50mm 1.8AIS long nose - repair advice; access to rear elements

[whatdoido]

Hello all

I picked up a 50mm f/1.8AIS long nose with a little fungus and dust.  I am aware, thanks to Richard Haw's site https://richardhaw.com/2020/05/30/repair-nikkor-50mm-f-1-8-ai-s-long-nose/, on how to access to the front elements but one of the bayonet screws has been stripped so can't remove the mount.  I am wondering if anyone has experience of removing the entire optical assembly, INCLUDING the aperture and rear lens block via the front and whether I will face issues re-inserting and realigning the aperture ring coupling and bayonet aperture activation lever?


(c) Richard Haw

The hole at the 3oclock position is where i suspect the aperture activation lever will need to slot through and without the bayonet removed, i dont know how easy it will be to realign everything "blind".  I have serviced a number of my other AI/AIS lenses and some I recall can slide out (maybe the 24mm f/2.8AI?) and reinserting is not too painful.

WIth this specific lens, I have also found with the front optical block removed, unscrewing the front retaining ring for access to front element is impossible - even with acetone and IPA around the base and using rubber grips and even plumber's grips I can't unscrew it!  I worry that the back retaining ring will also be equally well sealed and want to know what else I can try.  If access to rear elements is only available from rear, what if any are my best options to remove the rear retaining ring or should i look to remove the stripped bayonet screw (and how?)

The lens is producing really nice images (a nice surprise) so I'd hate for the fungus to grow and destroy it.

[Erik Lund]

Do you have the appropriate JIS screwdriver the remove the stripped mount screw?
These screws can often be removed by the propper teknik and tool.
You can drill it out and unscrew it with a set of pliers.
These are not valuable lenses, so I suggest finding another less damaged lens will be the easiest,,, unfortunately 

[whatdoido]

Yes thanks, apologies I should have mentioned I do have appropriate JIS drivers 000 I believe (used them successfully for other Nikkor mounts) but not anything specific to deal with stripped screw

The one problematic screw looked like someone had already had a go at it and now is stripped - I was able to remove the other 2 screws (they were tight) and when going at the last one, I did more damage unfortunately.

[Hugh_3170]

Always apply heat to the lens mount screws with a clean soldering iron to soften the thread locker compound that Nikon used back then.

If the damaged screw head is able to receive a straight bladed screw driver - the screw head will be ugly, but sometimes this trick along with the heat from the soldering iron is enough to get the screw moving again.  I have often used a Dremel to create a crude slot for the straight bladed screwdriver.  Sometimes turning the screw driver a little in the opposite (i.e. in the tightening) direction will help break the bond.

Good Luck!

 

Yes thanks, apologies I should have mentioned I do have appropriate JIS drivers 000 I believe (used them successfully for other Nikkor mounts) but not anything specific to deal with stripped screw

The one problematic screw looked like someone had already had a go at it and now is stripped - I was able to remove the other 2 screws (they were tight) and when going at the last one, I did more damage unfortunately.

[pluton]

Alway apply heat to the lens mount screws with a clean soldering iron to soften the thread locker compound that Nikon used back then.

If the damaged screw head is able to receive a straight bladed screw driver - the screw head will be ugly, but sometimes this trick along with the heat from the soldering iron is enough to get the screw moving again.  I have often used a Dremel to create a crude slot for the straight bladed screwdriver.  Sometimes turning the screw driver a little in the opposite (i.e. the tightening) direction will help break the bond.

Good Luck!

This was my thought^^ Create a slot in the remains of the screw head using Dremel. Unless there are tiny small cutting discs for the Dremel, you may also create a slot on the mount metal.  As long as the slot in the mount is shallow, it shouldn't hurt anything.
I'm pretty sure this optic is in one capsule that can be lifted out the front, but it's been a long time since I took mine apart to grease the helicoids and I can't exactly remember.
Added:  It is fairly simple to remove the front rings and check to see if the entire optic is housed in a single capsule.
 

[bressong]

I once undo this lens and Ai 50/1.8 long nose as well.

they are very different on mechnical design except both of them open from front.

the AIS long nose,  the optic group are in two group, mounted on the lens tube, which means, if you remove the front group glass, the rear one still in the lens.

but for the AI version, the entire optics are one piece you can pull it out from the lens tube as the picture show

[whatdoido]

Thanks all.

I've tried the soldering iron (i could feel the chrome ring getting hot) after more IPA and acetone on the head but still not able to do it with the rest of the screw head - next port of call will be to find a dremell/cut down to create a slot.

[Hugh_3170]

Do not be afraid to keep the soldering iron applied to the head of the problem screw for several minutes depending on the capacity of the iron.  I use an 80 watt iron and the lens mount is extremely hot before I apply the screw driver.  You need to get the screw up to around 200 Deg C to properly soften two part epoxy materials, which is what I believe Nikon used to thread lock its older lenses and their lens mount screws.

[whatdoido]

Perhaps a silly question, but would a impact driver or drill be a good way to back out this screw?  I have extractor bits that are small enough for the screw head and I'd think the drill would have enough torque.  Sourcing a small enough dremel to cut a slot is slow

[Hugh_3170]

I suspect that an impact driver has the potential to do more harm than good.  Stick to the heating approach.  Get the offending screw really really hot for as much time as is needed (2 or 3 minutes) and it should screw out.

Is there not enough left of the cross in the head of the cross-head screw to insert a flat bladed screw driver? Often there is enough left.

Perhaps a silly question, but would a impact driver or drill be a good way to back out this screw?  I have extractor bits that are small enough for the screw head and I'd think the drill would have enough torque.  Sourcing a small enough dremel to cut a slot is slow

[whatdoido]

My cheap soldering iron has a max temp of 400oC which I attached the flattest and biggest tip - held it on the head of the screw for about 6-7mins til the chrome grab ring was unconfortable to touch.. but still unable to turn the screw and I think it was totally gone now.

Not to be beaten, I reassessed what i actually wanted to do was get access to the underside of the retaining ring (I didnt care about the bayonet mount really) because i knew it was thread-locked as the collar wouldn't turn to remove the lens elements.  I unscrewed the 3x screws (not thread-locked!!) for the flange (??), popped off flange and had sufficient room to drop acetone and IPA into the right place to soften the seal under the retaining ring and remove the ring and access to the 2x rear elements!  The only concern I had when removing the flange was whether the irus-spring was attached to the underside of the mount but this thankfully was not the case.



You can make out the state of the damaged screw in the bottom right image, where the screw is at the 10 o'clock position.

Hopefully this will help others in a similar position.

[Hugh_3170]

I am glad that you have found an alternative solution to removing the rear lens elements.

Surprising that the heat did not soften the thread locking of the offending screw enough to break the bond.