Help please - I have a crank repair question

tom1209

Member
Hi all, would really appreciate anyone’s advice: Bang in the middle of Tower Bridge last week my left pedal completely detached from my vintage bike (in tact with its long bit). I’ve been racking my brains as to how to reattach but can’t see to get it past where it is in one of my photos I’ve attached. All the advice videos seem to be about the pedal only, whereas for me it’s the arm/lever that has come off. Any advice most gratefully received, thank you!
 

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Cycleops

Legendary Member
Location
Accra, Ghana
Looks like you’ve lost the retaining nut. Just a question of replacing it and you’re good to go, unless you’ve damaged the crank and can’t fully tighten it, which is a real possibility as it’s a soft alloy. A bike shop should have one.
 
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Rickshaw Phil

Overconfidentii Vulgaris
Moderator
Hi @tom1209 and :welcome: to the site.

Looking at your photos what you have is a square taper crank and bottom bracket (crank axle). The crank arm is held onto the bottom bracket by a nut which has worked itself loose and should be hiding behind the silver trim on the crank arm, which will either unscrew or prise out.

The bad news is that with it having come off while you were riding it is possible that the tapered hole in the crank arm will be damaged. If that is the case it's likely to repeatedly work loose again and you'd have to replace it. The good news is that replacements are available. This one looks like it would be a reasonable match: https://www.decathlon.co.uk/p/left-crank-arm-170mm-black/_/R-p-12285?mc=8298276
 
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Hi all, would really appreciate anyone’s advice: Bang in the middle of Tower Bridge last week my left pedal completely detached from my vintage bike (in tact with its long bit). I’ve been racking my brains as to how to reattach but can’t see to get it past where it is in one of my photos I’ve attached. All the advice videos seem to be about the pedal only, whereas for me it’s the arm/lever that has come off. Any advice most gratefully received, thank you!
This is how you do it

View: https://youtu.be/U4UIRPfftKk


A damaged square taper (ST) crank may wobble and not seat properly.
 

iluvmybike

Über Member
Any decent bike mechanic will have box full of 'spare' left side crank arms and find one to match yours as close as possible. If it has been ridden loose until i dropped off then the crank arm will be damaged and useless trying to reit it as it will come off again. It is unlikely that the bottom bracket will be damaged as they are made from steel whreas crank arms tend to be softer alloy and 'give' first
 

Sharky

Guru
Location
Kent
Looks like the head of the crank bolt has been sheered off, leaving the rest of the bolt still screwed in. You'll need to get the bolt unscrewed and removed from the crank, buy a new set of crank bolts and then refit. If you can't get a firm hold on the bolt stub, you may have to replace the bottom bracket as well.
 

Ajax Bay

Guru
Location
East Devon
:welcome:
@Rickshaw Phil has nailed it (and @midlife has provided illustration)
"what you have is a square taper crank and bottom bracket (crank axle). The crank arm is held onto the bottom bracket by a nut which has worked itself loose and should be hiding behind the silver trim on the crank arm, which will either unscrew or prise out.
"The bad news is that with it having come off while you were riding it is possible that the tapered hole in the crank arm will be is damaged."
But the good news is, and @iluvmybike provides the solution: repair to your local bike shop (LBS) with the damaged crank, a decent packet of biscuits and a tenner (max): they will have one(several) the same length. Strongly suspect the nut is lodged behind the 'silver; crank bolt cap (see OP photo - just unscrew or flip that off), but if not ask LBS to rummage for a suitable nut (NB with a flange).
You do not need the tool that @MichaelW2 shares, btw: the crank is already off.
 
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Rickshaw Phil

Overconfidentii Vulgaris
Moderator
Blimey, in all years of riding with square taper, I've never seen cranks like the sugino ones above. Would agree with @midlife , if you can get a replacement nut, would be worth a go.

Good luck
They are fairly common on lower end bikes. My Raleigh and the last two knockabout bikes came with bottom brackets like that. The nut won't have escaped so should be resusable. If I remember right it will need a 14mm socket to either reattach the crank or more likely to fit the new one.
 
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