the beef

I'm livid.

Today, I was accelerating out of the saddle through an intersection when suddenly I felt the entire left crank give. In a split second I hit the ground hard at about 20-22 mph. I initially thought it was a really bad case of a derailed chain, but then I looked at my bike and saw the truth: the crank arm had simply fallen clean off. And I don't mean snapped off - I mean that it just FELL off, as if it hadn't even been attached in the first place. Pics: https://imgur.com/a/FdkpB

Onlookers were shocked and made sure I was OK. I wasn't terribly hurt other than bruising and a gash on my shin, but my front Zipp wheel got completely bent.

The thing is, these cranks were only recently installed by my local LBS. As a note, the cranks were used.

Nevertheless, I am highly suspecting that this was mechanic error. I mean, I don't see any signs of obvious part failure. Nothing's cracked or broken. So I don't know how to explain it otherwise.

So - what should I do - and what are my options? I feel very angry, wronged, and frustrated. If this is the bike shop's fault, I want them to pay, and then some. What am I entitled to demand? A cop who was nearby suggested that I should ask them to pay for all the damage, then take them to small claims court if they didn't cooperate.

Suggestions?

edit: Upon closer inspection, I noticed a really strange diagonal shearing pattern that runs around half of the inside of the crankarm hole... does this provide any clues?

At this point, I'm just trying to make sense of what happened, even if I don't end up getting any compensation out of this. It bewilders me and scares me that a crank could just pop off like this, especially when I was in the middle of a busy intersection. The car behind me almost hit me.

Pics: https://imgur.com/a/QKZLr

LowCel 

If you are planning on taking them to court I would recommend having this thread deleted.

Personally, I would have this thread deleted until you talk to the bike shop and find out what they have to say.

the beef

Removed the name of the shop. I don't know, should I delete the thread? Do I even have any chance of getting anywhere if the cranks were used? Also - I'm no expert mechanic, so does anything in the pictures I included look fishy to anyone?

LowCel 

Used crank, no proof that the crank was not "tampered" with after you had it to the shop. I'm not real sure what will happen.

It probably won't hurt anything to keep it opened but if you change your mind let me or another mod/admin know.

Also, forgot to mention, hope you heal up quickly and best of luck with the bike.

the beef

OK, thanks a ton for the help.

10 Wheels

Where did the used cranks come from?

the beef

eBay. I know that doesn't help my case. But even then, has anyone ever heard of cranks just falling off like this?! It seems preposterous.

10 Wheels

My left crank arm fell completely off on a cross country tour at 17 mph.
I use toe clips no straps, so no crash.

I had tools and just put it back on and rode another 2,000 miles.

LowCel 

Unfortunately yes, it happens from time to time.

GP

I've had a crankarm fall off during a ride but it was an FSA crank.

Hartlin

1. Learn to wrench for yourself.
2. Install the crank yourself, correctly.
2. Talk to the LBS.
3. Shave you legs.
4. Attempt to selvage your wheel.

2ndGen

Used crank?
Owner assumes all responsibility if it cannot be proven that it was installer error.
Sorry to hear about the crash. Thanks for sharing. A lesson to all.
BTW: There are lawyers who specialize in cycling related incidents
in the back advertising section of a few cycling magazines.

generalkdi

It happened to someone I know, it was a mechanical error from the LBS and the BIKE was brand new.

the beef

OK - thanks for the helpful replies so far.

Upon closer inspection, I noticed a really strange diagonal shearing pattern that runs around half of the inside of the crankarm hole... does this provide any clues? (and I'm assuming this means my crank arm is kaput, right?)

At this point, I'm just trying to make sense of what happened, even if I don't end up getting any compensation out of this. It bewilders me and scares me that a crank could just pop off like this, especially when I was in the middle of a busy intersection. The car behind me almost hit me.

Pics: https://imgur.com/a/QKZLr

RJM

That damage in the spindle could have happened when it was slipping off, but who really knows.

