Bicycle Mechanics - Help

Hi to all.
Yesterday I was tightening the handlebar clamp on my Tassajara and I tightened the vertical bolt too much. I undid it and screwed it in again but now it will only tighten up to a certain limit and then it willgo soft again. The two lateral bolts are ok, and I tried riding the bike without the top bolt and the bike felt ok.
The Bolt I am speaking about is the one that can be seen from above and seems more than a cover than anything else.
Thanks for your help.

That bolt is for adjusting the tension of the steering bearings (headset). It is NOT for tightening the assembly.
In older threaded headsets , a bolt in that position did tighten the stem to the steering tube, but not any more.

Thanks Michael W,
So I guess I do not have to change it?

At this point, I'm assuming that you have brinnelled the bearing races. That's gonna cost you. You really should read up in a good bike maintenance book first-the money you could've saved from this job alone would've paid for it.

Now, when you say that "it will only tighten up to a certain limit and then it willgo soft again", that sure sounds like stripped threads to me.

Were the two lateral bolts already tight when you stripped the compression cap bolt? If so, you may be OK to ride it so until you need to tighten the headset. At that point you'll need to get the star nut and/or bolt replaced.

Once you get the headset tightness set with the compression cap, tightening the two lateral bolts locks the whole assembly tight. As that point the top cap is just there to cover the hole.

As that point the top cap is just there to cover the hole.

and to keep one from losing a chunk of their body when they crash.

Thanks for you help guys