unscrew the bronze screw on the bottum of your zippo "guts."
there will be a long spring attached to this, pull it out.
turn your zippo right side up, and shake it to make sure there is no
flint or anything else in the tube. next drop the flint you cut down the tube.
replace the spring and push it down and screw it in.
it won't be flush with the bottum, but it will close.
put the lighter back together and try it out.
if the wheel doesn't spin, the flint is too big.
you can either cut it down more, or file it down with a metal file and pliers.