Stuck cleaning Yashinon-DX f/2 50mm - SOLVED!

[Monkeyfinger]

[edit] I got it loose! And eradicated the fungus!

Dripping acetone on the edge of the screw thread and heating up the metal with hot air caused a capillary action for the acetone to creep in between the screw thread, and the retainer cone screwed right off.
After that I cleaned the glass with 50% white vinegar and 50% water, which destroyed the fungus faster than GAS destroys my wallet.
Extra bonus, I can't see any damage traces from the fungus.

---- Original thread: ----

Hey everyone,

I'm disassembling the front element group of a Yashica Yashinon-DX f/2 50mm lens, the all-black M42 version without any chrome parts or accents. I’m trying to remove a starting fungal infection growing behind the front element but have hit a roadblock and could really use some help.

I easily removed the entire front element group from the lens body, but can’t seem to open the front element group itself. This version of the Yashinon-DX seems to have a different mounting system than most other Yashinon-DX lenses. It was probably produced around 1972–1974 at the end of the Yashinon-DX era, just before the Yashica ML lenses came out. Which could explain it's more modern mounting design.

What I Have Tried:

- Wiggling/pulling the retainer cone (the stepped cone on top) upward.
- Turning the retainer cone (mostly counterclockwise) to check if it’s threaded.
- Trying to use a lens spanner on the notches in the retainer ring below, but the cone is too wide to fit a spanner in.
- Twisting the bottom part of the enclosure.
- Adding a tiny amount of Moebius 8000 oil and later silicone spray at the bottom edge of the retainer cone to help loosen it.
- Carefully warming up the enclosure with a hot air space heater to loosen any adhesive or thread locker.

I don't know what the correct method of disassembly is, so I’ve been careful not to apply too much force.

My Questions:

1. Has anyone here disassembled this version of the Yashinon-DX f/2 50mm?
2. Or has anyone worked on a lens with a similar front group design?
3. Does anyone know if the retainer cone is threaded, press-fitted, or held another way?
4. Are there other steps I should try?

Here is a link to photos for clarity:
https://imgur.com/a/JfXUhBX

[visualopsins]

Welcome Monkeyfinger! Happy you got it sorted. Thanks for sharing with us here.

[calvin83]