1981 DT175 parts list on Partzilla shows the correct races for all the Enduros and most Yamahas back to 1968 and earlier.
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156-23411-00-00 = Bottom
156-23412-00-00 = Bottom, presses into frame steering head
22F-23412-01-00 = Top, presses into frame steering head
22F-23411-01-00 = Top

Note that the "23412" parts press into frame and the 23411 parts are the ones that go one the triple clamps. Many lists have this wrong.

I noticed a problem with parts list diagram years ago when I was changing races....  later parts list had it right.  DEET also posted a thread on this a few years ago I think. 


 

As MarkT has indicated there are indeed errors in the parts books, and the numbers he gives are, I believe, the ones to use if you are replacing all 4 races. 

I had a machinist type friend stop by and I showed him my situation. He told me that the type of bearing we are using for the head stock are called 'ball thrust bearings'. (Good to know the correct term when I am searching.)

My big problem was that I had measured the ID of the top race as being 26mm, and the stem at that point is 25mm, so a whole 1mm of slop that one can never get rid of. The entire top bearing 'sandwich' measured (roughly) 43mmx26x10mm, so I went searching for a ball thrust bearing measuring 43x25x10mm. Never found one exactly those measurements, but close at 43x25x11mm. I did find that I could obtain these, but a bit pricey (and they were overseas). 

Even though others have had issues with taper roller sets using up too much stem height, allowing the top nut to only catch by a couple of threads, I kept looking, and found these:  Yamaha New K&L Upgraded Steering Stem Shaft Race & Roller Bearing Kit 0163-013 | eBay

At the same time I decided to get one of the OEM top races, 22F-23411-01-00, just to see what it measured. The ID of this piece measures 25mm, not 26mm, so if I wanted to, I could use that new top race and be in business. Nice fit on the stem, eliminating the wobble. Yay.

But, really wanting to use the taper set, I wound up going with them, and I am satisfied. In comparing the bearing dimensions, I got nearly the same values from the OEM 'sandwich' and the new taper set (and note- the K&L set indicates "Upgraded"). The tapers are just a little bit taller. At the top of the neck the race protrudes about 2mm above the frame, but the final nut engaged the stem threads the entire depth of the nut, not just 1 or 2 threads. I am confident the assembly will be safe and work correctly. I may need to add an O-ring on each fork leg if the distance between top and bottom triple clamp leaves the headlight bracket loose, but i have dealt with this before.

The eBay listing gives the measurements of each bearing so one can compare them to what he has on the machine.

I'll attach photos when we are able to do that again.

In the meantime, one could use either the OEM #s MarkT gave us, or the new K&L sets.

Reminds me of a lifetime of that slop problem with yamahas at work where a bike came in for a wof [warrant of fitness] every 6 months & 9 time out of 10 the front end is moving & clicking under braking. Could feel it just at stand still holding front brake on & pushing forward. Bloody annoying & could tighten the head bearings to the point of tight steering but only masked the problem. Problem was that Yamaha had the top cone running on the threaded part of the stem so it eventualy flattened of the thread that would never be used anyway. Bit better calculating in the factory would have sorted it. One of my own bikes i bronzed the adjusting nut to the cone which got around my problem. Can't remember what i then did for the dust cup thing but must've had a plan, or not!!.