I got a new bike that I assembled myself and I'm having trouble with one part. The handlebar is secured via a quill stem. Basically, you insert the stem into the tube and turn a screw on top of the stem. It causes a little metal thing to press against the tube, securing the handlebar in place. However, it seems like no matter how much I tighten it it always slips out of place. Does that sound like it's defective, or am I just doing something wrong? I was thinking of just epoxying the bitch on, but then I'd never be able to adjust it.