Cotter pins: Why? Why not?

[Cyril Haearn]

I had a lot of fun with cotter pins, my Gillott still has them. Are they still used on new machines, if not, why not? Any tips for fitting and removal? Which way round? I think a properly fitted cotter pin is quite serviceable

Why do you love (or dislike) cotter pins?

[iandusud]

Nothing wrong with cotter pins but as cranks have generally gone over to alloy they are not suitable. Tips on fitting: Don't attempt to tighten them by tightening the nut. Knock them home with a suitable weight hammer and use tighten the nut enough to secure the cotter pin. Removal: Ideally use a drift with concave head that fits over the threaded part of the cotter pin. A sharp blow with a hammer should remove it. If it resists you need to to support the crank with a suitable lump of hardwood with a recess for the big end of the cotter pin. Repeat above and it should come straight out. The exception to the above is when the bike has been ridden with a loose cotter pin to the extent that the pin is chewed up. This is when the electric drill comes out! As to which way round you fit them depends on which side of the English Channel you were born.

[531colin]

Heads forwards, always.

[iandusud]

Heads forwards, always.

I know which side of the channel you come from

P.S. You're right

[531colin]

Your bonus question for 10 points is what do you do for a tandem crossover drive?

[mjr]

Do cotter pins have anything to do with cots? Where does the name come from?

[fausto99]

Heads forwards, always.

What does this mean. Nut at the top or nut at the bottom with the crank arm pointing forward?

I've never understood it so I just make sure both sides match.

[iandusud]

Heads forwards, always.

What does this mean. Nut at the top or nut at the bottom with the crank arm pointing forward?

I've never understood it so I just make sure both sides match.

Nut at the top.

[iandusud]

Your bonus question for 10 points is what do you do for a tandem crossover drive?

Depends on who is the stronger rider

[531colin]

As you pedal, the head of the cotter pin leads, the nut trails.
On properly-made cranks you can only insert the cotter pin one way.....and that, really is the answer to the tandem question

[Cyril Haearn]

That is how I fitted them, I thought it was the only way

Are there many different types/sizes?

[tim-b]

Hi

Are there many different types/sizes?

At least two sizes, English and Continental, which have a slightly smaller diameter. You can get longer and shorter tapers too, but don't worry about that because they file down easily. File them to fit rather than hammer them (harder) to fit so that the cranks stay at 180°
Regards
tim-b

[iandusud]

Continental bikes (Peugeot, Motobécane, Gitane etc) always came with the cotter pins fitted with the nut leading.

[Samuel D]

What causes these to come loose? I recall riding bikes with floppy cranks in my childhood. They were maintained by farmers who solved most problems with a hammer, so they may have been abused, but how can you mess up the installation of cotter pins?

[jb]

What causes these to come loose? I recall riding bikes with floppy cranks in my childhood. They were maintained by farmers who solved most problems with a hammer, so they may have been abused, but how can you mess up the installation of cotter pins?

They come lose because either:
They're not in hard enough.
or
The mating surface is stepped or otherwise damaged thus not generating the friction necessary to keep them in place & not enough contact to transmit the torque without deforming the two mating flat surfaces.

They were essentially a cheap & quick way of connecting a boss to a shaft without making an expensive key or spline which of course are a lot cheaper to manufacture these days.