Pedal came off mid-ride today.

Skitzin
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Pedal came off mid-ride today.

Postby Skitzin » Fri Oct 13, 2017 9:34 pm

Hi guys,

Was hoping to get some help with a problem with my bike.

As the title suggests I was mid-ride today and my left pedal came off completely. I have never had this happen to me in all my 28 years on this Earth so was hoping to get some help from the experts so to speak.

In particular, I am interested in how to fix this and stop it happening again and what is the possible cause of this problem. I say this because I have tried to put it back on and tighten it up properly but it still came off a second time today.

Since I cannot post link yets, I link with spaces here below. Just remove them obviously :P
imgur . com / a / FIK9h

eeksll
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Re: Pedal came off mid-ride today.

Postby eeksll » Sat Oct 14, 2017 12:40 am

photos link

It looks like a shimano hollowtech 2 crankset. And the crank has come off :shock: , not the pedal

do you also have this part? it screws into the hole of the second photo after the crank slides on.

are you tightening the side bolts up enough?

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Duck!
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Re: Pedal came off mid-ride today.

Postby Duck! » Sat Oct 14, 2017 12:49 am

As above, that's the crank arm, not the pedal..... It's hard to tell from the photos, but it appears the splines in the crank are intact, so that would be a good thing, but best to have checked in the flesh. The crank coming off would indicate the two clamping bolts were not tightened properly; the tension cap linked above provides the bearing preload on the bottom bracket, but it is the opposed pinch bolts through the butt of the crank arm that secure it.
I had a thought, but it got run over as it crossed my mind.

Skitzin
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Re: Pedal came off mid-ride today.

Postby Skitzin » Sat Oct 14, 2017 2:02 am

eeksll wrote:photos link

It looks like a shimano hollowtech 2 crankset. And the crank has come off :shock: , not the pedal


Okay well for starters, thank you for correcting me :) I am not an expert by any means on any of this stuff so it helps especially if I am in need of parts etc :D

Also thanks for linking the pics for me. I understand anti-spam procedures and all that so thanks :D

eeksll wrote:do you also have this part? it screws into the hole of the second photo after the crank slides on.

are you tightening the side bolts up enough?


So I have had this bike for about 4 years now (bought in Dec 2012) and oddly enough I have never seen it with that on the end at all.

I ordered the bike and had the guy who ran the shop assemble it for me. Now looking at it and seeing a thread inside tells me I am obviously missing this piece entirely.

As for tightening the screws, I did them as tight as I could with a set of Allen keys I was going to try a torque wrench next to try and get it super tight. But part of me wonders if this is only part of the problem due to the missing lock piece you linked.

Duck! wrote:As above, that's the crank arm, not the pedal..... It's hard to tell from the photos, but it appears the splines in the crank are intact, so that would be a good thing, but best to have checked in the flesh. The crank coming off would indicate the two clamping bolts were not tightened properly; the tension cap linked above provides the bearing preload on the bottom bracket, but it is the opposed pinch bolts through the butt of the crank arm that secure it.


Yeah sorry was hard to get my camera to focus on them.

Overall there is no damage to any of the "teeth" on the crank attachment point at present.

The part that came off has some very light shear/scratch marks on the inside. But from inspection, the section that has the scratches has no "teeth" at all and no obvious changes to the shape.

A bit hard to describe, but basically the first 7mm or so of the hole is free of "teeth" on the crank that came off with the rest of the hole having teeth. The minor scratches are in the 7mm section.

eeksll
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Re: Pedal came off mid-ride today.

Postby eeksll » Sat Oct 14, 2017 9:29 am

That part is the pre-load bearing, I don't think its required to keep the crank on.

Is this piece still intact? the shimano docs say this part is used as a safety to prevent the crank from falling off. I can see the part in the photos, it clearly didn't work :?
Image
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Last edited by Mulger bill on Sun Oct 15, 2017 11:22 pm, edited 1 time in total.
Reason: YT embed fixed

tez001
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Re: Pedal came off mid-ride today.

