So I created a motion study and all was going well until I inserted a spring into the study. There is a pusher block which pushes a gripping block forward, the problem initially was that a spring is needed to return the gripper block to its start position. When I insert the spring, the gripper block doesn't reach its full forward travel and there is a resultant "overlap" between the contact face of the pusher block and that of the gripper block.
I have tried a number of times to resolve the issue but with no luck. The strange thing was that in a similar motion study of an assembly with the same function but different geometry, there was no problem with the spring.
For further clarity have a look at the clip below.