THey will come apart relatively easily. i always use a crankcase separating tool, obtainable from any decent bike shop (who can get them from MCS, amongst others) and come with a variety of attachments to suit many different bikes. i have seen many a crank damaged by using the old copper hammer trick, it just is not the correct way to do it, even though in a pinch if you are VERY CAREFUL you can do it this way.
