I'm having trouble getting my headset to stay adjusted. It either binds, or is too loose. When I finally get it okay, it seems to loosen on its own after a few days.

I've checked that the bearing cages are correctly aligned, and I think they are.

One thing that isn't obvious to me is the stacking order. I thought I would remember how it was assembled, but perhaps I've got it wrong. The headset is a bit strange in that it has two treaded lock nuts and a keyed washer slash hanger. I can't see what different it would make, but should the washer go between the adjustable race and the first locknut, or between the two lock nuts?

Right now I have it going in this order:
adjustable race, keyed washer, first lock nut, second nut. I've tried it the other way (adjustable, lock not, washer, nut).

Both ways seem to loosen.

One of the nuts is round with notches rather than flat faced; I've found no tool to wrench this, so I've been chewing it up with a pair of channel locks (grrr...)

See pic:

Ditch the second locknut, and use proper spacers.

I've included a photo of my old Trek 950's headset below. I agree that I can't see it making a big difference. Park Tool says
https://www.parktool.com/blog/repair-...eadset-service

Is your upper race threaded? If not, I'd put the mystery threaded washer immediately above that, then the hanger and then top locknut.

As the Park Tool site suggests, check to make sure your top locknut is not grounding out on the top of the steerer threading, but has free space past the end of the threading so it's applying pressure to the whole stack rather than the top of the steerer tube.

Thanks everyone.

Everything but the keyed washer is threaded. Then top nut isn't grounding out. I'm going to give loose bearings a try.

********** Did I miss something? If your weird notched nut is the 3rd threaded item, why not remove it and insert an unthreaded spacer instead as ds suggested?

2 tools missing to do it right ,, VAR headset pliers, and the appropriate headset hook spanner..

bene sugg: a new headset will have the need of a 32mm open end headset wrench ,
and maybe a second one, or a 12" adjustable wrench..

those are more common tools.

headsets last a long time if the adjustment never loosens, and to keep it from loosening
the locknut scheme, 2 nuts tightened against each other, has to be tight.

The problem with your headset is the upper cone (or cup?) has no wrench flats, so you can only lock it finger tight. The keyed locknut isn't your problem, in fact it should help (without the proper spanner you can use a hammer and screwdriver to move it), but you have no way of holding the cone firmly.

Get a headset with wrench flats on the upper cone/cup.

Hmm... the consensus seems to be new headset, and I agree. It is a awkward arrangement.