Cotter pins: Why? Why not?

For discussions about bikes and equipment.
Cyril Haearn
Posts: 13538
Joined: 30 Nov 2013, 11:26am
Location: Between the woods and the water

Cotter pins: Why? Why not?

Postby Cyril Haearn » 15 Jun 2020, 3:22pm

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?
Entertainer, intellectual, idealist, PoB
Cycling-of course, but it is far better on a Gillott
We love safety cameras, we hate bullies

iandusud
Posts: 322
Joined: 26 Mar 2018, 1:35pm

Re: Cotter pins: Why? Why not?

Postby iandusud » 15 Jun 2020, 4:07pm

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.

User avatar
531colin
Posts: 12968
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Cotter pins: Why? Why not?

Postby 531colin » 15 Jun 2020, 4:28pm

Heads forwards, always.

iandusud
Posts: 322
Joined: 26 Mar 2018, 1:35pm

Re: Cotter pins: Why? Why not?

Postby iandusud » 15 Jun 2020, 4:30pm

531colin wrote:Heads forwards, always.


I know which side of the channel you come from :D

P.S. You're right

User avatar
531colin
Posts: 12968
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Cotter pins: Why? Why not?

Postby 531colin » 15 Jun 2020, 4:43pm

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

User avatar
mjr
Posts: 15682
Joined: 20 Jun 2011, 7:06pm
Location: Norfolk or Somerset, mostly
Contact:

Re: Cotter pins: Why? Why not?

Postby mjr » 15 Jun 2020, 4:45pm

Do cotter pins have anything to do with cots? Where does the name come from?
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
All the above is CC-By-SA and no other implied copyright license to Cycle magazine.

User avatar
fausto99
Posts: 580
Joined: 19 Sep 2011, 10:06am

Re: Cotter pins: Why? Why not?

Postby fausto99 » 15 Jun 2020, 4:58pm

531colin wrote: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
Posts: 322
Joined: 26 Mar 2018, 1:35pm

Re: Cotter pins: Why? Why not?

Postby iandusud » 15 Jun 2020, 5:06pm

fausto99 wrote:
531colin wrote: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
Posts: 322
Joined: 26 Mar 2018, 1:35pm

Re: Cotter pins: Why? Why not?

Postby iandusud » 15 Jun 2020, 5:09pm

531colin wrote:Your bonus question for 10 points is what do you do for a tandem crossover drive?


Depends on who is the stronger rider :D

User avatar
531colin
Posts: 12968
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Cotter pins: Why? Why not?

Postby 531colin » 15 Jun 2020, 5:10pm

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
Last edited by 531colin on 15 Jun 2020, 5:12pm, edited 1 time in total.

Cyril Haearn
Posts: 13538
Joined: 30 Nov 2013, 11:26am
Location: Between the woods and the water

Re: Cotter pins: Why? Why not?

Postby Cyril Haearn » 15 Jun 2020, 5:11pm

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

Are there many different types/sizes?
Entertainer, intellectual, idealist, PoB
Cycling-of course, but it is far better on a Gillott
We love safety cameras, we hate bullies

tim-b
Posts: 1371
Joined: 10 Oct 2009, 8:20am

Re: Cotter pins: Why? Why not?

Postby tim-b » 15 Jun 2020, 7:01pm

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
~~~~¯\(ツ)/¯~~~~

iandusud
Posts: 322
Joined: 26 Mar 2018, 1:35pm

Re: Cotter pins: Why? Why not?

Postby iandusud » 15 Jun 2020, 8:53pm

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

Samuel D
Posts: 3065
Joined: 8 Mar 2015, 11:05pm
Location: Paris
Contact:

Re: Cotter pins: Why? Why not?

Postby Samuel D » 15 Jun 2020, 9:31pm

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
Posts: 939
Joined: 6 Jan 2007, 12:17pm
Location: Clitheroe

Re: Cotter pins: Why? Why not?

Postby jb » 15 Jun 2020, 9:52pm

Samuel D wrote: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.
Cheers
J Bro