Pentax 6x7 with a "slow" mirror

[franck]

Hello,

I have a rather old Pentax 6x7 (version without mirror lock-up). I have shot a few rolls with it but the mirror often flips quite slowly and even got stuck half way a couple of times. What I mean by the mirror flipping "slowly" is that it quickly flips half way and then there is some lag before it moves completely up and the shutter is fired. Sometimes up to 1/2 second or something like that. A couple of time the mirror did not flip all the way at all. One time shaking the camera made it finish flipping and the other time I had to press the mirror release button.

I have to add that I have tested with a fresh battery and have the same kind of result. Also, despite the slow mirror, the shutter speeds seem accurate since I have got no surprises on the exposure of the film even when noticing very slow mirror action.

Looking at the mechanism that makes the mirror flip, I am wondering if I could/should do any cleaning and lubrication. Attached are some close-ups pf the mechanism. At first I though that the brownish stuff was rust but it is not, it seems to be some sort of baffling. However, the greenish stuff is much likely copper oxide...

Any idea if it can help to clean/lubricate those visible parts? Is is something worth a try or is it risky?

Cheers,

Franck

 

[flavio81]

Consider yourself blessed. My Pentax 67 would be perfect if it had a gentle mirror. I would be happy to have a small mirror lag just so that mirror vibration is not strong.

I think the problem is purely mechanic -- the mirror goes up by purely mechanical means. The shutter speeds are electronically governed, so that's why the timing is fine. BUT, the whole firing cycle is started by an electromagnet. However, i seriously doubt the electrics are at fault. The rust you see is a clear evidence of a mechanical problem.

But in any case the solution seems easy -- apply one drop (or less) of WD40 to those parts and fire the shutter many times. Note... just a very very small amount of WD40, because you don't want it to drop into the shutter curtains.

 

[Poisson Du Jour]

The mechanical linkages are only part of the problem in older cameras. The mirror is activated by a solenoid linked to the shutter. The chances are when the mirror is becoming lazy, so too is the shutter and by association,the shutter speeds. The old 6x7 bodies are very prone to age-related malaises with solenoids, the resistors governing shutter speeds, winding pawls and increasing frame spacing. A very tiny drop of light machine oil (not WD40, which is NOT a lubricant) could be tried but the lubricant must be very, very small as it can drip off into the mirror box. No other type of lubricant or displacement treatment is used or recommended in the Pentax 6x7 engineering manual. Where govenor solenoids are found to be faulty, it's easier now to replace the entire camera as service is very complex and precise and cannibalising parts from like cameras is not a guarantee of long-term useability.

 

[flavio81]

The mechanical linkages are only part of the problem in older cameras. The mirror is activated by a solenoid linked to the shutter. The chances are when the mirror is becoming lazy, so too is the shutter and by association,the shutter speeds. The old 6x7 bodies are very prone to age-related malaises with solenoids, the resistors governing shutter speeds, winding pawls and increasing frame spacing. A very tiny drop of light machine oil (not WD40, which is NOT a lubricant) could be tried but the lubricant must be very, very small as it can drip off into the mirror box. No other type of lubricant or displacement treatment is used or recommended in the Pentax 6x7 engineering manual. Where govenor solenoids are found to be faulty, it's easier now to replace the entire camera as service is very complex and precise and cannibalising parts from like cameras is not a guarantee of long-term useability.

I don't agree here. Note that i have read the entire P6x7 service manual as well.

- The shutter speeds, all speeds, are electronically controlled, so they are NOT mechanically governed.

- Shutter speed problems are usually caused by dirty contacts on the shutter speed dial, not the resistors or other passive components.

- Shutter curtain problems (i.e. bounce at high speeds) are purely mechanical, not electronic. Adjust shutter curtain brake/tension/etc, just as in any similar camera

- In general the electronics of this camera are reliable.

