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very stubborn helicoid
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PostPosted: Thu May 02, 2024 11:40 am    Post subject: very stubborn helicoid Reply with quote

I've got this 1.4 DX yashinon very cheap because the lens was totally locked , I could open it all the way to the helicoid but this one it won't move at all. I've soaked it in acetone to see if it will release hopefully, but I do see lots of residue releasing, could it be some kind of glue? Just checked it out and it is some kind of very very sticky glue

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PostPosted: Thu May 02, 2024 7:11 pm    Post subject: Reply with quote

Well, if it releases and you can remove it all I think there's no need to worry about what it was.

Glue is unlikely but maybe a poor quality grease of which some of the components have polymerised/cross-linked due to long exposure to oxygen? Maybe one of our resident chemists can jump in here? (I am not a chemist but I have seen base oils separated out of helicoid grease turn into a sort of thin "plastic" film in old ROKKOR lenses, a film that even acetone has trouble removing)

EDIT: another (albeit unlikely) possibility is that the original grease had lithium stearate as a thickener (very common), and someone decided to "refresh" the grease by adding some polyurea-thickener-based grease. In general those two don't like each other very much and tend to harden when mixed, although there are exceptions.


PostPosted: Thu May 02, 2024 8:34 pm    Post subject: Reply with quote

RokkorDoctor wrote:
Well, if it releases and you can remove it all I think there's no need to worry about what it was.

Glue is unlikely but maybe a poor quality grease of which some of the components have polymerised/cross-linked due to long exposure to oxygen? Maybe one of our resident chemists can jump in here? (I am not a chemist but I have seen base oils separated out of helicoid grease turn into a sort of thin "plastic" film in old ROKKOR lenses, a film that even acetone has trouble removing)

EDIT: another (albeit unlikely) possibility is that the original grease had lithium stearate as a thickener (very common), and someone decided to "refresh" the grease by adding some polyurea-thickener-based grease. In general those two don't like each other very much and tend to harden when mixed, although there are exceptions.


unfortunately it didn´t work , so i´m planning to soak it in gasoline to see the result , another option would be to heat it, but i´m not sure about it regardin alluminum and brass


PostPosted: Thu May 02, 2024 10:50 pm    Post subject: Reply with quote

Boil it, the temperature won't hurt either metal and the different coefficient of thermal expansion at the same temperature should dislodge it.


PostPosted: Tue May 07, 2024 9:13 pm    Post subject: Reply with quote

well , this very stubborn helicoid won´t realese after resting inside of gasoline, neither after heating it up , so ...i have to come out with new ideas


PostPosted: Tue May 07, 2024 10:58 pm    Post subject: Reply with quote

Tap tap tap...to free the jammed metal surfaces. slap it onto a hard flat surface. try sharp taps around the perimeter. use a tool to tap in direction of thread separation. drill some holes for more grip. But before all that have you tried using two strap wrenches?


PostPosted: Thu May 09, 2024 2:10 pm    Post subject: Reply with quote

I guess , I've used all the options available with no result, unfortunately.