I would at least let the LBS know, let them know that you aren't all too happy about it. Maybe they will help you out with some store credit or something.

znomit

Find out if it was an actual mechanic or the shop junior.

roccobike

Yes it happens. I'd take it back to the LBS and hope they didn't read this thread before you deleted their name. They can remount the crank arm and use a torque wrench to tighten it and assure the right torque is applied. If it falls off a second time, you've got a defective crank or BB or both and you got stuck. If have to admit it's rare, but with all the bikes I used to flip, probably around 200, I did see this problem twice. In both cases, the crank square taper had been overtorqued so that when it was remounted, it failed.

TWD

the fixing bolt came loose and the arm came off. As to why, it probably wasn't torqued to the correct spec which the shop is responsible. It will be difficult to prove. If you ask them nicely they will reattach the arm and hopefully dish your wheel for you.
I have had similar happen but it was on a POS FSA crank. Shimano stuff just works. I doubt the machine surface you are seeing is a defect but I don't have dura-ace arm to compare

BlazingPedals

The thing is, it could very easily be a 'defective' crank. If the previous user rode it while it was loose, the tapered interface could have been slightly rounded; in which case it won't fit securely on the spindle; and regardless of how much it's torqued down it will wiggle, eventually loosening up again. Like roccobike says, have it installed again with special attention to getting it properly tightened. Then watch it closely. If it goes loose again, throw it away, and the BB too.

Harlan

Guys, he's not riding a square taper crank. It's integrated spindle, external BB.

ruindd

My guess is that the arm was slightly loose, and became more loose as your rode. It finally got to it's 'breaking point' as you neared the intersection. It became so lose that the splines were no longer matched up with each other. So as you pedaled down your down force caused the groves in your "EDIT pictures" as your crank arm carved a new spline as it slid out of place.

There's really only two bolts that are holding on your NDS crank arm. One is more of a cap that goes on the NDS and pulls the two sides of the crank together. This bolt doesn't really hold your crank together as much as keep it in place. I know that sounds odd, but it's just keeping things from sliding apart, it's not compressing anything. The other bolt is the pinch bolt that you can see in your picture HERE. It pinches the arm onto the splines of the crank going through your BB.

I'm fairly confident in saying that they didn't properly tighten the pinch bolt on the crank arm. They didn't properly tighten it by either 1) tightening the pinch bolt before the compression cap, or 2) by unevenly tightening the pinch bolt. I'd guess that they didn't tighten the compression bolt going through the BB before tightening the pinch bolt on the arm. This is like clamping down your stem before adjusting your headset. So instead of 100% of the spines being lined up and engaging each other, you only had 30%-50% engaged. This caused a lot of wiggle, which ended up wiggling your crank arm all the way off.

I could be wrong, but this is my guess based on what I can see.

Edit: Answering your actual question

Since it was a thing that an ordinary cyclist wouldn't notice/check, I think it's reasonable that it's something the LBS should be responsible for. If you want the parts fixed (wheel & new crank) then talk to the shop. If you want more (pain and suffering or punitive damages to teach them a lesson), go talk to a lawyer. I bet an ambulance chaser would listen to you, they're 'free'.

Walter

Have only had square taper come loose on me and they usually creak when they're loose. From what I gather from this thread that's not what the OP has so I don't have much direct experience.

If the shop accepted your payment to install the crank there is an expectation that they did so properly so you certainly have grounds to approach them. Beyond that? I'm not a lawyer and certainly can't even speculate.

garciawork

Dura Ace cranks have two pinch bolts right? You have to tighten them incrementally on my Ultegra's, I'd imagine the same for Dura Ace. They probably tightened one all the way, then the other, and from what a former Shimano mechanic told me was if they aren't tightened according to the directions, things don't always tighten/hold properly. Same for stem cap bolts. I'd imagine that is what happened.

abstractform20

ive had this happen on my 105 5600 crankset. same "mechanics"/tech as the dura ace 7800 (or any 105 and up shimano crankset).

i installed it in a rush, and did not double check my work. i rode probably 40-50 miles before i looked down at my crank arm dragging, still clipped in.

cant say for sure, but id put my money on mechanic incompetence. if they are going to install a crankset, or any component on your bike, they should be aware of obvious physical damages, and warn you ahead of time of possible danger.

abstractform20

after my 105 crankset had that happen, i promptly reinstalled my 7800 crankset to be safe. luckily the 105 crankset survived and is in use again