Lens repair question

[pluton]

To any of our lens service experts, or those with experience with this issue...
Most F-mount manual focus Nikkors I have possessed over the years, including, right now, the 28/3.5K/Ai, 28/2.8 Ais, 35/2.8K/Ai, 50/1.8 Ai, 55/1.2 K/Ai'd, 55/3.5 Micro Ai, 85/1.8 K/Ai lenses, have an annoying thing they do when they are being focused:  When racking the focus ring back and forth during fine focus, the image in the finder moves slightly from side to side.  Brand new Nikkors of this period generally didn't do it, as I recall from 'back in the day'.  But give them a few years of moderate use and the side-to-side jutting action often appears.  Routine CLA jobs have never fixed the issue once it starts.
Q: What causes this?
Q: Is this an issue that can be corrected/fixed during the course of normal CLA lens service?

[richardHaw]

probably a ring or screw inside getting loose and so the objective wiggles around.

[Bjørn Rørslett]

Sounds like the guide rails need to be tightened. These are longitudinal rails preventing the entire lens to rotate when focusing.

Erik can elaborate.

[Akira]

Keith, I think I've had the same experriences with the Nikkor lenses from the same periods.

I think that the loss of the lubrication caused the loose helicoid, and thus the optical axis wobbles when you focus back and forth.  Fresh lubrication should solve the problem.  If you continue to use the lens without lubrication, the helicoid thread will be worn out, which makes the helicoid even looser.

[Erik Lund]

Yes that is the guide rails, and they can all more or less easily be adjusted to perform like new again.

Some lenses are by design adjustable others need a bit of help with a hammer after they have been subject to wear or use like mounting and unmounts filters frequently, for instance the 105mm Ais 2.8 has a front CRC design that has two tiny rails to keep it all in place, not good for heavy filter use

[pluton]

Thank you all for your answers.  I hate the loose feel of dried-up grease in focusing, so in cases where I've purchased an older Nikkor in that condition, I quickly have it lubed.  I have had a fresh grease job reduce, or temporarily eliminate, the cross-axis shifting for a period of time, but it usually comes back.  Good to know there may be a more permanent solution.

[Bjørn Rørslett]

Using a hammer as a "quick repair fix" follows old Nikon traditions. That is the way in which the company adjusted their inventory to avoid taxes in the former days.