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Left crank arm fell off a week after maintenence tuneup

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Left crank arm fell off a week after maintenence tuneup

Old 08-04-14, 01:56 PM
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Left crank arm fell off a week after maintenence tuneup

Hi guys,

I had a Giant OCR 3 that had been sitting around for a couple of years without any riding action. I recently took it in to a bike shop to have it inspected and tuned up for riding. As they were working on it they called me on the telephone and told me I needed a new bottom bracket. I said sure, put it on. About the 5th ride since I got the bike back, the left crank arm fell off in the middle of the ride.

Never mind that I wasn't injured, but I don't know too much about bike maintenance. Honestly, that's why I took it to them. To fork over the $150 for parts and labor to get a bike back that worked. So I'm a bit discouraged. I'm posting here to see what you guys would do, and maybe gather some knowledge about bike mechanics so that once I go back to a bike tech I can not look so foolish. I'm wondering if they just did a totally shoddy job or if maybe my crank arms were too old?

Thanks.

Last edited by kierkegaards; 08-04-14 at 01:59 PM.
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Old 08-04-14, 02:04 PM
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I don't know what type of cranks your bike has, but generally when a crank falls off, it's a square-taper crank, and whoever fitted it didn't tighten the fixing bolt (or nut) hard enough. If that's the case, it's the fitter's fault.
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Old 08-04-14, 02:13 PM
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.. back to the LBS
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Old 08-04-14, 02:15 PM
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Originally Posted by fietsbob View Post
.. back to the LBS
Nope.

Back to a DIFFERENT LBS.
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Old 08-04-14, 02:20 PM
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or buy tools to keep your stuff .. up to snuff


if the arm is damaged shop B wont fix shop A's mistakes for free (with mia culpas), then you pay out of pocket.
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Old 08-04-14, 02:50 PM
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Just go back and tell them what happened. If they are apologetic, give them another chance. If not, I'll look for another shop.
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Old 08-04-14, 02:50 PM
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Originally Posted by achoo View Post
Nope.

Back to a DIFFERENT LBS.
partly Yes, ansd NO.

Step 1 go back to the original LBS and have them deal with it immediately, while they send you around the corner for a slice of Pizza by way of apology.

Step 2 find a better shop. $150 should buy a decent amount of work, and if it included replacing the BB they have no excuse on the crank front.

If when you bring it back, the manager apologizes profusely, and seems angry and aggravated (at his employee, not you) and offers (on his own initiative) to recheck the entire job, then I might consider giving them another chance.
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Old 08-04-14, 03:47 PM
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Here's what probably happened:

Lots of bike mechanics - maybe even the majority - will tell you they don't need a torque wrench. In some cases, that's probably true. The torque spec for a square taper crank arm is around 30 ft/lbs. That's a pretty good amount - more than I would probably use if left to my own devices.

If square taper crank arms aren't sufficiently torqued, they start to wiggle. As they wiggle, they reshape the square hole in the crank arm. If you let it go too long, not only will the crank arm come off, but it might no longer stay in place regardless of the amount of torque used. Having come off once, your crank arm might not be past this point of no return, but I wouldn't count on it.

Incidentally, it's possible to over torque square taper crank arms too. When that happens they crack out at one of the corners of the square hole.
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Old 08-04-14, 04:42 PM
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Originally Posted by Retro Grouch View Post
Here's what probably happened:

Lots of bike mechanics - maybe even the majority - will tell you they don't need a torque wrench. In some cases, that's probably true. .....
The use of torque wrenchws on bicycles is a relatively new phenomenon. Not counting a fringe element that confuses bicycles with space vehicles, nobody started using torque wrenches until the advent of carbon parts. That's after the square taper crank was already being phased out on better bikes. In the heyday of Sq. taper, millions upon millions of these were installed and maintained by both pros and amateurs with no serious issues. (Yes, some did work loose, but the numbers are small and consistent with other mechanical issues).

So, maybe younger mechanics that were never properly trained might not know how to properly torque a crank bolt, but the vast majority of mechanics, pro and not, can and do install these reliably time after time.

