OK when I got this old '75 Peugeot the headset went south on the 2nd ride. I opened it up and found no grease and about half the bearings missing. I rebuilt it and it seemed to work for a little while, but it loosens up on almost every ride. I tighten it again, and the cycle repeats ...
I have to admit, I used all 25 bearings in the packet on the lower race. There was still a small gap, so I went for it, even though the LBS advised me to remove one. Could this be the problem? The upper had a retainer clip with maybe a dozen bearings but the LBS mechanic told me to just use loose bearings - I put 24 up there, using plenty of grease in both lower and upper.
I installed upright bars, and it is a single speed, so I have to stand on the pedals and pull on the bars if I need to accelerate or climb, which I imagine is putting some torque on the bars, and stress on the headset. But really, I'm just guessing here.
These old Peugeot headsets have a knurled adjustable upper race, which is easily tighened by hand. Then I use a big ol' honking cresent wrench on the locknut, while holding the race with channel lock pliers. I get it adjusted where it feels right, then 15 minutes into a ride, the front end gets squirrely on me again. Damn.
I've even begun to wonder if I anyone uses loctite.