Mamiya RB 360mm f6.3 - dirty fix.

Maris · Apr 23, 2016

The slow speeds in my ancient Mamiya rb67 360mm f6.3 lens failed and it was obviously the delay escapement gear train was gummed up with old lube. Normally one would extract the shutter, take off the gear train, wash it in solvent and put on a few molecules of new lube, re-assemble, and all would be well. But I couldn't open the lens. Some tiny corroded phillips head screws defeated my best screw drivers. So what to do?

Taking off the front and rear lens groups was easy; just unscrew them like light bulbs. Then put the whole lens barrel assembly in an ultrasonic cleaner with solvent and buzz it until every speck of old lube was washed out. The perfectly clean dry shutter would not work: too much friction. Then soak the whole lens barrel in solvent which has had a generous squirt of WD-40 added. When dried out the lens barrel now has every surface with an ultrathin film of oil on it, shutter blades, iris, slow speed gear train, everything. Friction has been defeated and the slow speeds work fine ... but for how long? A very dirty fix indeed.

shutterfinger · Apr 23, 2016

It will dry out in a month or two and quit. Water Displacement #40 will build up into a sticky goo with repeated use. http://wd40.com/cool-stuff/history
Put some acetone, aka fingernail polish remover, on the stuck screw and try it again after 15 minutes. If that fails put some penetrating oil on it and let it set for an hour or more.

williaty · Apr 24, 2016

There's a product called Kroil Oil that is the most impressive penetrating and corrosion-defeating product I've ever encountered. Put a drop or two on the problem screw and wait until tomorrow. Try it. If stuck, repeat. If you get a week of that and it's not moving, it's never moving. However, anything you put Kroil on WILL have to be fully cleaned after. The stuff will climb it's way up and out of a metal cup and free up everything on your workbench for you if you forget about it for a week. It has the most amazing ability to crawl along surfaces and wet them out fully of anything I've ever seen.

I use a ton of Aero Kroil (Kroil in an aerosol can, I'm a professional mechanic) and quite a lot of the liquid Kroil for soaking really nasty things in.

Maris · Apr 24, 2016

shutterfinger said:
It will dry out in a month or two and quit. Water Displacement #40 will build up into a sticky goo with repeated use. http://wd40.com/cool-stuff/history
Put some acetone, aka fingernail polish remover, on the stuck screw and try it again after 15 minutes. If that fails put some penetrating oil on it and let it set for an hour or more.

shutterfinger, I fear that you are right. This lens I bought as an old cheapie and it dates from the early 1970s. There was some fungus on the glass indicating less than optimum storage. And I tried the penetrating oil giving a couple of days to work: no joy. Then I tried heat from a soldering iron: no joy. The screw heads were wearing out from repeated attempts and I didn't want to be forced to drill them out. Drilling out tiny steel screws from an aluminium barrel is an utter pig. My dirty and probably temporary fix works for now. I'm also shopping for another Mamiya 360mm f6.3 lens.

shutterfinger · Apr 24, 2016

Yes, a drill bit in a pin vise used very carefully still walk. As long as it does not go off center more than a tenth of a millimeter or two all should be good. Still its a pain. I had to drill out the screws holding the shutter blades in place on a Synchro Compur. I think they were 1mm diameter. Turns out the shutter is worn out, luckily the lens fit a Copal perfectly.

paul ron · Apr 24, 2016

i love the gorilla war fare method. im getting a good chuckle from this one... a first for sure.

drilling those tiny screws is a pita. i use a dentist bit in a pin holder. the ball tends to center much better. to get a start takes some practice but the cross helps. start it with a very small bit n work it up.. also i found using a bit of cutting oil help keep the bit cutting more material.

wd will leave a light film of a heavier oil as the light oil component of wd evaporates. that heavier oil is too viscous for running a shutter, especially on the blades. a good light oil is what musicians use on brass instruments sold as trumpet valve oil. its the same stuff camera supply sells as nyoil and recomended by shutter manufacturers to lube.

wash the shutter in liquid camp stove fuel sold as coleman fuel... there are other brands n all are the same.

shutterfinger · Apr 24, 2016

I shake my head when one new to the thread makes a comment about the previous techniques posted then posts one that is just as bad or good depending on ones view.

The OP has an Ultra Sonic Cleaner. He does state he used solvent but not the type. There is a solvent made for ultra sonic cleaners, assumed its what he used. I can attest to 90% Isopropyl Alcohol in an ultra sonic cleaner working as well as a Naphtha/camp fuel bath and is a lot less hazardous.
I may use the diamond bit tip the next time I have to drill out small screws. I happens once every 5 to 10 years so I don't invest in a lot of extra tools but I do have some 1/8 inch shank Dremel diamond bits.

I used a #58 or #59 on the shutter blades and did not go off center. Screws will tighten and hold sufficiently in cameras if no more than 10% of the thread wall is removed. I'm not encouraging carelessness but if it creeps in all is not lost.

Maris · Apr 24, 2016

shutterfinger said:
I shake my head when one new to the thread makes a comment about the previous techniques posted then posts one that is just as bad or good depending on ones view.

The OP has an Ultra Sonic Cleaner. He does state he used solvent but not the type. There is a solvent made for ultra sonic cleaners, assumed its what he used. I can attest to 90% Isopropyl Alcohol in an ultra sonic cleaner working as well as a Naphtha/camp fuel bath and is a lot less hazardous...

I used Shellite aka Coleman Fuel aka Ronsonol that is a magic solvent for hydrocarbons. Yes, it is a scary fire hazard so I set up the ultrasonic cleaner in my back garden at the end of a long power lead. Mercifully there was no Hollywood style orange ball of flame. The final "pickling" liquid was 1ml of WD-40 in a litre of Shellite. The theory is that it's enough to ease friction but not enough to degenerate to gum. Theory is fine but practice rules. I'll post again when (if?) the lens fails.

Theo Sulphate · Apr 24, 2016

Maris said:
... I'm also shopping for another Mamiya 360mm f6.3 lens.

Blue Moon (advertiser on this site) has an RB67 360/6.3 C lens for $200.

They also have a 100-200mm f/5.2 W for $125; I have seen that one in person and it's in very beautiful shape. It comes with a support bracket. I've got primes in that range, otherwise I'd get it.

I'm not affiliated with them in any way, I just check their inventory often.

Also, for the 360/6.3 I believe you need a support bracket so as not to bend the focusing rails.

paul ron · Apr 25, 2016

nooooo dont use the naptha in an ultrasonic cleaner! just soak the shutter in it to remove the wd40 if and when it fails again.

Maris · Apr 25, 2016

paul ron said:
nooooo dont use the naptha in an ultrasonic cleaner! just soak the shutter in it to remove the wd40 if and when it fails again.

Good advice. Years ago I was associated with industrial scale ultrasonic cleaners and nobody used naptha in them. Naptha + ultrasonic is only marginally more effective than just soaking. Apart from the fire hazard the main technical hitch with naptha is its low specific gravity. Dense liquids "hit" harder in an ultrasonic cleaner than light ones. The best one was carbon tetrachloride but that's now very hard to get in gallon quantities.

Mamiya RB 360mm f6.3 - dirty fix.

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