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Crank Arm Bolts FALLING OUT--HELP!

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Crank Arm Bolts FALLING OUT--HELP!

Old 04-15-09, 06:53 PM
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Crank Arm Bolts FALLING OUT--HELP!

Hello,

Today I was on a ride when I noticed my left crank arm/pedal was feeling wobbly. I quickly pulled over to see that my crank arm bolt had been loosened (it hadn't fallen out, but was loose enough that I was re-tightening it with my hand) This is on a Shimano UN54 square taper bottom bracket and a Pake fixed gear/SS crank. I tried researching this but didn't get any good answers...do I just need to re-install that left crank arm? A bike mechanic at my LBS had installed it originally but I have reason to believe he did a shoddy job. He was installing a chain and new Pake crank onto my fixed gear bike and when I was walking out the door, the left crank arm fell off. I said "hey, I think you forgot to install this left one..." He took it back and presumably installed it really quickly. Now, 2-3 weeks later, it's falling off...

Are my cranks/BB ruined???? I really hope not...Do I just need to re-install this crank arm (probably at a different shop)??

Thanks for your help

Ben
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Old 04-15-09, 06:58 PM
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it might be ok, it might not be ok. if you pull your crank arm off and there are new notches in there (stripped, rounded), then you'll have to replace the crank arm because it'll keep coming loose.

if not, then most likely it's safe to just tighten it and ride it.
more than likely only the cranks need to be replaced because the BB spindle is made from steel, which is harder than aluminum.
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Old 04-15-09, 06:59 PM
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You could just reinstall it and try it. If it comes loose again it is basically junk. If it was a new crank the shop should replace it. if used it could have been damaged previously. Either way I would find a new bike shop. Roger
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Old 04-15-09, 07:03 PM
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I got it online from Bell's bike shop and it was new. It was installed at a LBS that isn't the best but is really close to my house. I might just go buy a ratchet type wrench and tighten it back on myself. Will I need to use loctite for that? Also, how should I put the crank arm on before I tighten the bolt? Should I hammer at it with a rubber mallet? Should I just press it on firmly with my hand?
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Old 04-15-09, 07:57 PM
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just grease the threads, the bolt will automatically tighten the crankarm properly with the correct amount of tightening.
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Old 04-15-09, 08:48 PM
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I am afraid it is very likely your crankarm needs replacing. The most likely cause of the problem, I would guess is that the bolt was either left too loose, or the bolt was overtightened. A defective taper in the crank could also be the culprit, but this is rare.

If there is any damage to the taper the crank will continuously rock slightly, which makes the damage worse, which increases the rocking. It also ratchets off the bolt a tiny bit with every turn of the pedals. And as said above, since the crank is made of a much softer material it cannot withstand much use if it is not secured properly to the spindle.

In conclusion, the crank did not fall off because your bolt was loose, your bolt was loose because your crank was falling off. Or is that the other way around?

Anyoo, check the faces of the crankarm taper carefully. I'll bet my last donut that the taper is either flared out from being pushed too far onto the spindle, or has dents from rocking on the spindle.

If there is any damage do not try to reattach the arm and ride the bike, as riding with a damaged crank taper can round the edges of the spindle, which might damage subsequent crankarms. If you stopped riding reasonably soon after your crankarm fell off then the spindle is likely free from damage.
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Old 04-15-09, 09:05 PM
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Probably you will need a new crankarm.

When you get your new crank arm, watch your bike shop lightly grease the spindle and use an actual torque wrench to install. If they don't, pick a different bike shop.
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Old 04-15-09, 09:55 PM
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so I just checked the taper on the crank arm and it looks perfect. I took my super bright bike light and shined (shone?) it inside the taper, and all 4 sides look completely straight and there doesnt appear to be any sort of damage. Also, the bb spindle looks fine, too. I checked this very thoroughly and it does look perfect as far as I can tell.

I am definitely taking it to a new shop tomorrow to have them re-install it. I did stop riding as soon as I felt the pedal feeling wobbly.
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Old 04-16-09, 07:46 AM
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With the crank arm off check your bolt and its' threads. Are the threads stripped from the bolt or the spindle?
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Old 04-16-09, 07:52 AM
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I seem not to be able to tell visually if the taper of a crank is ruined. For me, the only way to tell is if it keeps coming loose. So, either go back and complain to the LBS, or else tighten it on there again and see.

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Old 04-16-09, 09:42 AM
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I retract my previous statement. The crank arm is most definitely ruined. It looked absolutely fine, but apparently it wasn't because when I put it back on the spindle, I just pressed it on there firmly with my hand, and it was rocking back and forth a good inch. Ugh. Now I'm just hoping I didn't ruin my bb spindle as well. I put on this old crappy crank to see if it would work, and the left one was rocking back and forth, but just a tiny bit, like a mm worth. Is that still bad? Does that mean the BB is ruined, too?
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Old 04-16-09, 10:00 AM
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If there is "play" it will only grow larger. Have you tried the LBS that fubar'd your cranks?
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Old 04-16-09, 11:40 AM
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Your spindle could be fine. And, lest we alarm you too much, there's not much catastrophic that's going to happen here. I'd actually try putting the crank on all the way to make sure it's actually dead. Worse case scenario: it loosens up again. If you have in fact toasted your spindle, which I think unlikely (steel vs. aluminum: steel wins), a new BB is $25. Not the end of the world.
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Old 04-16-09, 11:51 AM
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According to Shimano, the correct torque for their crank-arm bolts is 305-391 inch-pounds. If that doesn't hold and/or gets loose - toss it.
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Old 04-16-09, 11:56 AM
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1. Make sure you have a hardened steel washer between the crank bolt and the crank.
2. Tighten the bolt down HARD - use at least a 12" wrench handle and lean into it.

Or, take it back to the LBS and tell them to try again.
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Old 04-16-09, 12:53 PM
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Originally Posted by PedallingATX
I retract my previous statement. The crank arm is most definitely ruined. It looked absolutely fine, but apparently it wasn't because when I put it back on the spindle, I just pressed it on there firmly with my hand, and it was rocking back and forth a good inch. Ugh. Now I'm just hoping I didn't ruin my bb spindle as well. I put on this old crappy crank to see if it would work, and the left one was rocking back and forth, but just a tiny bit, like a mm worth. Is that still bad? Does that mean the BB is ruined, too?
It is going to feel loose unless you put it on properly. I'd take it by the same LBS & have them put it on again for free. If it comes loose again then they owe you a new crank arm for not putting it on correctly in the first place.
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Old 04-16-09, 01:07 PM
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Okay, so this is the most confusing problem I have ever encountered working with a SS/FG bike. It only felt wobbly when I was pressing it on the spindle without tightening the bolts. So, as you guys suggested, I took it back to the LBS that botched it the first time, and he re-installed that crank arm, using a torque wrench and putting a lot of elbow grease into it! It doesn't wobble now that it's tightened on, and I rode it to school today and am just going to wait this thing out and see if it gets worse. Hopefully, now that the bolt has been properly torqued, it will be fine. I will definitely update you guys on what happens here in the next few days (I ride A LOT). Thank you so much for all your help!
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Old 04-16-09, 01:13 PM
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Mine did that too (Campy cranks). I put it on the last time with a torque wrench and also put a little loctite on the threads. Hopefully it'll stay put this time.
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