It's not a question of tools, it's a question of skill, and more important, craftsmanship and care.

BTW- if we continue to foster the ridiculous notion that torque specs have to be looked up for every mundane job, the cost of bicycle repair will increase beyond the reach of most of the public, and we'll be moving to throwaway bicycles.
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Old 08-04-14, 04:50 PM
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It seems possible to me that the arm's square hole was damaged to a non-square shape before @kierkegaards brought the bike into the LBS. The LBS didn't notice this or notify him. Maybe they misdiagnosed this problem as a need for a new BB, and maybe the new BB wasn't necessary. I'm not asserting that last point as the truth, but an unnoticed non-square hole could be the cause of the crank falling off, in which case, insufficient torquing was not the cause.

Here is something I don't know: is it possible to tell if the hole was square before the accident?
@FBinNY, I still haven't used a torque wrench or a tensiometer, but I have no objections when a mechanic uses one.
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Old 08-04-14, 05:10 PM
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Originally Posted by noglider View Post

Here is something I don't know: is it possible to tell if the hole was square before the accident?
...
With a trained eye, it's possible to see loose crank damage before installing. OTOH, once it's installed and ridden, I doubt it would be possible to know if it had been damaged previously.
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Old 08-04-14, 05:18 PM
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I suppose in either case, the bike shop is remiss. They should have torqued it right. If they did, then the probes was caused by damage they should have noticed.

i disagree with you about anger and aggravation. I think it's unprofessional. If I were the customer, I would want the owner/manager to say that 1. He is sorry, and 2. He will get to the cause and make sure it doesn't happen again. I don't want to see or be involved in employer/employee drama.
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Old 08-04-14, 07:31 PM
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Originally Posted by FBinNY View Post
The use of torque wrenchws on bicycles is a relatively new phenomenon. Not counting a fringe element that confuses bicycles with space vehicles, nobody started using torque wrenches until the advent of carbon parts. That's after the square taper crank was already being phased out on better bikes. In the heyday of Sq. taper, millions upon millions of these were installed and maintained by both pros and amateurs with no serious issues. (Yes, some did work loose, but the numbers are small and consistent with other mechanical issues).

So, maybe younger mechanics that were never properly trained might not know how to properly torque a crank bolt, but the vast majority of mechanics, pro and not, can and do install these reliably time after time.

It's not a question of tools, it's a question of skill, and more important, craftsmanship and care.

BTW- if we continue to foster the ridiculous notion that torque specs have to be looked up for every mundane job, the cost of bicycle repair will increase beyond the reach of most of the public, and we'll be moving to throwaway bicycles.
And yet, we're still faced with the OP's problem which is all too common and easily avoided by using a simple tool.

What's really funny in this context is your signature line about the value of an accurate measurement vs. a thousand expert opinions.
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Old 08-04-14, 07:52 PM
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Originally Posted by Retro Grouch View Post
..
What's really funny in this context is your signature line about the value of an accurate measurement vs. a thousand expert opinions.
You're right, there's a certain irony there. It's different contexts, but the irony is there none the less.
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Old 08-05-14, 03:37 PM
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I gave them a call yesterday and left a message detailing my situation (they were closed) with a callback number. I was surprised that they did not attempt to call back.

I called them again today and spoke to the guy who I consulted with when I brought the bike in. He was totally nonchalant about the whole thing. I tried to be polite and non-accusatory.

