Screw the FW nut down so that it is nearly flush with the crank...not flush, mind you, but a couple of thread up. Then take a pair of Vise Grip pliers and clamp on the edge of a fin. Mind you, don't put the pliers across a curved area. That is why it is very important to get right on the edge. Then use a heavy hammer and give it a few raps. I have never had one resist me and and I have never damaged a FW. If it doesn't let go with a 3-4 licks, move the pliers around the FW, check the nut to make sure it hasn't turned, and repeat. If it is really tough you might soak it with PB and maybe even a little heat. I have never needed heat, but I have used PB once or twice. Just take it easy and use common sense.