How to remove Mamiya RB67 focusing knob?

Hello everyone!

Last weekend I set out to repair a Mamiya RB67 whose shutter cocking lever was jammed whenever holding the camera horizontally. The lever did not spring back after pressing it down, either, so it was pretty clear that a spring must have broken inside.
Long story short – both springs were broken, the one that pulls the lever back up and the one necessary for the part that makes sure that you have to push the lever down all the way first before it comes up again. That part was also the one causing the jam, since it was hanging lose in there.

Now, the problem was that I did not find a way to remove the focusing knob of the camera!
I am attaching a photograph to illustrate the problem. Judging from the repair manual it seems like first you have to remove the round metal plate cover, the one with the two holes, but I could absolutely not figure out how to do it. Tried rotating it, tried levering it out with a screwdriver, nothing worked.
Does anyone happen to know the solution?




By the way, in the end I fixated that lose part with a bit of glue in a position in which it won't get in the way. Now the lever won't jam anymore (although I have to pull it back up by hand). Once I figure out how to remove that focusing knob and then the metal plate underneath that is blocking access to the lever mechanics I want to reattach the springs.

Cheers!
holger

Looking at the service manual the focus knob is attached to the shaft by a nut. Put some nail polish remover/acetone around the inside edge of the knob, let set a few minutes then lift the cover backing plate out via its holes, unscrew the nut which may have thread locker and need a acetone treatment.

that silver cover with 2 holes is held on by some conact cement on the rim of that hollow knob. lift it off, tyen you will see the shaft nut.

Thank you shutterfinger and paul ron!
So the plate is glued in – that explains a lot.
Will try the acetone treatment... and then glue it back in after I'm done, I guess.

Thanks!

you dont need acetone... just lift it.

paul ron said:

you dont need acetone... just lift it.

Click to expand...

Thanks paul ron, that's what I tried without success – to the point of the metal around the holes starting to bend. Had to hammer the edges back in to be level.

Any advice on what tool to use to pull it out?

http://www.cameraeccentric.com/html/info/graflex_9.html
Also an excellent glue remover. I wonder if Paul has ever had a stuck one or one some "technician" used whatever glue they had on hand.
Sounds like some type of solvent is called for.

ive never had any stuck ones but a few stuborn. i wonder if a diy used crazy glue?

the promblem is acetone may eat at the plastic knob. use a hooked dental tool.

perhaps try some alcohol? try diging the point of a utility knife at tge edges? dont worry about scratching, its covered with the leatherete n you can put it back upside down so the cleaner surface is up. sand the damaged areas with an emery nail file.

ive bent a couple n straightend m out with a few taps of a hammer on a flat plate.

btw those holes are used to access screws under the focusing knobs.

Whoever glued that plate in did a pretty good job – there's nothing to scratch off at the edge, but it certainly does look like there's cement or something there.

paul ron said:

btw those holes are used to access screws under the focusing knobs.

Click to expand...

I'm not sure I am following you, Paul. Do you mean there are screws inside the focusing know besides that nut in the center that is indicated in the repair manual?

Guess this weekend I will get some glue remover or acetone and carefully try if I can get the plate off that way. I hope once it is off removing the knob and the metal plate beneath it won't be too much of a problem…

they put those holes so you can get to screws below the focusing knob when removing the side pannels. there are holes in the plastic knob as well so you can put a screw driver through the entire knob.

i dont like to see the plastic knob get ruiened by a solvent. id rather sacrifice the metal plate which you can easily fabricate yourself. just stab a utility knife point in at an edge n lift it.