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Too-Small Cotter Pins?

Old 02-21-23, 02:49 PM
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Too-Small Cotter Pins?

I've been running into a situation that may, or may not be a "situation". I don't have the experience, so asking here.

I have several cottered cranksets, including a few pulled from older Raleighs. I am working on a build and wish to use one of them. However, when I insert a 9.5 mm cotter in an unattached crank or arm, it can pull right through. When I dry fit this on a cotter, it is a bit snugger, but it feels like it COULD be pushed or pulled all the way through.

I've taken these off bicycles myself, and I do not recall the old cotters having their heads seated at/below the surface of the crank arm.

It doesn't appear that bicycle cranksets were ever intended to use cotters wider than 9.5mm, and I am puzzled as to why this is happening. I have measured them with my Park Tool ruler, and yes they are 9.5mm. I've tested with several cotter axles, and it's the same with all the axles that the crank arms fit on. I am wondering if I am missing something. I haven't yet mounted them, and I think they might be okay, but I am not confident.

Is there such a thing as 10mm cotter pins?

Are there only certain BB axles that should be used?

Am I concerned about nothing?

Any help would be appreciated.
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Old 02-21-23, 03:03 PM
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-----

if the heads are disappearing beneath the surface of the arm when fitted and the nominal size is 9.5mm it is likely due to the pin being a very heavy cut

perhaps you could seek out some 9.5mm pins with a medium cut...


-----
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Old 02-21-23, 04:04 PM
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I agree with juvela : I have experienced the “disappearing pin” when I was trying to reuse old (good) pins…. A different cut (and substantial time with a file) solved the problem.
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Old 02-21-23, 08:02 PM
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It seemed rather difficult to locate any 9.5mm cotter pins. How does one locate one and be able to specify the cut?

Then again, I'm trying to visualize this. Struggling to wrap my brain around a slightly different geometry with the same size won't also slide through.
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Old 02-21-23, 09:42 PM
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Originally Posted by USAZorro
It seemed rather difficult to locate any 9.5mm cotter pins. How does one locate one and be able to specify the cut?

Then again, I'm trying to visualize this. Struggling to wrap my brain around a slightly different geometry with the same size won't also slide through.
The pin may slide through with no axle installed but the thicker wedge on a pin with a lighter cut will prevent it from sliding through as the wedge contacts the axle.
I'm sorry, but I have no suggestions for a source for the pins you need.
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Old 02-21-23, 09:46 PM
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In my experience, the cotter pin should slide freely through the crank arm with no axle installed, but with not too much play - say 0.1 to 0.3mm. When properly installed, the non threaded end should protrude 3 - 6mm (based on observation of factory fit cotters).

Last edited by Reynolds; 02-21-23 at 09:50 PM.
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Old 02-21-23, 09:47 PM
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9.5 mm is 3/8 inch. If you search on 3/8 inch cotters, perhaps you will get more results. IIRC French cotters are 9.0 mm, not the ones you want.
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Old 02-21-23, 09:48 PM
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The hole in the crank arm should be big enough for the pin to go all the way through when there is no axle, but the pin should not slide all the way through when the axle is inserted. If you look through the hole in the crank arm with the axle inserted you should be able to see that the axle partly blocks the hole, so a round cotter pin would not possibly go all the way through.

The angled flat on the cotter pin forces the flat on the axle to the same angle, which eventually stops the cotter pin when the fit is tight enough. If the flat on the cotter is filed down too much it will go too far into the hole, but it should never be able to go all the way through.
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Old 02-21-23, 09:54 PM
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Bikesmith appears to still have a couple versions of 9.5 mm cotters.

https://www.bikesmithdesign.com/Cott...s/cotters.html

New cotters from anywhere except Bikesmith are usually filed down too little rather than too much.
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Old 09-26-23, 11:10 AM
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Here's my cotter pin story with my Raleigh Sports (1971). I used the trick of pouring some oil down the seat tube to lube the bottom bracket (BB) bearings ... which worked well for that purpose. Excess oil flowed out the bottom bracket, and between the bottom bracket and the crank arms. No worry, I just cleaned that up,

What I think happened then was that the oil lubed the cotter pins (left side only, so far) enough to get into the cotter pin thread nut and it loosened the nut over time with some riding (a few hundred miles). The pin must have loosened too, just a bit, but enough to deform the face of the wedge / incline (flat) , and then I felt a slight wiggle in the arm. I thought, better replace the pin soon.

