I looked up that kit and found a youtube video. Very odd. Even in the video it barely works. The 'gear' you speak of is the escape wheel. It's extremely important, and as you note completely missing in that clock kit. My solution is unfortunate, I think you need a new clock kit.
Here is a nice pendulum escapement model:http://www.thingiverse.com/thing:1128317
This is the video I found:https://www.youtube.com/watch?v=AKNFYTP0IdI