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My crank arm fell off while riding

Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

My crank arm fell off while riding

Old 07-02-08, 06:49 PM
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Ezek
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My crank arm fell off while riding

Has anyone ever had this happen before? I've only been riding for 3 years and I have never experienced this before. My bike is only a year old, is it how my lbs put it together? Someone tell me yes, I want a good reason to go back and complain, their service is horrible.
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Old 07-02-08, 06:55 PM
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To your questions:

1. No, not personally.
2. Yes, probably your fault. Or a mfg defect on some part, but more likely your fault through poor maintenance. Which is shocking, I think.

I am glad you were not injured when this happened.

Last edited by prendrefeu; 07-02-08 at 07:10 PM.
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Old 07-02-08, 07:02 PM
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have you ever tensioned your crank? After 300 miles when you purchased your bike you should have locked it down. If not, your crank came loose and you have probably stripped the square taper of the bb and the crank. You may need to replace the whole lot. Examine it carefully.

I know, I did the same thing.
If you stripped it replace the bb and crank.
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Old 07-02-08, 07:06 PM
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After a year I would say the blame is solidly in your corner. It was probably creaking for some time before it fell off. If it's an Octalink/ISIS bottom bracket, it's probably fine.
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Old 07-02-08, 07:17 PM
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Originally Posted by slim_77 View Post
have you ever tensioned your crank? After 300 miles when you purchased your bike you should have locked it down. If not, your crank came loose and you have probably stripped the square taper of the bb and the crank. You may need to replace the whole lot. Examine it carefully.

I know, I did the same thing.
If you stripped it replace the bb and crank.
O dam, now I gotta worry about my crank falling off. Geez. Anything else for an old guy to worry about?
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Old 07-02-08, 07:19 PM
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Seriously, I have over a 1000 miles on my bike and have never done anything to the crank. what should I do?
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Old 07-02-08, 07:20 PM
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Tighten the bolt that attaches it to the BB.
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Old 07-02-08, 07:22 PM
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Lock it down and carry a tool with you on every ride! Mine fell off (last year) on my way to work...

If it comes loose again, well, hey...
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Old 07-02-08, 07:25 PM
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Originally Posted by slim_77 View Post
Lock it down and carry a tool with you on every ride! Mine fell off (last year) on my way to work...

If it comes loose again, well, hey...
Yours fell off last year, why live?
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Old 07-02-08, 07:25 PM
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Ok I will go check it right now.
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Old 07-02-08, 07:29 PM
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it happened to me. What kind of crank/bb do you have?

Mine is a shimano/outboard kind. I built the bike.....so my fault. The dustcap came off at some point, and it slowly worked it's way off. If I didn't hang my bike "BF style" w/ the crankset facing me I might have caught it. I also might have caught it if I ever inspected my bike pre-ride.
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Old 07-02-08, 07:46 PM
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What kind of cranks do you have? At some point you're going to have to wrench on your bike. You have to maintain your motor -- why not your bike?

Depending on the crank you may have to get some Loctite.
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Old 07-02-08, 07:58 PM
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kudude - that dust cap is not a dust cap, it's used to tension the cranks on the bearings while the pinch bolts are loose. Then you tighten the pinch bolts which locks the tension bolt in place.
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Old 07-02-08, 08:11 PM
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Originally Posted by 62vette View Post
kudude - that dust cap is not a dust cap, it's used to tension the cranks on the bearings while the pinch bolts are loose. Then you tighten the pinch bolts which locks the tension bolt in place.
things I know now.

Somehow while learning to work on cars I never lit anything on fire. I learn many things the hard way.


Anyway -- bearing preload is important, just like in the headset. You are correct. Putting together the bike the first time, well, anyway. Now I know.


edit: now that I think about it, that second line isn't really true. It just happened to be on purpose.
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Old 07-02-08, 08:16 PM
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I have installed probably a half-dozen cranksets on various bikes that I've built up over the years. I always install the bottom bracket and the crank-arm fixing bolts with a torque wrench. Not one has ever come loose. In my experience, if they are installed correctly, they will stay tight. If they are installed incorrectly, then yes, they will come off.

I'm not the strongest guy, but there's no way I could get anything close to proper torque on a crank-arm fixing bolt with standard T-handle allen wrenches or one of those little multi-tool things. Basically, if you install the bolts to "yeah, that's tight" -- then yes, I can believe the crank-arm will fall off at some point.

Basically, if I got a new bike, and the crank arm fell off, I'd be seriously PO'd at whoever did the installation. Most likely either the crank arm itself or the BB spindle is damaged.

Should the OP have gone in for some 300-mile checkup? Sure. I'm not convinced that would have fixed anything -- i.e., if the LBS did a "yep, that feels tight" installation in the first place, they're probably going to do a "yep, that still feels tight" basic check during the 300-mile checkup as well.

