in there, just put straight ball bearings/grease.

    Well, aside from the fact that the chain's going to wear the teeth on the ring unevenly, isn't it possible that the bend in the ring is causing the chain to skip? I figure that it's either that, or it's the fact that the chain's gunked and crudded like crazy from being ridden for two years with motor oil on it . I saw that thing today and had to suppress a serious guffaw. Dude admitted that he knew nothing about maintaining bikes. I told him that using motor oil was better than using nothing; there definitely wasn't any rust on the chain, nor on the rest of the bike for that matter. But I digress...

    I guess I just always find it amazing the things that people will do to their bicycles in blissful ignorance.

  11. #11
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    a bent chainring generally will cause the chain to roll off, or cause a "popping" sensation/noise. skipping is usually cause by a shot drivetrain, stiff links, or a maladjusted/shiften derailleur.

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