Removing a bent cotter pin
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subaqua
What’s the point
- Location
- Leytonstone
Invite Patrick and/or Andy around and get them waffling . The pin will remove itself and run away
DaveReading
Don't suffer fools gladly (must try harder!)
- Location
- Reading, obvs
An application of PlusGas won't do any harm.
MacB
Lover of things that come in 3's
- Location
- Farnborough, Hampshire
MP I'd try the other suggestions on here before the hammer and punch, that was my first port of call for the same sort of issue. Promptly followed by one seriously knackered punch(cheap tool) and an even harder to shift pin. They knew how to make tough parts back then, I had to drill it out and it took ages but I think would have been easier without my punch work.
youngoldbloke
The older I get, the faster I used to be ...
A well fitted cotter pin gave one an immense amount of satisfaction 
raleighnut
Legendary Member
- Location
- One of the 'Elite'
I used to like hitting things with hammers too.A well fitted cotter pin gave one an immense amount of satisfaction
The most stupid bit of advice I've come across recently was someone advising that the angle of the flat needs to be 'filed to suit', as long as they're fitted in pairs the angle doesn't matter (within reason) as long as they fit the hole in the crank (btw the cotterpin should pass completely through the hole before the crankarm is fitted to the shaft)
XC26
Senior Member
I can offer some obvious advice and tips based on one stubborn cotter pin job I did recently.
1. Ensure the crank arm is fully supported on something very solid, e.g. a brick. (In the past I just used to hammer away at cotter pins with the bike bouncing on its tyres, wondering why the pins always bent).
2. Ensure the blank end of the cotter pin is NOT supported at all and is free to fall downwards.
3. Some say put the nut loosely on the pin to give more support - I think this is futile on a difficult pin.
4. Strike hard with a heavyish hammer - use a punch or a second small hammer against the pin to protect the rest of the components from accidental damage.
5. OK, so now you've reached the 'oh sh!t, I won't be able to reuse this cotter pin' stage, with the pin now being seriously bent and squidged into the crank arm, it's time for drilling and sawing. I tried some blowlamping but it made no difference.
6. Saw off the top of the cotter pin and punch a suitable dimple in the centre to direct the drill bit.
7. This is where I went wrong. If you're impatient like me, stick the kettle on and take a break. Do not go merrily drilling the pin. I did and discovered that when the drill bit meets the hardened steel BB axle, it wanders off course and begins damaging the soft metal crank arm. You need to drill carefully, starting with small drill bits and keep testing whether to pin will come out, with the usual force, without further drilling.
Good luck.
1. Ensure the crank arm is fully supported on something very solid, e.g. a brick. (In the past I just used to hammer away at cotter pins with the bike bouncing on its tyres, wondering why the pins always bent).
2. Ensure the blank end of the cotter pin is NOT supported at all and is free to fall downwards.
3. Some say put the nut loosely on the pin to give more support - I think this is futile on a difficult pin.
4. Strike hard with a heavyish hammer - use a punch or a second small hammer against the pin to protect the rest of the components from accidental damage.
5. OK, so now you've reached the 'oh sh!t, I won't be able to reuse this cotter pin' stage, with the pin now being seriously bent and squidged into the crank arm, it's time for drilling and sawing. I tried some blowlamping but it made no difference.
6. Saw off the top of the cotter pin and punch a suitable dimple in the centre to direct the drill bit.
7. This is where I went wrong. If you're impatient like me, stick the kettle on and take a break. Do not go merrily drilling the pin. I did and discovered that when the drill bit meets the hardened steel BB axle, it wanders off course and begins damaging the soft metal crank arm. You need to drill carefully, starting with small drill bits and keep testing whether to pin will come out, with the usual force, without further drilling.
Good luck.
