There is a special tool you can get for undo-ing really really tight crank pulley bolts but you're probably not wanting to go and shell out for soemthing you wont really use a lot. Powerbar/socket and a crank on the starter usually works best but make sure you leave a gap so the bar swings a shot way before it gets stopped by the body. You're wanting to to work much like an impact gun
btw, the tool you can get has a 1/2inch drive bit on it which is on an arm probably 4 inches long which is then connected to a much longer arm. You put the socket on and have the arms 90° to each other and bash the top of the longer one with a hammer. Gives you pretty awesome leverage. Haven't has one stuck from using that thing yet. Sometimes need a fair few bashes, but they all come off in the end.
