I can not break loose my crankshaft bolt to remove the lower pully. I've tried breaker bars and impact tools but don't want to snap the bolt off. Any suggestions?

 

spray some PB Blaster (walmart) and see then try the breaker bar method again... there's only one way to find out whether the bolt will break or not and that's by trying to remove it.

Just apply the pressure on the breaker bar slowly and not force all you got at the same time--if you force it, it's easier to twist/snap the bolt.