My left crank fell off...

[[XAP]Bob]

On the way home on Friday I noticed a slight "oddity" in the pedalling action on the left side, but I had a manic weekend and so didn't get to look at the bike over the w/end.

This morning I noticed it again, and it very rapidly got worse, I was about to pull over assuming that the cleat was loose on my shoe or something...
Then my left crank fell off!

clank clank clank on the floor (still attached to my foot of course)

Oops...

Fortunately the plastic cap retained the nut, so I popped the crank back on and looked at my toolkit. I don't have a large enough socket, and my adjustable spanners etc. aren't any good in a crank
Used some pliers to get some tightness on the nut, went on for a mile or so, pulled over retightened.

Then I rested my left foot on the trailer hitch and pedalled one legged (letting my left leg join in on the odd hill) and pulled into a little mechanics (the shop is small, not the mechanic) who had a 14mm socket, and gave it a good tightening.

Up the hill, and the crank is loose again
I'll have to cycle into the lbs at lunchtime...

[vernon]

I think that you will find that your left hand crank is beyond salvation as the tapered fit will have been damaged beyond repair. No amount of tightening will remedy the problem and you'll either have to have the left hand crank replaced or have a new chainset installed if you can not get your hands on a spare left hand crank.

Somewhere I've read that the LH crank is more likely to loosen than the RH crank/chainwheels. There was a complex explanation but I didn't bother reading it all.

I had a similar experience during a 100km Audax ride and I spent four or five kilometers pedalling one legged into Ripon where I had a new chain set installed by Moonglu cycles and I went on to complete the ride withing the time limits.

[[XAP]Bob]

I think that you will find that your left hand crank is beyond salvation as the tapered fit will have been damaged beyond repair. No amount of tightening will remedy the problem and you'll either have to have the left hand crank replaced or have a new chainset installed if you can not get your hands on a spare left hand crank.

Somewhere I've read that the LH crank is more likely to loosen than the RH crank/chainwheels. There was a complex explanation but I didn't bother reading it all.

I had a similar experience during a 100km Audax ride and I spent four or five kilometers pedalling one legged into Ripon where I had a new chain set installed by Moonglu cycles and I went on to complete the ride withing the time limits.

Bother....

Left hand pedal - right hand thread.
Precession is likely to do this, but trashing the crank is bad, it's only done a month, so ~500 miles.

[byegad]

That's why it came loose. You need to recheck torque on all these things after 100 miles or so.

[Mick F]

Yep, your taper has had it. The LH crank is for the bin as it's basically irreparable.

Moral of the story is to check the tightness of the bolts from time to time. Sometimes, they work loose. Perhaps as it's only done 500 miles, it should have been checked after the first few miles.

I had a Campag Record chainset some time ago and a normal socket wouldn't go in, I had to buy one and grind off the outside walls to convert it into a thinner-walled socket to reach the bolt. My Camag Chorus one is an 8mm allen key fitting, so far more convenient.

[Edwards]

A get you home bodge would be to use tin foil wrapped around the end of the spindle.

If you have more time for a better one. Apply a tin layer of grease or Cling film to the axle then put some Araldite or some thing similar into the crank. Push the crank on gently but do not fit the bolt. Once the substance has hardened remove the film and cut any excess away from the bolt hole. Then fit the bolt and tighten.

I changed all of our bike's to the Allen Key fitting so it can be tightened without a socket. As Mick F wrote

[[XAP]Bob]

I shall check the replacement after a couple of hundred miles - never checked that nut before

I'll pedal into the lbs at lunch and see if they have a spare...

[Domestique]

Depending on money situation, bike spec etc before you bin the L?H crank you could always cut up a coke can or similar and put a small piece onto the BB spindle before tightening the crank bolt.
I have done this before and it worked well for me.

[james01]

I'll pedal into the lbs at lunch and see if they have a spare...

Lbs spares bins usually have used LH cranks in perfect condition from bikes which have had chainset upgrades. They may even give you one for nothing

[reohn2]

Depending on money situation, bike spec etc before you bin the L?H crank you could always cut up a coke can or similar and put a small piece onto the BB spindle before tightening the crank bolt.
I have done this before and it worked well for me.

Yep that was my thought too,also you may want to buy a pair of allen nuts for you cranks as an 8mm allen key is easier to carry or borrow should it ever happen again.

[531colin]

I have seen this any number of times with (sorry) cheap stuff with nutted BB axles, but very rarely with better quality stuff with BB axles with bolts. .....WHY?????
Quality of the fit of the square taper?
Quality of the original assembly?
Quality of subsequent maintenance?

It certainly seems to be the case that once the thing has been loose once, the taper is damaged and you wont get it to stay tight, but I have never tried wedging it with bits of Coke can etc..
EDIT its always the left crank...

[fullupandslowingdown]

probablity of the crank falling off is proportional to how far you are from anyone with a socket to fit.
There is something I tried once with an alloy crank and thats carefully file it. If done right then it tightens nicely again but of course about 5mm nearer to the frame which might be a problem if either theres no clearance for it or your legs are sensitive to the difference in distance between right and left.
I can only repeat everyone elses advise. check the tighness often after fitting. Typically no more than 50 miles after first fitting or even sooner if you climb hills, then maybe in another 100 miles then again in another 200 miles. If paranoid like me then carry the socket and bar with you for the first 500 miles.
Moral for future is once you feel that wobble ease right off with that crank until you can retighten as it's easier not to have to file / glue / pad the crank then to go slow for a bit.
A lbs mechanic said he always whacks the cranks on first of all, personally I think the shock however carefully the bike is supported, can cause damage to the bottom bracket bearings, whether this is visible to begin with or not.

[andrew_s]

Fit your square taper cranks tight enough first time, then leave them alone.
Tight enough is as tight as you can get them with tools no longer than the cranks.

If the cranks aren't on tight enough when first installed, freewheeling with the cranks level and with weight on can move the crank on the axle slightly. then when you start pedalling it moves back to the normal position. The slight back and forth movement will eventually cause the crank bolt to loosen. It's usually the LH crank that comes off, and when you are in the habit of freewheeling with the right foot forwards.

Also, repeatedly tightening crank bolts is bad practice as you can end up splitting the crank. The normal slight loosness you will find if you check a crank bolt after a week or so isn't because the bolt is coming out, but because the crank is getting forced a bit further on to the taper.

[[XAP]Bob]

OK - This BB is nutted, not bolted, so I can's switch it for an allen bolt.

LBS very helpful, now I have one silver and one black crank -very stylish
£14 is fine by me - they're helpful enough most of the time that I don't begrudge them a little cash now and again.
When the BB needs replacing I'll be making sure it's bolted.

They did recommend that I check it after a few journeys, saying it was effectively always an early stage failure.
There should be no rotational force on the nut/bolt there, as the taper should be dealing with the rotational force, so it's not a left hand thread. When it gets a touch loose the crank just levers it undone.

A reason it won't do that to the RH crank is possibly that the RH is supported by a spider onto the chainset, so I imagine it won't lever across as badly.


Bob

Note: it took on the order of 4 miles to go from noticeable clunk on pedalling to fallen off...

[reohn2]

OK - This BB is nutted, not bolted, so I can's switch it for an allen bolt

Unusual