[.a.t.]

My recently bought SMC K 28mm f/3.5 lens was accurately advertised as having a non functioning aperture. When I took the mount off, I found there was a spring missing. You can see a picture of the spring I need in step 13 of the first post in this thread:
Pentax K 28mm F3.5 Disassembly for cleaning - PentaxForums.com

Luckily, in my spare parts stash I had a spring which might work - if I can get it attached. Here's a photo of my replacement spring and the two posts it needs to connect:




My problem is the pieces are so small I'm having a terrible time trying to manipulate the spring to get it securely fastened to the posts. Can anyone suggest tools or techniques to help me attach the spring?

[marcusBMG]

My usual technique is to get the spring on one post, then stretch it with my starrett screwdriver (or st similar - needle like) and judiciously slide the hook off the end and on to the second post.

[MikeMcE]

Two loops of sewing thread, hook each end and pull until it drops on, cut thread pull one end to remove.you can use tweezers to pull the thread out.


Hang up and DRIVE!

[.a.t.]

. . .

. . .

Thank you for the quick replies. I think one or the other of those methods will help me get the spring on. But a further issue is how to crimp the ends of the spring to keep it fastened to the posts?

Probably it will simply take time and effort to succeed. Perhaps a tweezer might be able to crimp the spring? I should probably buy some sort of magnifying tool / glasses so I can better see what I'm doing. That spring is small!

Does anyone have tips about crimping the spring ends?

[pentaxus]

The ends don't come crimped from the factory. Sometimes they have a small glob of contact cement holding them.

[MikeMcE]

Does anyone have tips about crimping the spring ends?

Proper spring tension should hold them on. You actually want it to pivot on the studs during movement as that keeps the spring from jumping

[c.a.m]

Can anyone suggest tools or techniques to help me attach the spring?

I use the technique described by @marcusBMG, using my Starrett scriber: amazon.com: Starrett 70B Pocket Scriber With Hardened Steel Point, 2-7/8?tag=pentaxforums-20&" Point Length, 3/8" Handle Diameter: Industrial & Scientific

Alternatively, I have mini needle nose pliers (long nose) that is useful for working on small parts. Here's an example: https://www.amazon.com/TEKTON-Mini-Needle-Pliers-PMN01001/dp/B07CP19CKZ/ref=...8861054&sr=8-3 The finer the tip, the better.

Regarding crimping the hooks, I would think that the spring would have sufficient tension to keep the ends in place. Otherwise, a gentle squeeze with the needle nose should work. But don't crimp them tight -- the ends should have sufficient play to allow the spring to move a bit while it is exercised.

- Craig

[.a.t.]

The ends don't come crimped from the factory. Sometimes they have a small glob of contact cement holding them.

Yes, thanks. I've seen that before on some lenses. I'll keep cement in mind as it might be what I need to anchor at least one end.

Proper spring tension should hold them on. You actually want it to pivot on the studs during movement as that keeps the spring from jumping

That makes sense.

. . .
Regarding crimping the hooks. . .

- Craig

Thank you for the links and suggestions, Craig.


I'll give it another try.

[.a.t.]

Woohoo!!
#5020698 rides again!

I'm positively giddy. The lens is back together and it works! It's not good as new, but it's a lot better than it was a few hours ago.

Talking it out here helped me to realize I was making the job harder than it needed to be. When I finally got the mount parts reoriented properly, the process went smoothly. And you guys were right: When I did get the spring attached, the tension was enough to hold it in place.

I used a dental pick to hold the spring while I fitted the ends over the posts / studs. Here's an example of what it looked like (this is a different spare spring):





And here's the actual spring in its new home:






The replacement spring probably isn't as strong as the original because the iris is a bit slow to close down. And it won't stop down beyond f/13. But that's still a lot better than being permanently wide open!

Actually, the lazy iris doesn't matter because this is no longer an auto stop down lens anyway. A former owner cut off the rear aperture lever - likely to avoid it hitting the mirror on a Canon DSLR. No doubt the mount was disassembled in order to try to remove the lever. And that's probably when the original stop down spring went missing.
Unfortunately, there's no (simple) way to non-destructively remove the aperture lever.





So it's a hobbled lens. But I'm sure it'll still be capable of capturing beautiful images.
Many thanks to Adam, Ole and the members here! Without Pentax Forums, I doubt I would've succeeded.
This was a lot more fun than getting socks for Christmas!

[MikeMcE]

Shorten it by a couple of coils to increase tension. Usually slipping a #11 blade in between coils let’s you bend them down, remove 1 coil at a time as needed.


Hang up and DRIVE!

[c.a.m]

Woohoo!!#5020698 rides again!

Excellent!

A former owner cut off the rear aperture lever

Nooo... look away, look away. It's hideous. My eyes... my eyes. Oh well, such is life.

- Craig

[.a.t.]

Shorten it by a couple of coils to increase tension. Usually slipping a #11 blade in between coils let’s you bend them down, remove 1 coil at a time as needed.

Thanks, Mike - but no thanks!
I'm thrilled simply to have the lens back together and, more or less, working. I appreciate the tip, but I'm going to leave well enough alone. If I become fond of the lens, then perhaps I'll consider revisiting the spring.

Excellent!
. . .

Yes! Thanks.

[niceshot]

Thanks, Mike - but no thanks!
I'm thrilled simply to have the lens back together and, more or less, working. I appreciate the tip, but I'm going to leave well enough alone. If I become fond of the lens, then perhaps I'll consider revisiting the spring.




Yes! Thanks.

Cut it to the desired length and the lay over the coil and re-attach. come on you cant leave it half un done can you??

[.a.t.]

. . .
come on you cant leave it half un done can you??

For now, yes.


Edit:
In use, the weak spring became a bother. So I followed the advice of MikeMcE and niceshot and shortened it. The job was easier than I expected, and now the lens stops down fully with only a slight hesitation between f/16 and f/22.