if it's really crankcase pressure, pull the oil cap off and see how much effort it is to keep your hand over the oil fill. if it wants to blow your hand off, you might be right. i am not famliar with the ins and outs of 616 crankcase venting, but i've seen gas volvos do the same thing when THEY don't breathe right, pass oil past the ft and rr seals. good luck, chuck.