Postby tez001 » Sat Oct 14, 2017 10:44 am

As others have said, when putting the crank arm back on make sure the tab is up in the pic above. When the crank is in, then the plate is pushed in. Before tightening it up, test it to see if the crank come off.

When tightening the bolts, they need to be done up equally and evenly.

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CKinnard
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Re: Pedal came off mid-ride today.

Postby CKinnard » Sat Oct 14, 2017 11:32 am

- always ensure the thread of nuts and bolts are clean before tightening.
- on my bikes, I use loctite on most threads.
- I also use a torque wrench.
- I finger test the tightness of most bolts every 3000-5000km, more often if riding rougher roads.

eeksll
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Re: Pedal came off mid-ride today.

Postby eeksll » Sat Oct 14, 2017 2:11 pm

^ you guilted me into cleaning the threads out properly. The other week when i changed to crankset over I couldnt be bothered cleaning the old grease off of everything properly, it took me 10-15 mins to do it just now :oops:

Testing out that saftey latch/pin just now, it stops the crank going on, but it just doesnt do anything to stop it coming off. I installed it, looked to make sure the pin was in its hole, a slight wiggle of the crank arm and the arm comes off :?

Skitzin
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Re: Pedal came off mid-ride today.

Postby Skitzin » Sat Oct 14, 2017 5:24 pm

Okay after some digging around and questioning my local bike store (not the ones I bought it from) I have solved the issue it seems.

First off, the safety latch/pin is literally used as a guide for the crank. Helps to ensure it is in place and lined up properly. However, it is not an essential piece required.

Secondly, it seems the missing locking pin for the crank is to blame. It basically needs to have a locking bolt torqued up to a few N-m to hold the crank on and prevent it from coming off.

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CKinnard
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Re: Pedal came off mid-ride today.

Postby CKinnard » Sat Oct 14, 2017 11:28 pm

eeksll wrote:^ you guilted me into cleaning the threads out properly. The other week when i changed to crankset over I couldnt be bothered cleaning the old grease off of everything properly, it took me 10-15 mins to do it just now :oops:

Testing out that saftey latch/pin just now, it stops the crank going on, but it just doesnt do anything to stop it coming off. I installed it, looked to make sure the pin was in its hole, a slight wiggle of the crank arm and the arm comes off :?


The stopper plate works in unison with tight bolts to stop the crank arm coming off.
If the bolts are loose, then the stopper plate can flop out of position and be useless.

Research loctite or similar. It is underutilized on bicycles imho. Any bolt/nut combo that requires torquing to a particular degree needs to be kept at that tightness via loctite or similar. Grease doesn't do that.

Because bicycles are such minimalist pieces of engineering, any failure can lead to catastrophic user injury.
Hence, it is all the more important to ensure a bicycle is maintained to a higher level than a car, for instance.
i.e. I could relay countless examples of life changing trauma due to dubious maintenance/set up.
A Brisbane cyclist had his battery pack attached to his stem. It came loose while he was descending at speed, and fell downwards and jammed in between his front wheel and fork, locking the wheel, and throwing him over the handle bars. He now lives and moves in a wheel chair with a high level spinal injury.
In my profession I see the worst of what can happen on a bicycle. But bike shops and bike manufacturers suppress this side of the sport for obvious reasons.

Maintain your bicycles to a high level boys and girls. And if you don't know how, seek out an experienced mechanic, and pay them well.
It will be cheaper than any accident you have due to mechanical failure.

Patt0
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Re: Pedal came off mid-ride today.

Postby Patt0 » Sun Oct 15, 2017 9:31 am

The big plastic bolt and the plate with pin a locating devices as said previously. The pin will supply a brief factor of safety.

The two pinch bolts are securing the arm to the crank. IMO using a torque wrench to a setting can possibly lead to problems. When the arm is fully tight on the shaft, the torque of the bolt will rise sharply. Even with perfect lubrication and alternate tighting of the two bolts, insufficient preload may be applied to the bolts, resulting in failure of the union. The bolts in a clamping situation need to maintain tension under a number of circumstances, not least the elastic interactions between the two bolts. So they are effectively springs.
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