Thanks! I found that group and exploded it, and used the ctl trick. That seems to have fixed the problems. Where did you find that gap you mentioned, though?

I'm using SketchUp Pro 6.4 on WinXP. In the attached drawing, I can push or pull the outer ring (the one with the holes in it), but when I rotate around to the other side, there's no bottom. When this has happened before (with other drawings), I've usually been able to draw a line across the open space to create a surface closing the "chasm," but here all I get is a thick line and no surface. Something similar, but worse, happens when I try to push/pull the inner gear element. In this case, I only get the exterior volume; none of the gear detail gets extruded, which is what want (along with the aforementioned bottom). What's causing this behavior, and how can I fix it? Thanks.

Geneva2.skp