"So right after the maintenance the left crank arm fell right off while I was riding."
"Ok?" <silence>
"Yeah, well, you guys put a bottom bracket on it and then a component that connects to the bottom bracket falls off"
"Bring it in."
"Well, I was wondering what you thought about it" (I'm a few towns away so I wanted to get some info on what they might do before I took the long trip up... maybe a discount, or a free fix, or a possible explanation, or an apology?)
"I can't do anything without looking at the bike."
"Well, do you think it is a bit unusual that a week after the maintenance the crank arm falls off?"
"Bring it in."
"Uh, ok. Thanks, bye"
<click>

I was blown away by his snobbishness. He definitely doesn't care about his customer's satisfaction. He won't say anything until I drive the lengthy trip up to the shop so he can "look at it". Well I already paid him to "look at it". The phone call telegraphed his disposition towards me and based on that I think any hope of repairing this situation without additional cost to me is null. Curiosity makes me want to head up there just so I can pry at him and see what he says back. If I want to get riding again I feel I should find a new shop. From the posts here it sounds like possibly the crank arm slot is damaged if it loosened enough to fall off. Anyway, I need a trusting set of eyes and these guys aren't it. It's almost too humiliating to go back in that store.

Sounds like it's a trip to a new bike shop and time to write some consumer reviews.
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Old 08-05-14, 03:58 PM
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If I had been in the LBS guy's shoes I would have said, "Sorry to hear that. I'd like to look at it to determine if the problem is something we caused. If we caused the problem, we will take care of it right and once and for all, and we will apologize as well." I would not promise without seeing the bike that we will take responsibility, and I'm pretty sure you weren't asking for that, either. LBS guy probably thought you were.
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Old 08-05-14, 04:27 PM
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Originally Posted by kierkegaards View Post
Hi guys,

Never mind that I wasn't injured, but I don't know too much about bike maintenance. Honestly, that's why I took it to them. To fork over the $150 for parts and labor to get a bike back that worked. So I'm a bit discouraged. I'm posting here to see what you guys would do, and maybe gather some knowledge about bike mechanics so that once I go back to a bike tech I can not look so foolish. I'm wondering if they just did a totally shoddy job or if maybe my crank arms were too old?

Thanks.
I'd insist the shop buy me a new crank because once the taper opens up the arm will never seat right again.
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Old 08-05-14, 04:45 PM
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Originally Posted by kierkegaards View Post
I gave them a call yesterday and left a message detailing my situation (they were closed) with a callback number. I was surprised that they did not attempt to call back.

I called them again today and spoke to the guy who I consulted with when I brought the bike in. He was totally nonchalant about the whole thing. I tried to be polite and non-accusatory.

"So right after the maintenance the left crank arm fell right off while I was riding."
"Ok?" <silence>
"Yeah, well, you guys put a bottom bracket on it and then a component that connects to the bottom bracket falls off"
"Bring it in."
"Well, I was wondering what you thought about it" (I'm a few towns away so I wanted to get some info on what they might do before I took the long trip up... maybe a discount, or a free fix, or a possible explanation, or an apology?)
"I can't do anything without looking at the bike."
"Well, do you think it is a bit unusual that a week after the maintenance the crank arm falls off?"
"Bring it in."
"Uh, ok. Thanks, bye"
<click>

I was blown away by his snobbishness. He definitely doesn't care about his customer's satisfaction. He won't say anything until I drive the lengthy trip up to the shop so he can "look at it". Well I already paid him to "look at it". The phone call telegraphed his disposition towards me and based on that I think any hope of repairing this situation without additional cost to me is null. Curiosity makes me want to head up there just so I can pry at him and see what he says back. If I want to get riding again I feel I should find a new shop. From the posts here it sounds like possibly the crank arm slot is damaged if it loosened enough to fall off. Anyway, I need a trusting set of eyes and these guys aren't it. It's almost too humiliating to go back in that store.

Sounds like it's a trip to a new bike shop and time to write some consumer reviews.
Of course you'll never know until/unless you bring it in, but it sounds like, if the crank is damaged, they'll claim it's not their fault and it must have been there all along. (which in all fairness might be true)

I actually understand their need to see it before commenting, but some sense of "no that shouldn't have happened, and we're sorry about it" would have been nicer than acting like the DMV.

