Filling a Piston cavity

[lothas]

Hi, I'm a mechanical engineering student and I'm doing a project with SolidWorks. I've been asked to create a piston and find a way to calculate the volume of oil inside the piston at all times.

I've encountered some trouble trying to do so

. I tried using extrude up to body but since it's an assembly composed of many parts, I haven't been able to select the whole thing. How would you do it

 

[SSLaser]

I'm assuming the many parts are the valves, seals, etc. Are all these many parts in a volume that is constant? -the piston doesn't go all the way to the valves, right?


If so, you could figure the volume that is constant, and add it to the volume that varies figured by extruding from the piston surface up to top dead center.