Road Cycling - my crank arm fell off!

i just got back into town from a 2-week trip and picked up my bike from the LBS. i had
taken my bike in to get a bit of the steerer tube cut off and new shifter cables put on.
so this afternoon i go out for my first ride in 2 weeks. it was wonderful to be back on
the bike....although my legs did not feel so enthusiastic. anyway, i'm about 10 miles out
and going up a small rise when my left crank arm just separates from that bottom bracket.
my speed was slow enough that i avoided a crash which was the good news. the bad
news was that i had to ride home 10 miles with only one crank arm attached. the crank
arm did not break. it just slid off the bottom bracket spindle as if it was tightened on
properly.

i'm not sure why the mechanic at the LBS would have fiddled with my cranks, but it
would seem like he did. there are only 1800 kms on the bike and i have never done
any lossening of the cranks (DA 7800 cranks btw).....seems a bit strange for a crank
arm to fall off under only a very moderate torque. i'm torn between taking it back to
the shop and asking "what the f&ck?" and just fixing it myself and saving a trip in the
car. no damage was done in the incident other than some superficial scratches to the
crank arm which was dragged (while attached to my foot) for a few meters.

-astrocub

...and the crankbolt?

all of the hardware is still attached to the crank arm. this isn't too surprising
given how DA 7800 cranks go together.

Wow that sucks, call the BS you took it to and ask them what they did. If they did not touch your crank................. wierd that this would happen. You must have been mad as hell riding it back with one crank arm. Look at the bright side, I read that this is how LA trains on his pedaling technique(spinning with one leg).

Would they have adjusted the crankarm to ride it?

Hi:

You should take your bike back to the bike shop and talk to the store manager about the quality of
work they are doing. The fact that you didn't get seriously hurt was pure luck!

What they do is tighten the bolt in the end of the bottom bracket, and forget to tighten the
binder bolt. On every other normal three piece crankset, this is the only bolt that holds the crank arm
on. On the new Shimano, it is only used to take up the bearing play -- but they forget to tighten
the binder bolt. Everything appears just fine until the bolt works loose and the arm falls off.

I had a very similar experience. Back in the spring, I upgraded my DA 9 speed to 10 speed. I first thought
I would do a minimal upgrade and replace the STI levers, Rear Derailer and cogs, but decided to replace
everything including the new crankset. Even though I had originally built the bike up from a frameset and
components, I decided to have the bike shop switch the components so it would be done right.

After my third ride with the new components, the left crankarm fell off. At first I couldn't believe it. My
next thought was just to put the thing back on and forget about it. But the longer I thought about it,
the more upset I got -- it could just have well dropped off on a fast descent. I took it back to the bike
shop, told the manager how unhappy I was with the quality of their work and made them give me a refund for the crankset and put the old crankset back on. After they realized what they had done, they were more than happy to do what I asked.

You should take it back to the shop and make them fix it, just so they are aware of the major
mistake they made. The next time they make this mistake, the rider may not be as lucky as you and I.

Clint

It would be an eccentric mechanic who takes the cranks off to cut a steerer tube and install some cables.

Maybe it was just a coincidence that the bike was worked on recently. When was the last time you retorqued your cranks?

I doubt the LBS touched your crank. If I was a betting man, I'd say that it was a coincidence that it happened when it did.

that was my initial thought....the mechanic likely didn't waste any time to mess with my
cranks or bottom bracket. but i would still expect that the initial installation of the cranks
should hold up for more than a few months. cranks don't generally work themselves loose
on such timescales.

This happened to me also. It happened when I was on a group ride. Fortunately I was going uphill so although I was riding pretty hard I was not going super fast. The bolt that goes into the bottom bracket was missing. The binder bolts were still tight but I'm guessing that when the bolt that goes into the bottom bracket had fallen out the cranks wereworked themselves off. I got back to the bikeshop and put a new bolt back into the bottom bracket. This bolt is tightened with a tool from Simano and is not torqued very hard. Mine came loose after I had been riding the cranks about four weeks. A guy from another bike shop came into the shop I frequent and said that they had seen two of these cranks come off. I make a weekly check of this now.

thanks for the replies. from what i've heard here and what some of my buddies have said, it
seems that the new DA cranks have a tendency to come loose. guess i will have to be more
attentive and make sure things are tight on a weekly basis. i definitely don't want this to happen
when i am flying down some descent or out of the saddle on a climb.

It needs to be tourqued properly. Then you should check it periodically. What ever happened to the good old square taper spindles?

I had this happen to me once. I didn't allign the octalink just right, and after while the crank went loose. This might have not be a fault of your mechanic. The material around the cranks is soft, and can eventually give under pressure. One has to be definitely more careful while installing the octalink than with the square spindle.

Campy still has squares.