Due to changes to crankshafts composition and liability issues most of us in the US no longer straighten crankshafts. Prior method was the use of a jacking rig that used a modified bolt, an protection sleeve, and back support. The whole jig was mounted to the engine. You simply turn in the jacking bolt while checking the crankshaft straightness by rotating the crankshaft. The jacking was done until the crankshaft no longer wobbled.
Hitting with a hammer of any kind is rough on the bearing surface of the engine if the crankshaft is still in the engine.
