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  1. #1
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    Sheared Crank Bolt Nut Removal.....help please

    I'm no DIY or bike expert, so please advise in easy language!!

    I was riding my Giant Warp DS2 last night, and the right crank arm decided to just come off, leaving me stranded 15 miles out in the stix.....finally got home and saw that the Crank bolt nut has sheared off. Please see this photo.

    http://www.spenmusic.com/Site1/Blank.html

    If I'm right in my thinking (please tell me if I'm wrong), I need to get the remains of this nut out, and replace it with a new crank bolt.

    Any ideas on how to get this out? It looks solid. I don't know whether to try drilling it, or if there is another method. If I need to drill it, what drill bit? Stupid question, but I'm useless at DIY etc.

    Thanks in advance.

  2. #2
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    It's hard to tell from the picture but if there is any part of the bolt sticking out beyond the spindle end, try clamping a pair of Vise-Grips on it and unthreading it. Otherwise you are going to need to center drill the bolt and use an EZ-Out to remove the stub. If none of that makes sense, you need to get to a bike shop for the repair.

    BTW, I presume the crank arm that came off is ruined since riding with it loose will have damaged the square mounting hole beyond use.

  3. #3
    Old Fogy
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    Terminology: A bolt is a threaded rod, a nut is the part that screws on the bolt. From the picture, that looks like a bolt.
    Usual method is to use a tool called a screw extractor, one popular brand is Easy-out, looks like a tapered rod with spiral flutes, or maybe a square tapered bar made of tool steel, with sharp corners. Get one half or two thirds the diameter of the bolt, and then drill a hole to fit it. Tap the extractor into the hole and turn it to unscrew the broken bolt. Likely won't be tight enough but what it will come out quite easily.
    There are other ways, but require a bit more skill than you profess to have. (Yet. You'll learn.)

  4. #4
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    Best Scenario: An EZ Out. Remove the broken bolt, install a new crank arm and bolt it back up and away you go.

    The SOL Scenario: You need a BB!

  5. #5
    Senior Member Iowegian's Avatar
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    The easist solution would be to replace the BB. You might need a new crank arm as well if the square hole is mangled.

    Removing that bolt remant is not an easy job for anyone and with your lack of tools and experience I wouldn't even try it. You can get a Shimano UN-54 that will be a direct replacement for your current BB for something like $20.

    You'll need to know how long the spindle of your current BB is so you can get an exact replacement. To find this, you'll need to take the other crankarm off and measure the length from end to end. It should be something like 107mm, etc. Also measure the length of the BB shell on the frame. It should be 68mm or 73mm. Then find a BB that matches these 2 numbers (ebay will have one) and take the BB and the bike to your LBS. If you don't know how to do any of this stuff check out the Park tools website. They have how-to's on all this stuff. Or find a friendly LBS or bike coop or a friend who works on bikes to help out. You will need some special tools to replace the BB but I still think it will be the easiest solution in the long run.

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    Thanks for all the info guys.

    I'm going to buy a new BB. I have checked on the Giant website and mine should be 113-68mm.

    There seem to be lots of different model numbers (TH 7420ST, UN26 etc.), but I guess they are all pretty much the same.

    I'm in Japan, & want one ASAP, so I'm going to buy this off auction

    http://page18.auctions.yahoo.co.jp/jp/auction/w43585316

    Please let me know if you think it is OK, given the info. that I have from the Giant website.

    The crank arm is OK, no need for a new one.

    So just one last issue I have now....to replace the BB myself, what tools will I need?

    I have taken the remaining 8mm crank bolt out of the left hand side, but from here, I can't remove the crank arm. What do I need to do this, and then, any other tools to remove the BB?

    Thanks

  7. #7
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    Quote Originally Posted by speni View Post
    The crank arm is OK, no need for a new one.
    Are you sure of that? The crank arm may be intact but the square hole for the bottom bracket spindle is likely to have been damaged and it will never fit correctly or stay tight again.

    As to bb replacement, you seem to me to be in way over your head with this project. The first thing you need to do is carefully read the Park Tool web site's description of the job and the tools needed.

  8. #8
    Primate Metzinger's Avatar
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    You'll need a splined bottom bracket tool for Shimano BB replacement. Here's how to use it.

    First you'll need to get that other crank off with a crank puller.

  9. #9
    Primate Metzinger's Avatar
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    But first, let that friendly mechanic at the local garage have a look at that bolt.
    Auto mechanics are constantly dealing with trouble bolts.
    Just because the end broke off, doesn't mean the bolt will be tough to extract.
    Could be the 10 minute solution. Then you'd just need a new bolt.

  10. #10
    Senior Member Iowegian's Avatar
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    NOPE! That BB won't work for you. That is an Octalink BB and you need a square taper one. Look at the end of the spindle to see the difference. A UN-26 should work fine but whatever you get, you need a square taper 113-68.

    You need a crank puller to remove the crank arm.

    Start here: http://www.parktool.com/repair/readhowto.asp?id=103

  11. #11
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    OK, I understand all that thanks. I've got all the tools ordered, and I think this is the right BB..

    http://www.amazon.com/Shimano-BB-UN2.../dp/B000F5HXHS

    In Japan, it's hard to get the local mechanic/LBS to just have a quick look, the bike has to be booked in, left, ......gets pricey before you've had time to scratch your backside. Everything by the book, then top price for any parts, so I'll have a go myself.

    Thanks for all the help, I'll let you know how I get on when the stuff arrives.

  12. #12
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    have you tried to turn it by picking at it with your fingernail?

    have got 3 broken crank bolts out like that.

    maybe try a screwdriver or a knife to turn it if you cant get your finger nail on it

  13. #13
    Elitist Troglodyte DMF's Avatar
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    Quote Originally Posted by HillRider View Post
    Are you sure of that? The crank arm may be intact but the square hole for the bottom bracket spindle is likely to have been damaged and it will never fit correctly or stay tight again.
    It was ruined even before the bolt sheared. Bolts don't just shear for no reason. When properly installed there is no (or very little) shear stress on the bolt. But if the bolt loosens and the crank arm backs off the spindle a little, it will put a lot of shear stress on the bolt -> <snap>.

    speni, replace the crank arm or you'll just have this happen all over again.
    Stupidity got us into this mess - why can't it get us out?

    - Will Rogers

  14. #14
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    Job done. I drilled a screwdriver "slot" into the bolt, and managed to unscrew it.

    I spoke to the guy who had the bike before me, and he said he regularly had to tighten this nut, and maybe had done it too harshly, and it has sheared, hence the crank arm is still OK.

    I don't know why this bolt regularly needs tightening up, maybe in the future I will need a new BB.

    Thanks for all your advice, got there in the end.

  15. #15
    Primate Metzinger's Avatar
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    Quote Originally Posted by speni View Post
    I spoke to the guy who had the bike before me, and he said he regularly had to tighten this nut, and maybe had done it too harshly, and it has sheared, hence the crank arm is still OK.

    I don't know why this bolt regularly needs tightening up, maybe in the future I will need a new BB.
    Well done on getting that bolt out. You're not in the clear yet.

    With every pedal revolution, the crank wobbles a bit and pushes against the bolt that's trying to hold it on.
    The bolt needs constant retightening because the hole in the crankarm is deformed. It's also why it broke.
    This is a classic problem.

    I know that it's not the spindle because the crankarm is made of softer metal.

    This problem will continue until you get a new crankarm or new crankset.

  16. #16
    Svr
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    Quote Originally Posted by speni View Post
    I spoke to the guy who had the bike before me, and he said he regularly had to tighten this BOLT
    That usually means the square taper in the crank arm has become oversized.

  17. #17
    Elitist Troglodyte DMF's Avatar
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    Quote Originally Posted by DMF View Post
    It was ruined even before the bolt sheared. <snip>

    speni, replace the crank arm or you'll just have this happen all over again.
    Read this again.
    Stupidity got us into this mess - why can't it get us out?

    - Will Rogers

  18. #18
    I suck, but you're worse
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    Actually a bad crank arm is what caused the shearing in the first place. Get a new crank arm.

  19. #19
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by speni View Post
    Job done. I drilled a screwdriver "slot" into the bolt, and managed to unscrew it.

    I spoke to the guy who had the bike before me, and he said he regularly had to tighten this nut, and maybe had done it too harshly, and it has sheared, hence the crank arm is still OK.

    I don't know why this bolt regularly needs tightening up, maybe in the future I will need a new BB
    .
    The bolt regularly backs out because the crankarm's hole is completely buggered. It squirms on the spindle and wiggles the bolt loose. Screwing on the bolt tighter doesn't do anything to solve the problem (except to break the bolt). Take a closer look the inside of the square-taper hole on the crank and you'll see that it's NOT a perfectly square taper. most likely it's flower-shaped with rounded corners. THAT is why it's wiggling on the bottom-bracket spindle and loosens the bolt.

    The bottom-bracket is fine in this case. Hardened steel cannot be damaged by soft aluminium. You just need a new crank and bolt. Install to proper torque the FIRST time. You have only one chance to install the crarnkarm correctly. If it loosens just once, you've pretty much destroyed it. No amount of re-tightening that bolt will ever keep it on. Just do a search here for "loose crankarm" and research more deeply into this issue.

  20. #20
    cab horn
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    Quote Originally Posted by sooprvylyn View Post
    Actually a bad crank arm is what caused the shearing in the first place. Get a new crank arm.
    No.

    It's the fact that the previous owner tightened it repeatedly after the crank become loose that is the problem.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  21. #21
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    If the crank is torqued properly it does not need to be retightened. The previous owner did not install it right.
    http://draco.acs.uci.edu/rbfaq/FAQ/8f.11.html

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