- Doing service in this camera is NOT complex at all, since it is really a very simple mechanism compared with a professional 35mm SLR, and the components are not packed at all. In fact this is a rather simple camera, having no mechanical governors or clockwork, no special mirror deacellerating mechanism, no in-camera metering, no CPUs, no sensors, no flex connectors, and only ONE solenoid (!!!). Only two switches as well: the shutter speed switch, and the battery check switch.

In fact, i am slightly dissapointed at how simple the mechanism is; if they would have incorporated a mirror slow-down clockwork (like in the Mamiya RB67), they would have had a much smoother camera (!), and if they have chosen to opt for two solenoids, they would have perhaps substantially increased battery life for long exposures.

I don't know who is your camera technician, but if I were you, I would switch technicians!!

- WD40 is a mixture of solvent with very light lubricant. It does have lubricant, but of very low viscosity. But my recommendation of applying WD40 is not to lubricate the thing but to remove rust, gunked grease/lubricant, and thus loosen up the mechanism. A drop of lubricant alone wouldn't be as effective. The Pentax service manual wasn't written to repair a rusted camera...

 

[StephenT]

It's been a while since I have had to go into one of my 67's, but I don't recall that brownish stuff being in there. Certainly not the greenish stuff.

If "I" were going to take a hand to it, I would use a bit of Naptha (think Ronson lighter fluid, I believe Zippo has changed their formulation) applied sparingly with an eyedropper. Once those bearing surfaces are cleaned, then a tiny bit of Nyoil (do a web search for it - it is the only thing that I recall being recommended for a camera oil) applied with a needle oiler. That procedure has worked many times for me in bringing an old neglected camera body back to life. Wonder if that would work on me??

Good luck, and as flavio81 pointed out, the Pentax is not a terribly complicated camera. Figure out what makes it work, figure out what isn't working, then you know what to fix.

 

[franck]

Hi guys,

Thanks a lot for the inputs. I gave it a shot and dropped a tiny tiny amount of WD40 on the oxidized pivot points. As you said WD40 is probably not the recommended lubricant but quite effective at cleaning and loosing stuff. It worked as a charm, mirror flips up much quicker and consistently, these pivots were probably the main cause! great!

The amount of WD40 I put is really small (I just used a needle dipped in WD40). My plan is now to let it do its job for a while and maybe then put a tiny amount of machine oil for a more durable lubrication.

Thanks you very much again!

Franck

 

[flavio81]

Hi guys,

Thanks a lot for the inputs. I gave it a shot and dropped a tiny tiny amount of WD40 on the oxidized pivot points. As you said WD40 is probably not the recommended lubricant but quite effective at cleaning and loosing stuff. It worked as a charm, mirror flips up much quicker and consistently, these pivots were probably the main cause! great!

The amount of WD40 I put is really small (I just used a needle dipped in WD40). My plan is now to let it do its job for a while and maybe then put a tiny amount of machine oil for a more durable lubrication.

Thanks you very much again!

Franck

You're welcome! Another P6x7 brought to life! Yay!

 

[franck]

Hello!

This is a quick follow up two month later. I have shot a few rolls with the camera and I had not had any single problem with it. I noticed shotting outside in the cold that maybe it was a bit slower but nowhere near what it was before and far from getting stuck. Thanks again!

Here is the last roll I have shot with expired color neg film: http://photo.fleurey.com/blog/autumn-roll-with-the-pentax-6x7

Cheers,

Franck

 

[flavio81]

Good, enjoy the huge machine!

 

[shutterfinger]

Water Displacing #40 http://wd40.com/cool-stuff/history
That's what it is a water displacing agent, and the 40th formula worked.
It will dry out in a few months leaving a sticky residue and with repeated use will build up.

I find TriFlow to be a very good oil for cameras. http://www.amazon.com/Tri-Flow-TF21...e=UTF8&qid=1446753732&sr=8-2&keywords=triflow
http://www.amazon.com/DuPont-Non-St...e=UTF8&qid=1446753783&sr=8-10&keywords=teflon
Dry teflon lubricant also works well. It may cause parts to stick when it first drys but slight pressure frees them and they work fine afterwards. I use it on shutter blades and aperture blades mostly.