Since this is a forum that is more about technical issues and I think the members are more interested in the inner workings of things, I wanted to share some information about lens rebuilding/cleaning.

Rebuilding/cleaning lenses is not a simple thing to do. The work is physically easy but any small slip up can render the lens unusable. Also, in most lenses if you take the helicals apart and then attempt to put them back together later, the helicals will line up a hundred different ways but only one way will be right. IF you take the helicals apart, be VERY sure that you have marked them somehow or you'll be in for a hard time.

I have been building up a set of manual nikon lenses, primarily AI series lenses. I've been buying cheap lenses that usually have stuck focuses since this is really an easy way to get lenses for less than premium price, as long as you can work on them. This isn't without potential issues as a lot of sellers will tell you the obvious problems but either won't know all of the details or they just won't tell you all the details. Some lenses have even been taken apart previously and put together wrong.. In short, there might be more problems with these lenses than you know about, so be prepared.

Anyway, I can't go into detail about how to rebuild a lens since each lens is different and might need different work done but I can share some of the issues I had.

One of the issues was re-greasing the lens helicals. Tons of websites and forums claim to have the magic formulas for helical grease or they'll tell you that some strange brand works the best. Some sell you tiny little amounts of grease for lots of money while others mention greases that haven't been available for decades.

I've tried a lot of different greases and here's what I found:

Forget any organic grease.

Anything marked NLGI 2 is going to be too thick. This includes pretty much any of the "bicycle" or automobile greases that are touted on a lot of lens websites. They make the lenses feel solid but focusing takes considerable force which may cause the lens to "bob" back and forth while focusing(also known as lens breathing) and/or shift in the mounts. Both of which ruin shots.

NLGI 1 is better but some of the greases are sticky while some are more jelly-like and offer very little metal-to-metal protection. Most of these are made to grease plastic gears or O-rings. A lot of these greases are PAO based oils with thickeners to make them more grease-like.

PAOs are the base chemicals for synthetic oils like Mobil 1 automobile oils. They tend to stick to metals pretty well and they never separate under heat and pressure like organic oils.

Many of the websites I read said nothing about using oils and the few that did said never to use oils. They never specified what kind or even if they had tried it. I found that synthetic motor oil felt the best and offered the most metal-to-metal protection in the helicals. I even performed a test where I heated the lens helicals up to see if the oil would run out. It did not, generally because synthetic oils actually thicken up slightly when heated.

I wanted a PAO based oil with a sticky property that had PTFE(teflon). I found Super Lube 51004. It's a high viscosity PAO based oil with PTFE. a few small dabs of oil on the helicals and the lenses move smoothly and easily with no "whispering" that you get with metal/metal contact. Just don't use too much, a small amount is all that is needed.