Having trouble getting bolt out of harmonic balancer..1978 ford courier?

Trying to replace the harmonic balancer, but for some reason, I can't get the bolt loose with anything! Tried using the pipe wrench and prybar deal, WON"T BUDGE! I took a air wrench to it..Nothing.I even tried trying to knock it loose, turning over engine with wrench and pry bar attached. Spent all day with NO results, any idea, what's happening? Other ways to get the bolt loose? I have wd-40 on it now soaking. This is on a 1978 Ford Courier, with a 2.0 engine in it.Thanks.