You probably didn't have the seal in all the way and you preloaded the seal instead of the bearing. I teach my guys to measure the amount of thread left from the outer nut. If they are not the same before and after, something is wrong. You might as well put a tapered bearing and cup in while its apart. They are about $35.
If this was case then wouldn't the cotter pin not line up with the hole? I am just asking for my understanding and avoiding future problems. If this not the case then I need to recheck my work.
