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  1. #1
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    Help w/ broken crank arm

    I'm still a beginner got out about 15 times last year and had a crank arm (not sure if thats the name) but that fell off during a ride. I was able to get it back on to get back and then had a local bike shop finish the repair. Whatever they did wasn't good enough cause I was tightening the bolt 3-4 times while out on it and the last time I was out it fell off again. Anyways the main bolt that secures the arm is a little bent and beat up and I'm trying to figure out my best course of action for repair while not spending a fortune.

    Do I just buy new arms and bolts? new crankset? I really know nothing about cranks.

    The crankset that is on the bike is TruVativ 5D Aluminum Triple 22/32/42T 175mm

    my bike is a 23inch Motobecane 600HT
    also I;m 210 so I need something that will hold my fat ass. thanks in advance

  2. #2
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    I had a problem similar to this.

    I'm guessing your crankset design is square taper. You can tell by looking at the crankarm and seeing if it has a square that essentially slides onto the bottom bracket.

    Chances are you rounded out the square if you were riding it while it was loose. You should be able to replace the arm for around 15 dollars at your lbs. Make sure you tighten it back on to torque specs, or else it will get trashed again very quickly. When you tighten it to spec it actually slides the square up the bottom bracket, which is slightly tapered (hence the name square taper). If it's tightened properly you should be able to remove the bolt and ride it without any immediate problems (while not recommended).

    Hope that helps.

  3. #3
    Rod
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    If it's the left crank arm you should follow vitale's advice and just replace the crank arm if that's necessary or just the bent bolt. I would have to see it. It's not big deal, but I would put lock tite (sp) on the bolt so it won't back off again. My friend had his left crank arm fall off a few times while he was riding and I think that finally solved the problem.

    If it's the right crank arm, which I'm doubting that's another story. According to the owner of my lbs the right crank arm costs almost as much as a new crank. If that's the case it's time to upgrade your crank.
    There is not much choice between rotten apples.

  4. #4
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    The right side crank arm almost never falls off unless you break the bolt.
    It's always the left. Anyways, what I did was clean out the threads of the taper with some degreaser or brake cleaner of something similar. Watch your eyes!!!!!!!
    Then clean off the bolt with same cleaner. Make sure everything is really dry and put some blue loctite on the bolt threads and let it sit for like 5 minutes....or until it seems kinda dry. Put the crank arm back on, then torque the bolt back on. TIGHT.
    If it falls off again, use RED Loctite, and follow the same process. If it falls off after that its time to get a new crank arm, or even better yet, find some new cranks with the spline type BB. Or better yet, the newer type cranks with outboard bottom bracket.

    I'm a bit heavier than you, and had this same problem. The blue loctite worked for about 3 months. The red worked until I decided to change my cranks....but DO NOT use the red unless the blue doesn't work. Being bigger guys, we are really better off with the newer style outboard BB cranks. I love mine, and would never go back.
    Try the Loctite first, and it will prolly work if you follow the directions.....and buy you some time to save up for some newer cranks.
    You can get Loctite at any hardware store. But start with the blue. Its only a few bucks.

  5. #5
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    I have experienced this kind of problem and solved it the simplest way possible - just by screwing the bolt in stronger - after attempts to fix it at the shop failed. Truvativ recommends greasing the bolt's thread, it's why I am not sure about using locktite.
    I attached the screenshot of the manual for square taper. As far, as the bolt's thread is concerned, same stands for splined bottom bracket interface .
    Most Allen keys are just not long enough to tighten the bolt up as needed. I have used a ring key(around 15 mm), putting it on the Allen key and using its handle to get more leverage. It takes being careful, though, to not ruin the thread.
    It is hard to believe, that after just 15-20 rides anything in the crank might wear out.
    Attached Images Attached Images

  6. #6
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    Thanks for the replies. I'm going to get a new left arm and bolt this weekend and add some blue locktite to secure. Any idea of how much the bolt and arm should cost me? I'm guessing these are common parts and I can pick them up at any lbs?

  7. #7
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    I would guess the parts would cost around $25. I wouldn't guarantee they'll have the parts available, but they should be able to order.

    If you don't want to deal with the LBS, Here is the crank arm you'll need, but I don't think it comes with a bolt.

    Truvativ Crank
    http://www.jensonusa.com/store/produ...=BBBSEARCH&x=y

  8. #8
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    thanks it is square taper. the Truvatic one is exactly what I have/need.

    sorry for being a noob but is the bolt standard?

  9. #9
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    Quote Originally Posted by bowman81
    thanks it is square taper. the Truvatic one is exactly what I have/need.

    sorry for being a noob but is the bolt standard?

    Yeah the bolt is very standard. I'm sure any shop would have a bunch of those lying around.

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