I dunno, a two pound lump hammer will tighten one up in a jiffy! Just kidding! Well, no, actually it will, just not usefully. Seriously though, one thing to be sure of is to only tighten the knife with the blades *open* (and wrapped for safety). With the blades open, you have a number of options if you get the pivot too tight -- with them closed, you've got another problem. If you can tighten the pivot up, but it quickly loosens up again, you may need to spread the pivot pin a bit -- one controlled way to do this it to tap a center punch (gently) into the center of the pivot pin (assuming you don't mind the "hole" it will leave behind). A punch modified with a small, rounded tip would be less marring and should work as well.