Originally Posted by
Grand Bois
The angle doesn't matter as long as both cotters have the same angle. The spindle turns to match the angle as the cotter goes in. The reason for filing is to get them to seat at the correct depth.
And as for "correct depth" we are talking mostly cosmetics...
If you use a matched pair of cotters there is no need to file as they should end up automagically 180-degrees apart as long as the cotters are inserted from the correct sides in relation to each other -don't put the nuts on the same side of both cranks and both the heads on the other side. They need to face each other. or away from each other depending on how you look at it. I prefer to put the smooth head facing up on the dirve-side crank when the crank is in the "ahead" position. This makes it smoother and less likely to "catch" your pantleg if you are running a proper chain-guarded bike so you don't need a pants-cincher. But it's not really that big of a deal if you go the other way. I just like to be consistent when I place the cotters.
If you are trying to get away with just using ONE new cotter then you are going to have to do some filing and experimenting to get the cranks to match. Life is too short to mess around with a $2 cotter by filing it. Just replace them both -it's cheap and super easy to do if you have a press.