I am in the process of overhauling the headset on a '78/'79 Mexico and since I haven't done one of these in a real long time I thought it best to ask.
The headset is a Colnago, which from reading previous posts I am guessing is an Omas. There were 30 ball bearings on both top and bottom, 1/8 inch in diameter. Does that sound right? My copy of Sutherland's doesn't list Omas headsets.
The headset appears to be in decent shape, at least from my untrained eye. There is a small dark ring around the lower race on the steering tube. It doesn't have any pits that I could notice. Other than that, all the races and cups looked decent. I degreased everything and reassembled it with new grease, then began to adjust it by rotating the forks while lightly hand tightening the upper cup. Then I checked for play by pressing against the dropout, and continued to readjust until the play was negligible.
When the play is virtually gone, the headset feels like it's binding/grinding, and I'm pretty sure it's not supposed to feel like that. I reused the ball bearings, but maybe that isn't a good idea. Maybe I need to get some new bearings and try it out again.
I do have a super record headset I am thinking about using in place of this one but am not sure yet I have a problem.
Thoughts and comments are appreciated.