Modeling linear or torsion spring in Mechanism

Hello,

I have modeled a cam/follower mechanism for our FIRST robotics assembly and am trying to add a spring in mechanism to return the follower after the cam has rotated.  I have tried both a linear and torsion spring and I can not get either one to work.  Any advice will be apprecaited.  Using Creo 2.

Picutre with cam still in contact:

Photo with cam past contact (springs do nothing).  In this picture both the linear and torsion spring are active, although i would only use one in the real design.

Thank you for any advice.