I think the lion's share of the blame goes to whoever did the installation in the first place.
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Old 07-02-08, 09:06 PM
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Originally Posted by KevinF View Post

Basically, if I got a new bike, and the crank arm fell off, I'd be seriously PO'd at whoever did the installation. Most likely either the crank arm itself or the BB spindle is damaged.

Should the OP have gone in for some 300-mile checkup? Sure. I'm not convinced that would have fixed anything -- i.e., if the LBS did a "yep, that feels tight" installation in the first place, they're probably going to do a "yep, that still feels tight" basic check during the 300-mile checkup as well.

I think the lion's share of the blame goes to whoever did the installation in the first place.
I agree that the mechanic is largely to blame. I also agree that they probably wouldn't have checked it during a tuneup. They generally just check cable tension at that time.

I don't like anyone else to work on my bikes, so having bought a new road bike this year, I actually loosened and retightened everything to specified torque so it is all my responsibility. Unfortunately, you can't just check torque by tightening and seeing if your wrench clicks because of momentum.

Unfortunately, those who don't do their own maintenance are at the mercy of their mechanics for things like this.

OP, I would gripe to the shop where you bought the bike.
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Old 07-02-08, 09:56 PM
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Yes, it happened to me last winter. Less than 50 miles on my new bike, cranking up hill and the left crank arm came off still attached to my shoe. I slowed down then fell over. The mechanic at my LBS had not tightened the pinch bolt. The crank arm was damaged and replaced by the LBS along with many apologies!
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Old 07-03-08, 03:26 AM
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Ive had it happen, lack of tightening on my part.

Sometimes you can save them by really torqueing them down of they ddint come completely off.
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Old 07-03-08, 04:16 AM
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At least is wan't a WHEEL !!
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Old 07-03-08, 05:14 AM
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Looked at the thread title, and thought: "Another Who-Can-I-Blame thread".

As far as I am aware, bikes are box-delivered with the cranks installed by the factory. It might be a warranty job, so be nice to the bike shop before blaming THEM.

Otherwise, check your bike over before you ride it.
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Old 07-03-08, 07:27 AM
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Originally Posted by KevinF View Post
I have installed probably a half-dozen cranksets on various bikes that I've built up over the years. I always install the bottom bracket and the crank-arm fixing bolts with a torque wrench. Not one has ever come loose. In my experience, if they are installed correctly, they will stay tight. If they are installed incorrectly, then yes, they will come off.

I'm not the strongest guy, but there's no way I could get anything close to proper torque on a crank-arm fixing bolt with standard T-handle allen wrenches or one of those little multi-tool things. Basically, if you install the bolts to "yeah, that's tight" -- then yes, I can believe the crank-arm will fall off at some point.

Basically, if I got a new bike, and the crank arm fell off, I'd be seriously PO'd at whoever did the installation. Most likely either the crank arm itself or the BB spindle is damaged.

Should the OP have gone in for some 300-mile checkup? Sure. I'm not convinced that would have fixed anything -- i.e., if the LBS did a "yep, that feels tight" installation in the first place, they're probably going to do a "yep, that still feels tight" basic check during the 300-mile checkup as well.

I think the lion's share of the blame goes to whoever did the installation in the first place.
I've seen Dura Ace, new Record, SRAM Rival, and Truvativ Roleur Carbon cranks all come loose after being tightened to the proper torque specs. The latter two were my personal bikes.

The OP didn't maintain his bike. Simple as that. To expect everything to be tight and properly fitting after a YEAR is ridiculous.
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Old 07-03-08, 07:52 AM
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Ezek, was this a square taper crank, octalink/isis, or something with external bearings?

Back when dinosaurs wandered the earth and people with actual engineering backgrounds discussed bikes on the internet, there was a lot of discussion about square taper cranks and how the crank tends to squirm up the spindle, leaving no pressure on the bolt, which can then back out, and then the crank can fall off. The moral of the story is that for a square taper crank, unless the bolt can be loosened by hand you don't want to keep tightening it repeatedly as you end up chasing the crank up the spindle until the steel spindle ultimately prevails over the aluminum crank.
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Old 07-03-08, 09:07 AM
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I had a square taper Campy come loose on me a few months ago. Fortunately, I noticed it was loose and got off the bike right away. My wife rode home and got the car. I got lucky and didn't damage the crank arm but usually that means death for the crank arm.

That was the 1st time in nearly 30 years of doing my own crank maintenance that I didn't get it right. It seems to me that the Campy square taper (Centaur anyways) requires alot more torque to properly seat on the spindle than in years past. (Or maybe I'm just getting old )

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Old 07-03-08, 09:13 AM
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I dont know if I ever want to do my own crank maintanence.
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Old 07-03-08, 09:17 AM
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Originally Posted by Ezek View Post
Has anyone ever had this happen before? . . .
Yep. Lost the bolt; far from home; major PITA. It telegraphed little warning between the "loose" and "off" status; in fact the crank arm and pedal were still attached to my foot when it detached; alternately pedaled one-legged and walked back.

Nekura mentioned LokTite. Any drawbacks to using a dab?
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