Originally Posted by GNP77
BMW has a special tool that you thread into this hole and it locks the crank in place to insure it doesn't move from TDC #1 cylinder while you perform your valve adjust. I don't have the BMW tool but made something similar by tapering an M6x 1.25 allen head bolt with the bench grinder.
GNP77 are you sure that this should be an M6 bolt ?! I've just tried to lock the crank, but M6 bolt is too small... I think that this should be an M8!