The correct tool for filing a cotter pin for a better fit is the VAR 371 vise. A handy little tool that makes the job of customizing the shape of the pin easy and more profesional. I have two in my shop and use them occasionally, but less and less each year. The Park or VAR cotter press are both reasonably priced and well worth the investment for pressing and removing Cotter pins. I never understood why so many old repair manuals suggested the hammer and wood block method as the preffered method over buying one of those "expensive" presses. I use the press to remove the pin, followed by a drift if the pin is being stuborn. I eyeball the cranks by lining them up with seat tube and replace the pins with the direction of the pins being asymetrical to each other. I use the press to install the pins initially followed by a couple of good wacks with a ball peen hammer and a final tightening of the nuts. This usually lasts 6 months to a year depending on the size and abusive riding habits of the customer.
Robert (dammit jim, I'm I bike mechanic) St.Cyr
ASUCD Bike Barn
Davis, Ca USA