Originally Posted by
jackbombay
You need to hit/tap the cotter pin with a hammer as you tighten the nut, with each tap you will get significantly more rotation on the nut.
A cotter press is the preferred way of seating the cotters.
Check the face of the cotter for damage; if it has been ridden while loose, the face can get gouged, which prevents it from seating properly. If you're lucky, the gouge is shallow enough to be filed away; otherwise, the cotter will need to be replaced. This one is terminally damaged:
