stiff focusing Mamiya Press 50mm f 6.3 - getting to the helicoid

[neil_grant]

Is it possible to get to the helicoid by removing various parts from the rear of the lens? Namely, the helicoid key and the circlip it's screwed to and also the focusing cam cover? If i can see even a small part of the helicoid i think i can oil it or add a little grease. Anyone tried this or can advise? I don't think i have the skills to take the entire lens apart. Thanks,

[kmac]

I've got one here and I'd be hesitant to disassemble any part of it at all. The helicoil is a little stiff and uneven and it needs lubricating but it will have to stay the way it is, rather than risking harm to the unit. The only remedy I can suggest is to heat it up for a prolonged period. Let it sit in the warm sunlight for a day, working the focus ring now and then. If you do try disassembly, make use of a digital camera to take photos from all different angles of everything as you go, with strong lighting to give adequate depth of field so that all parts and screws etc are in focus. Personally I wouldn't do it though, if everything else on the lens is working satisfactorily, just struggle with the focus ring ... or get a trusted professional tech to work on it.

[orsetto]

Inspired by neil_grant's post in a similar thread:

https://www.photo.net/forums/topic/550432-mamiya-press-lens-problem/#comment-5815810

I looked at the back of my Mamiya Press 65mm and realized the helicoid cap could be removed, revealing the entire threaded circumference without disturbing any of the other mechanics. The rangefinder cam gave me pause until close examination showed its position is not critical, and it can be replaced exactly without fuss. The cam needs to be removed first to completely free the rear baffle cap, which is held by three tiny fragile JIS cross head screws: be sure you do NOT use a typical Phillips screwdriver on these or you will strip the heads. I don't have a proper JIS driver in this size, but years of experience taught me a small Huffy multibit cross head will do the job if used very carefully. Proceed at your own risk, of course.

My results weren't as successful as neil-grants, mostly because I don't have the Marvel oil he specified on hand. At first, a couple tiny pin drops of sewing machine oil did make the seized helicoid turn silky smooth: I was elated. But after re-assembly of the baffle and RF cam, the effect diminished considerably to just slightly improved. Possibly the cap and/or cam exert some mechanical pressure causing drag: I will need to try it again once I lay hands on this Marvel oil. In retrospect, I don't believe its actually necessary to take the rear baffle off: the same amount of thread access is available thru the RF cam slot opening (you just need to keep turning the focus ring to expose a different section to lube). Still, many thanks neil_grant for posting the disassembly idea and Marvel oil suggestion!

Edited March 29 by orsetto

[kmac]

Excellent post orsetto, and as usual from you, very informative and useful. It's prompted me to retrieve my 50mm 6.3 from my cabinet to see if there is actually a niche suitable and large enough for feeding drops of oil onto the very end of the helical. It turns out there is, without disassembling any parts (see photo). The red arrow points to a slot, through which the helical is accessible so tiny drops of oil can be placed on the end of it and allowed to run down, but the focus ring must first be turned to a position to expose the helical .. that position is "1m" or "3.5ft".

A toothpick is too large in diam for the job, which is what I generally use, so a piece of thin wire, slightly bent will work - is my message to the OP.

Using a mini torch, the shiny threads of the helical can just be seen through that slot, but they're off to one side, the outer side, so the lens will need to be angled at 45 degrees while drops of oil are placed in there, one per hour for three or four hours perhaps, and then left over night, after which the focus ring should be turned to start working the oil around. It may take quite some time to achieve easy smooth turning of the focus ring, given that only a tiny drop of oil will be allowed each time, to prevent any from finding it's way to places it doesn't need to be.