Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
When the handlebar comes off completely, look at the part of the bar it was on. Isn't there a hole in the bar?
According to parts diagrams, that hole may have to be aligned with an irregular part of the handle. Perhaps there is a projection on the inside of the handlebar the fits into the hole in the bar, and keeps it in place or helps it to stay on the bar.
Otherwise... does the bar show any scratches where the screws were tightened? on the surface of the bar under where the handlebar goes onto it?
Hi it seems Rus has opted out. I am tech Michael I can help. I see you requested a call. I will send you an offer if you accept that I will call you and we will work over the phone from then on if you like. If not we can do it here like this.
But it will be much quicker by phone I agree;-)