Not so easy, since I couldn't find NOS Raleigh pins. But, I measured the diameter of the pin (9.5mm) and decide to purchase a similar pin from https://www.cyclingcolors.com/ because their 9.5mm "clavette de pédalier" looked good because the face of the wedge ("flats") was the full length of the pin. 2 pins for US$10 , with shipping to the US. Not bad!, (available on eBay via seller https://www.ebay.com/str/cyclingcolors

Today I removed the old pin from the left crank arm (it practically slid out, probably due to the oil penetration), and reinserted the new pin (cleaned the outside of the BB and the inside of the crank arm with a rag --- greased the outside of the BB and the full length, including threads, of the new pin). . An excellent fit, but a bit long on the thread side. Not bad enough to warrant cutting the length though.

Here are some photos of the old (original) pin, the new pin, and the crank arm / bottom bracket. I would say this particular pin is suitable for the Raleigh Sports of this generation --- there may be a better fitting pin (still 9.5mm in diameter but slightly shorted and a different wedge face).




Dimensions of the old (original) pin and the new pin

Raleigh Sports 1971 Cotter Pin Replacement

Left side bottom bracket end Raleigh Sports 1971

Last edited by bharrisonb; 09-26-23 at 11:15 AM.
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Old 09-26-23, 06:52 PM
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Originally Posted by USAZorro
It seemed rather difficult to locate any 9.5mm cotter pins. How does one locate one and be able to specify the cut?

Then again, I'm trying to visualize this. Struggling to wrap my brain around a slightly different geometry with the same size won't also slide through.
For the parts, and wealth of wisdom and information, contact Mark Stonich.
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Old 09-26-23, 06:54 PM
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Originally Posted by albrt
The hole in the crank arm should be big enough for the pin to go all the way through when there is no axle, but the pin should not slide all the way through when the axle is inserted. If you look through the hole in the crank arm with the axle inserted you should be able to see that the axle partly blocks the hole, so a round cotter pin would not possibly go all the way through.

The angled flat on the cotter pin forces the flat on the axle to the same angle, which eventually stops the cotter pin when the fit is tight enough. If the flat on the cotter is filed down too much it will go too far into the hole, but it should never be able to go all the way through.
Actually Bikesmith Desigh is owned by Mark Stonich, whom I recommend elsewhere in this thread.
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Old 09-26-23, 07:58 PM
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Originally Posted by bharrisonb
Today I removed the old pin from the left crank arm (it practically slid out, probably due to the oil penetration), and reinserted the new pin (cleaned the outside of the BB and the inside of the crank arm with a rag --- greased the outside of the BB and the full length, including threads, of the new pin). . An excellent fit, but a bit long on the thread side. Not bad enough to warrant cutting the length though.
The problem you describe with the old pin is very common with cotter pins that are not fully seated. You can't tighten a cotter pin sufficiently by tightening the nut - it will strip long before it gets tight enough. The pin must be pressed or hammered into place and the nut put on afterward. No matter how hard you press or hammer the cotter pin into place, you should do it again (pressing or hammering) after you have ridden the bike a few times and then tighten the nut. If not, you will have exactly the same problem again before too long.
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Old 09-26-23, 10:05 PM
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We all should be able to secure the proper pin, slide it in, give it a few taps, then torque it lightly for a perfect set.

But Nope, not me. Even when I have been sure that I have the proper pin I have always had to make adjustments. Maybe it was the spindle, or the crank arm, or the hole itself, I just don't know. Even when I am trying to reuse the original pins, that never come out easy, again.

So I get as close as I can and then tediously take a file to the pin and bring it to the proper size/shape. Often its just a few strokes with a bastard file. It's not hard, but in my mind I should not have to do it.

Remember that the angle of the pin and spindle face are critical. If they are a perfect match then I take down the otter diameter of the pin.

Of course USAZorro you know this already... Ha
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Old 09-26-23, 10:12 PM
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Originally Posted by bharrisonb
...(left side only, so far) enough to get into the cotter pin thread nut and it loosened the nut over time with some riding (a few hundred miles). The pin must have loosened too, just a bit, but enough to deform the face of the wedge / incline (flat) , and then I felt a slight wiggle in the arm. I thought, better replace the pin soon.
What a coincidence. I have readjusted and assisted with the repair of several loosening pins on cottered cranks.

Every one of them was the left side!
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Old 09-27-23, 03:10 AM
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Originally Posted by Road Fan
Actually Bikesmith Desigh is owned by Mark Stonich, whom I recommend elsewhere in this thread.
I concur.
He has a no-nonsense website, part and tools that we need, well-made and good prices.
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Old 09-27-23, 02:32 PM
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Originally Posted by zandoval
What a coincidence. I have readjusted and assisted with the repair of several loosening pins on cottered cranks.

Every one of them was the left side!
It's almost always the left. As a non-engineer, what I understand is that there's far less torque applied to the drive-side spindle/crank interface because the power is directly applied to the chain. The left side transfers all of its power through its crank arm/spindle interface.
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Old 09-27-23, 06:15 PM
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This explanation makes sense. I will also say that every cotter failure I can remember has been on the left, going back to my own first big boy bike in the 1970s.
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