My Jupiter 8 aperture is frozen

[karlori]

So,

This lens and my Zorki 4 have been in the family for like eternity... I pass a roll trough it every now and then. Today my IIIg arrived and I was contemplating putting my Jupiters on it till the elmar arrives...
So i take my Jupiter 8 (chrome version) and was shocked to find the aperture ring stiff... It has some movement between 2 and 2.8 but after that it gets so stiff that if i try to move it I'll start to unscrew the lens...
Sure I have another one working perfectly but this one came with the Zorki 4 that my grandad and dad used and I want to retain it as a working kit how it was from day one...
Any way I could repair this at home ? I have basic clamps and screwdrivers for camera disassembly but have never repaired a lens except for the canon EF 50 1.8 (some repair 😀 the lens is a lego toy)...

All help would be appreciated...

 

[wolves3012]

Try this:
http://pentax-manuals.com/repairs/j8service.pdf

 

[Sonnar Brian]

The aperture mechanism on the J-8 relies on Grease underneath the ring for stiffness. I have seen it get like glue. The optics module unscrews, as you found out. The aperture ring is held in by a retaining ring with one set screw, and the screw that links the aperture ring to the underlying mechanism. Mark positions before removing, then take the set screw out, retainiing ring off, linkage screw out, take off the aperture ring (more like a cone). clean the grease out, usuallY fixes the problem. Lately, i have been using a little bit of scotch tape over the chrome aperture ring to give some friction for the mechanism.