the remainder of the slot and greater than the width of the pin entrance the tapered head allows the lock pin to enter the pin entrance of the lock piston the narrower neck may slide freely within the slot and remains engaged by the wider head and shoulder of the pin as depicted in fig8 the assembly according to one embodiment of the present invention includes a top sub 2 a lock piston 16 having a downhole end releasably insertable in the throat of the top sub a liner hanger 30 for receiving in an uphole end the downhole end of the top sub in a pre deployment arrangement the lock piston may be secured in position within the top sub by shearable screws with further reference to fig8 a first phase in operation of the present invention is assembly of the running tool a top sub may be supplied with a soft seal o ring 46 and may be inserted through the uphole bore of the liner hanger the top sub may be supplied with internal soft seals 48 the pin holes of the liner hanger may be aligned with the pin holes of the top sub the lock piston may be inserted into the throat of the top sub with the collet fingers in a downhole orientation the lock piston may be rotated to align the slots with the holes of the liner hanger and the top sub soft seals may be assembled onto the lock pin the look pins may be inserted through the aligned pin holes in the top sub and the liner hanger in the preferred embodiment having a closed slot design the lock.