shutter speed problems on Mamiya RB67 90mm

[Sonicmook56]

Hey gang -

I picked up a Mamiya RB67 kit the other day and included was a 90mm Sekor lens who's shutter only works at one speed. The seller of the camera said it's been like that for a while and needs a spring replaced to make it work.

Can someone point out where this spring might be on this drawing?
http://logojoe.com/RB-RZ/lens-shutter/pages/2004051101.htm

I've taken the lens completely apart already to clean the VERY sticky shutter blades (Can't believe how much junk came off the shutter and aperture blades!) and it now works perfectly - except for the shutter speed select. The selector ring moves freely and clicks where it should. It works correctly at the "T" setting. Any ideas?

I'm very mechanically inclined and love to tinker so I would rather fix it myself instead of sending it out at the risk of screwing it up forever.

Thanks!

 

[John Koehrer]

501-2013 is the part #. Center column, second figure from the bottom.
When you have the selector plate in place there should be a follower that rides along one edge is it there?
If it's trapped beneath the plate I don't think anything will work properly. Something else though. As I remember the slow speed escapement can be adjusted by pivoting it and if it's engaged too deeply it won't allow movement of the blade operating ring.
There are two screws in the escapement one at the end is the pivot & the one near the middle is the adjustment point. For adjustment leave the one at the end snug & try moving the opposite end of the escapement in & out. It won't move much, fractions of a mm perhaps.
For lubrication, watch oil on pivot points on all the levers, a poo dab of grease on sliding surfaces & nothing on the blade housing, blades or blade operating ring. They should be absolutely dry.

 

[Sonicmook56]

Thank you for the reply John.

I must admit I'm a bit nervous about pulling the shutter assembly apart. When I pull the top plate off, will it "explode" and send tiny parts everywhere or do things remain stationary it it's not cocked?

Another option I have is removing a complete working shutter assembly from a 50mm lens I have who's glass is in terrible shape. It appears to be little droplets of something, maybe oil vapor from a CLA gone bad?

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I guess I would like to try and clean the glass before stripping it for the shutter assembly.

How do I get this lens apart? The screws under aperture ring don't come completely out and I feel like I'm using too much force when turning the front element/ floating element ring. it turns a little bit in either direction but nothing seems to be "un threading"

~Ben

 

[John Koehrer]

Ben, the front group is held in by the decorator ring.. That's the one with the lens information on it. Use a rubber stopper from the local hardware put an edge against the ring & it unscrews anti-clockwise.
with regard to disassembly of the shutter, nothing should pop out. I've had detent balls & springs travel quite aways though.

 

[paul ron]

First the lens you are taking the shutter out of has the same flash sync as the one you are putting into? That's generally the difference between shutters on the RB lenses.

RB lenses are opened form the top down. Most need to have the name ring taken out first. The front n rear cells unscrew like light bulbs. Once the cells are out take off the front cone. You'll see a few screws, take em out and take that layer out. Then take the screws out of the next layer and you'll be at the shutter mount.

Then turn the lens over and take out the retaining ring that is around the where the rear cell was. That will drop the entire shutter in it's mount in your hands. To get the mount off, there are 3 screws in the side of the mount that keep it in place. Take off the thin tin part, then loosen the 2 screws, one at each end of the preview slide. The third is the X/M slide spring, a stainless steel flat V shaped piece. The shutter is now free and you cna do what you want with it.

Work in good light. Keep everything organized, screws are put into a pill organizer in the order of operations. Work on a mat so nothing bounces around or mars your lens.

Most of all is have fun n relax. If you feel you are getting in trouble, leave it alone and come back tomorrow when you are feeling fresh again.

Take a look at my pics of lenses on Joe's site. There is an exploded view of one of their early shutters. There are about 5 or 6 variations of shutters so don't think yours is damged because it's missing parts or doesn't jive with the diagram.

 

[Sonicmook56]

Thank you so much for the information and time John and Paul.

I was under the impression that these lenses would sync at any speed?

Well today I did the transplant. The only visible difference in the shutter assembles I could see was a longer post that mechanically couples the shutter speed ring to the actual shutter.. The longer post was a non issue when re-assembling in a different lens.

Also, the 50mm lens the shutter came from was F4.5, where the 90mm is F3.8. All other speeds line up the way they should. This is just glass performance, right? I measured the openings with a pair of calipers and they matched.

Everything feels good and works well off the camera. Can't wait to test the lens with a few rolls of film in the next couple of days.

Is there a way for a DIY'er to measure actual shutter speed or do you just trust what the selector ring says? Listening to the shutters click at slower speeds kinda sound the way they should.

I'll post some more pictures of the lenses in several pieces when I get home tonight.

~Ben

 

[Sonicmook56]

Here are some random shots from my camera phone.

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[Paul Sorensen]

I was under the impression that these lenses would sync at any speed?

They do. I suspect what Paul meant was that the sync system in the shutters is different and can therefore be an issue in swapping one for the other.

 

[John Koehrer]

I note that you're missing a tool from your bench. The 4 lb machinists hammer.