Nikon AF-S Nikkor 300mm f/4D IF-ED - fungus cleaning

[mfilippa]

Hello, I've seen there are some very experienced people in dismantling lenses here in the forum, so I started this topic.
I've got a copy of this lens, not worn at all, AF working and silent, but with all the 4 groups of lenses infected by fungus.

[mfilippa]

I decided to try and clean it myself. I've got lens spanner, screwdrivers, tweezers, lens sucker, lens blower, rubber cones, isopropyl alcohol, acetone; microfiber clothes, ammonia, hydrogen peroxyde. I am a (hobbyist) microscopist so I'm used to deal with small things, also using a stereomicroscope.
I found the Nikon repair manual and part list of this lens. I studied accurately the drawing, it seems possible to remove all the optics from the front, without disassembly of the mount, diaphragm, helicoids, AF motor and so on.

[mfilippa]

So I removed the front cell (n° 40: refer to the drawing), not easy because it is solidly glued and the only way to put some alcohol in is whith the hood extended, going through with the needle of a syringe.
The problem is the second lens block. It is made of three parts: a sort of frame screwed on the main body, a doublet (4+5) and a retaining ring (46). Some vapor(!) of alcohol has been enough to soften the glue and remove the retaining ring with the spanner, then the doublet with the rubber sucker.
But here I got stuck!
There seems no way to remove the frame (42) from the main body (I painted it orange in this image).

[mfilippa]

I put alcohol repeatedly for one day from the front and tried to unscrew with the lens spanner and the rubber cone: nothing. Tried with acetone: nothing. I put alcohol again and again, nothing. Got somewhat frustrated after some days(!) so I forced a little with the spanner, with the result to scratch the frame (optics were far and safe of course).
I thought that the alcohol maybe could not penetrate between the threads from the front side. The frame has a conic baffle towards the rear of the lens, so I turned the lens upside down, connected a small tube to the syringe and bent it in U-shape. Doing so, operating from underneath, I filled with plenty of alcohol the space around the baffle and let it there one day (look the cyan colour in this image). Tried with spanner and cone, nothing.
Had a glass with the same diameter of the frame, put it in, filled with hot water and waited for 15 minutes. Tried again, nothing.

[mfilippa]

OK, I have searched online and found several disassembly videos and posts for the zooms xx-300, for the AF (non AF-s) f/4 or the older primes f/4.5, but my lens is different.
Just two videos dealing somewhat of this lens: this one https://www.youtube.com/watch?v=tXsG_VYF1Ck is unusable and deal with the AF motor not the optics; and a russian one https://www.youtube.com/watch?v=r4mnGwyxm-8 much more better, but the lens is already opened and when comes at this part, the guy talks about to build a spanner, an then (minute 7:40) he put his hand into the lens and unscrew the whole group with his fingers. I have to say, I do not understand Russian at all. Helpless.

So my doubt is, do I just have been too careful and with some more force it will unscrew, or maybe there are some hint? Some screws not figured into the drawing? Some kind of glue resisting to alcohol and acetone?
Any help would be greatly appreciated.
Thank you

[Nasos Kosmas]

Ciao Fillipa,

Open the captions so can be translated to English or other
Search Richard How site he is a member here,  can lelp you  https://richardhaw.com/
Welcome, nice job!

[Nasos Kosmas]

OK, I have searched online and found several disassembly videos and posts for the zooms xx-300, for the AF (non AF-s) f/4 or the older primes f/4.5, but my lens is different.
Just two videos dealing somewhat of this lens: this one https://www.youtube.com/watch?v=tXsG_VYF1Ck is unusable and deal with the AF motor not the optics; and a russian one https://www.youtube.com/watch?v=r4mnGwyxm-8 much more better, but the lens is already opened and when comes at this part, the guy talks about to build a spanner, an then (minute 7:40) he put his hand into the lens and unscrew the whole group with his fingers. I have to say, I do not understand Russian at all. Helpless.

So my doubt is, do I just have been too careful and with some more force it will unscrew, or maybe there are some hint? Some screws not figured into the drawing? Some kind of glue resisting to alcohol and acetone?
Any help would be greatly appreciated.
Thank you

He build this special tool  that shows on 7:22 and then unscrew with hand

[mfilippa]

Thank you Nasos for your reply.
I landed several times on Richard's site while I search the internet, is a wonderful work! I read all his reports on tele lenses, but no one is similar to AF-S 300 f/4 in this detail.
I have built my own tool, with a plastic hydraulic tube and a steel plate (see photo). This special "wrench" works well, gripping the tags securely and allowing to use force. I put the lens on the floor, put the "wrench" inside, hold it with my feet and turned the wrench. I used force enough to feel pain where the tripod socket push on my ankle, and I just stop.  And, just to be clear, I tried to turn both ways...
Next possible step would be to secure the lens into a vise, provide the wrench with an handle and use more and more torque. But I am not sure that the best would be that, I am afraid to break something.
I still think that if it is too hard, there must be a reason.

[mfilippa]

Open the captions so can be translated to English or other

I tried of course... No help. 

[Nasos Kosmas]

I think you may use acetone, has more dissolve power than alcohol
Send Richard a PM, he may help you

[richardHaw]

I have not worked on this lens yet... I don't think it's difficult to get to that group but you will need special tools. It's very hard to judge because I don't have it in front of me

[mfilippa]

I'm glad you reply to my post, Richard.
I agree it's impossible to say without to see. Here an image showing where I am stuck.
I have to remove the frame into the orange circle. The frame is not so deep into the barrel to be out of reach, either with a current spanner or with my own "special" tool. I tried with alcohol and acetone all around that circle but it's still so tight! It is much tigther than I tink it could reasonably be. So maybe there is some thing I didn't understand.
In the Nikon repair manual is said when reassembly this part to apply "rubber grease". Is it possible that the grease applied in the factory could stop the alcohol to enter the thread? Is it possible the grease had become like a cement in some 20 years...?

[mfilippa]

Maybe I had to put alcohol in the two holes aside the frame...? I'll try

[mfilippa]

It came off!
The holes have nothing to do with it. I put alcohol again from behind and after some hours my self-made tool did the job!
There is something white on the thread (maybe the grease), I'll clean it.
The third group is easy to unscrew... Now I have to build a tool for the 4th group.
Ciao

[richardHaw]

Hello. I'm not sure if you are reading my articles, but if you do... You may have read that I use several types of solvents for nasty parts that won't move
The usual one is alcohol, followed by lighter fluid, then the strongest ones are MEK and acetone

You use them as you go. The white one you see is threadlock and it responds to the best with acetone or MEK.

You must be very careful with your tool, applying downward pressure also helps a lot. If you can drill a crossbar that will help even more