Calculating Torque of Spring Actioned Piston

[cutzzzzz]

hi guys, this is my first post (and i am don't know much physics), i have a problem that I've ilustrated in a drawing that i attach to this post. Ok so it goes something like this ... if the spring is compressed manually , when i release it how do i calculate the torque of the wheel?
this is the link to the drawing :
http://i50.tinypic.com/2rfvn21.jpg

 

[cutzzzzz]

can some1 help me with this problem??

 

[Pkruse]

Two equations will be most useful to you. One will be simple Hook's law for the spring. The other you can derive from a simple free body diagram, to show how force at the spring converts to torque to the wheel as a function of angular displacement of the wheel.