Finally I have an update for this website.
I had an advisory on the MOT for the yoke (headset) bearings on the HN125-8.
Here is a run down of how I fixed it.
This can be carried out on the centre stand, but to release the yoke from the frame you'll need a little extra height. I just used a couple of bricks. This was more than sufficient.
I tried to remove as little as possible in this procedure, so first off I loosened the top most fork clamps (10mm & 13mm) & removed the big nut (I used a 32mm socket. This fitted, but was not correct.) on the top of the yoke. With a bit of wriggling to the handlebars the top yoke released complete with the dials. Beneath this is a large nut which has 4 square indents in it.
This was not very tight & was easily released with a light knock with a screwdriver & hammer. As I unscrewed the weight of the forks pulled down. Holding the wheel up in position here (brick under the front wheel) makes unscrewing a breeze. I found that a cable tie to hold the front brake lever, so that the brake is on most useful. This stopped the front fork assembly rolling away once free from the frame. Be careful that the bearings, which are loose don't drop out onto the floor. My grease was real sticky & none fell, lucky.
At the top is a cone unit that is used to tension the bearings, removing this exposes the loose bearings at the top.
Again these were in a sticky & fairly hard grease.
I spent half an hour or so cleaning the bearings & their seats to bring them up 'like new'.
I had 21 bearings in the top & in the bottom. I used standard 'LM' lithium based grease to repack the bearings. Just enough in the bottom to ensure that the bearings were covered & also wouldn't fall out & about the same in the top.
You might need a second pair of hands to help back in with the fork assembly as I found it difficult to chock the front wheel up while putting it back in to the frame. Once in, I put the top 'cone' over the yoke shaft & on with the large nut which has 4 square indents in it.
I hand tightened this down repeatedly while moving the forks side to side. Initially there was some grinding noises while the bearings seated properly, but once they were fully in position this stopped. I checked for front to back movement & side to side at the very bottom of the forks & tightened the large nut until there was none. Then the top yoke was re-fitted & the big '32mm' nut onto that. I done this up to 30lbs/ft (40nm) which seemed enough to lock the lower nut. Re-tightened the top fork clamps & cut off the cable tie. All seems good, nice and smooth & much more free then it was.