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File This Cotter Pin?

Old 05-01-12, 07:58 PM
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File This Cotter Pin?

Need to replace some cotter pins and I've never filed new pins before. Can someone take a look and let me know whether the new pin (left) should be filed? The old pin is on the right.

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Old 05-01-12, 08:20 PM
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It will probably have to be filed, but the only way to be sure, and to know how much to file, is to try it.
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Old 05-01-12, 09:41 PM
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The old pin has a larger threaded diameter but a longer filed portion. To me this means that the new pin will "ramp up" much sooner then the old pin. How this effects the fit, the amount of threaded portion that stick out past the crank arm, is any one's guess until they actually trial fit the new one. BITD we did this a few times a day. It's not a science but a fit/file and refit until it works. get a back up pin in case you file too much... Andy.
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Old 05-02-12, 02:56 AM
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From Sheldon-
[h=2]Filing Cotters to Fit[/h] It is commonly necessary to file the flats to fit. To file a cotter, put it in a vise at an angle so that the flat is parallel to the vise jaws. When filing, apply a slight twisting force to the file handle to apply more pressure to the wide side of the flat, to help maintain the correct angle of the flat.
Be careful to move the file in a straight line; it is easy to rock the file as you push it across the cotter, creating a rounded surface instead of the desired flat.
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Old 05-02-12, 10:27 AM
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Agree with all that filing will be necessary. It is important that the flat is just that - flat. Any rounding from rocking the file will reduce the contact area on the axle and affect the pin's ability to do its job. I have a small wood block jig that fits the cotter and guides the file. Match the angle of the old pin as well as you can, but this is less critical than both pins having the same angle.

BTW, the old pin looks pretty good. Why are you replacing it?

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Old 05-02-12, 10:34 AM
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Back in the day Bike shops had a cotter holder to go in the bench vise,
because filing Cotter tapers was just what you usually did.

it should be pre shaped so the nut has sufficient thread to hold it in place
after you tap on the head end to set it . hammer and drift punch.

cotters are made soft, don't pull them into place with the nut.

if the threads were undamaged then they can be reused,
advantage of a cotter press,
vs banging them out.

Last edited by fietsbob; 05-02-12 at 10:38 AM.
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