I don't know how far they are, or where others may be, but this sounds discouraging and I'd eat the loss and move on. If the drive is not unreasonable, or there's other errands you can do on the way, I'd go and see what they say and do when you "bring it in".
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Old 08-05-14, 04:58 PM
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Crank arms are cheaper than bad publicity, so if I were in their shoes I'd just replace it. However we indeed don't know that it did not have a problem before (why was it put away?) unless you did some riding without problems before you took it in.
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Old 08-05-14, 06:20 PM
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The bike shop guy on the other end of the phone call is in a no win situation.

He can't make you happy because he can't fix your bike over the phone.
He can't even promise you anything (assuming he has the authority) because he has no way of knowing what's right over the phone.
All he can really do is to suggest you bring your bike back to be evaluated.

I'm guessing he could have done that in a more diplomatic way but I also think your expectations of him at that point in time were not realistic.
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Old 08-05-14, 06:36 PM
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Originally Posted by FBinNY View Post
The use of torque wrenchws on bicycles is a relatively new phenomenon. Not counting a fringe element that confuses bicycles with space vehicles, nobody started using torque wrenches until the advent of carbon parts. That's after the square taper crank was already being phased out on better bikes. In the heyday of Sq. taper, millions upon millions of these were installed and maintained by both pros and amateurs with no serious issues. (Yes, some did work loose, but the numbers are small and consistent with other mechanical issues).

So, maybe younger mechanics that were never properly trained might not know how to properly torque a crank bolt, but the vast majority of mechanics, pro and not, can and do install these reliably time after time.

It's not a question of tools, it's a question of skill, and more important, craftsmanship and care.

BTW- if we continue to foster the ridiculous notion that torque specs have to be looked up for every mundane job, the cost of bicycle repair will increase beyond the reach of most of the public, and we'll be moving to throwaway bicycles.

I always used a torque wrench, even though I'm not a professional, because using the right tool for the job helps you do a professional job. And I've seen professionals in lots of different professions that don't use the specific tool called for a job. Most often auto mechanics. The same mechanics that state they don't need to use torque wrenches, also claim that they don't need the service manual to work on a car, and when something goes wrong after they work on a car, that it's not their fault. And they are always happy to take a look and charge you to fix it again.

I could tighten fasteners by hand, and probably never have a problem. But why take a chance? The few moments it would take to ensure that the work was finished properly is the sign of a professional who takes pride in his work. And that is who I would choose to get work done by. Not the guy who claims he's so good that he can't make a mistake.
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Old 08-05-14, 07:41 PM
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Originally Posted by FBinNY View Post
BTW- if we continue to foster the ridiculous notion that torque specs have to be looked up for every mundane job, the cost of bicycle repair will increase beyond the reach of most of the public, and we'll be moving to throwaway bicycles.
Hardly. It takes less than a minute to lookup an unknown torque spec online which is a negligible $1 at $60 an hour.
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Old 08-05-14, 07:45 PM
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Originally Posted by Drew Eckhardt View Post
Hardly. It takes less than a minute to lookup an unknown torque spec online which is a negligible $1 at $60 an hour.
How many fasteners do you check during a service? I check probably 90%. Looking it up, dialling it into the wrench, putting the right bit on, you just doubled the service time.

- joel
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Old 08-05-14, 07:51 PM
  #24  
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Originally Posted by tomacropod View Post
How many fasteners do you check during a service? I check probably 90%. Looking it up, dialling it into the wrench, putting the right bit on, you just doubled the service time.

- joel
Only clamp bolts I've loosened for cable replacement and for parts I'm installing. Everything else was obviously tight enough to stay that way since it was last re-installed or adjusted years ago.

If dialing up a setting takes too long on your torque wrenches get better ones. I'm fond of my Stahlwille wrenches - squeeze the lock, slide the adjusting knob to the appropriate position, and be happy (split-beam wrenches don't require releasing the tension prior to storage as with conventional micrometer wrenches)

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Last edited by Drew Eckhardt; 08-06-14 at 08:02 AM.
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Old 08-05-14, 07:58 PM
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Originally Posted by noglider View Post
Here is something I don't know: is it possible to tell if the hole was square before the accident?
.
Sure it is. If there was already a problem the old crank arms would have been far too easy to remove.

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