Cross section using Camera Clipping Distance results in very dark model interior New to BSE; new to Blender. 

I've imported a fairly complicated .stp model into Blender and successfully produced some renders using Cycles.

Now I want to produce a cross section of the model to show the detail inside. In the viewport I'm achieving what I want using the Camera Clipping Distance.

Viewport:



When I render the scene, using Cycles, the interior parts which are exposed by the clipping distance are extremely dark, i.e. black.

Render:


I have a sun and couple of hemi lights outside the model. I tried moving a light inside the model but it didn't seem to change anything.

Can anyone help me how to avoid this or how to light the scene correctly.

Thanks!
Make sure light can reach the interior. Use boolean modifier(s) to effectively cut away portions of your model, thus giving a true cross-section.

Example:


Create a new mesh (e.g. cube). 
Add a boolean modifier to object which you want to cut away. Set
mode "Difference". Don't hit apply.
Make the new mesh (1.) the target for the modifier. 
Move the mesh into desired position. Where the mesh overlaps the
object will be cut away.