Abu Mahendra

what are the tell-tale signs that the headset needs replacing?

Andrew R Stewart 

The inability to adjust it so it will rotate without indexing/settling in set positions and also not be loose. The wrench flats no longer allow a wrench to work on it. The threaded race or top nut are stripped (if threaded). Or when you want something else just because. Andy

dedhed

Replaced or regreased/new bearings? Sometimes it just needs to be relubed and/or new bearings

FBinNY 

If you're asking, then you DON'T need a new headset yet.

Headsets are one of those "no news is good news" kinds of things. So feel free to assume all is good until/unless there are signs like difficult adjusting, indexing (often incorrectly called "brinnelling") or some other characteristic that has you wondering what might be wrong.

Abu Mahendra

okey-dokey. thanks...

sunburst

I had a headset that I seemed to be able to adjust on the stand but always got funky on the road. It seemed to loosen up as I rode. I had overhauled it, new grease and bearings, and the races looked fine. As luck would have it, this was the first vintage (or any!) bike I restored, so I was new at wrenching. Turns out it had a problem I never would have solved myself. The "master mechanic" at Mikes Bikes saw that the races had become non-concentric and needed to be removed and re-epoxied to the frame. it's been smooth sailing ever since.

HillRider

If the races had to be epoxied into the frame either the headset or, more likely the frame had been damaged, possibly in a collision.

Press-in headset cups should be a tight friction fit and integrated or zero-stack bearings should never need to be glued in place.

Trakhak

Yes, "re-epoxied" should probably have read "epoxied." I built a steel-road-bike-based hybrid in the mid-'80s that I used for riding single-track trails, and the riding stresses ovalized the bottom of the head tube. I used Loktite bearing mount glue to fill the gap between the head tube and the lower headset cup. Worked fine.

JohnDThompson 

This type of damage is particularly common with TIG-welded frames. Lugged frames have additional thickness from the lugs at each end of the head tube and better resist this type of damage. On lugless frames I've built, I braze a reinforcing ring on each end to the head tube.

sunburst

By the various responses, you guys are obviously way ahead of me in mechanical knowledge. Like I said, this was my first restoration/build (I replaced most parts) and didn't need an obscure problem starting out. Yes, "epoxied" is the word I meant because I'm sure it was NOT epoxied in place when Peugeot built it in '72. Most of my wrenching is on these old bikes (future warning in case I should ring in on any other mechanical topics!). In my collection, a modern bike is from the 80's, but I've even got a couple from the 90's. 7 and 8 speeds, oh my!

fietsbob

Overhaul it and inspect the races and their condition.