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More often than not, the cotter pins that secure crank arms to bottom bracket spindles must be filed before they will properly fit.  There is a problem associated with doing this.

If the cotter pins are not filed exactly the same amount and at the same angle, then the crank arms will not be spaced at 180 degree intervals.  Of course, this would not be a problem if we could all afford to take the pins to a local machine shop for professional machining.  However, there is at least one way that I know of that will greatly assist you in getting this task completed without a lot of guess work.


1.0 One smooth flat file and handle
2.0 One small magnet
3.0 One bench vice
4.0 Some “shimming” material


1.0 Pick the cotter-pin up with a magnet.  Ensure that the magnet is placed against the tapered flat on the cotter pin.

2.0 With the cotter-pin held to the underside of the magnet, carefully and securely clamp the pin in a bench vise.  NOTE:  As this stands, you will not be able to file anything off of the cotter-pin’s taper because it will be level with the top of the vice jaws.

3.0 Loosen the vice jaws enough to allow the cotter-pin to be lifted slightly.  Slip two equal thickness THIN shims in between the magnet and the top of the vice jaws.  Carefully tighten up the vice jaws and do a visual check to make sure that all is well.  Now the cotter-pin taper will sit slightly above the tops of the vice jaws.

4.0 Begin filing the cotter-pin taper.  Care must be taken to do this properly as follows:

4.1 Push the file forward with a smooth stroke ensuring to hold the file parallel to the tops of the vice jaws.  As you approach the end of the stroke LIFT the file up and away from the cotter pin (this helps to prevent rounding off the tapers).

4.2 Continue this process until you begin to feel the file slide on the vice jaws (the file will not damage the vice jaws if you are careful).

4.3 Continue doing this until the file no longer feels as if it is cutting the cotter pin taper.

4.4 Using the same two shims, repeat this process for the other cotter-pin.

5.0 Install the crank arms with the newly filed cotter-pins.  Gently tap the cotter-pins into place (do not over-do it as the pins might have to come out for more filing if they do not engage adequately).

6.0 With the cotter-pins temporarily installed, look to see if the pin has reached most of the way through the crank.  The target here is to ensure that the cotter-pin is supported on both sides of the bottom bracket spindle.  Do not go too far, just make sure it is partially engaged.

7.0 Once satisfied that the pin is in far enough and that the crank arm are parallel to each other, support the underside of the crank and cotter-pin assembly and drive the pin in good and tight with a hammer.  NOTE:  Be sure that the assembly is supported or you WILL do damage to the bottom bracket bearings.

8.0 Check to ensure that everything looks good and true, then install the cotter-pin nut and tighten it up.  NOTE:  The nut holds the pin in place.  The nut must not be relied on to pull the pin into place.

9.0 Now ride the bike for a few miles the repeat the pin installation process.  You will notice that the pin can be driven in a bit further.

10.0 Tighten the nut up again and you should be good for quite a while.

Good Luck!
The cotter-pins were guessed at and did not come out exactly parallel on this Holdsworth.
The cranks are perfectly parallel on this Peugeot UO8, thanks to the little trick described above.
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