Leica M6 slow speed issue, design problem ?

[pb908]

my friend lend me his M6 and ask me for help.
he has an issue about slow speed.

the symptom is like this :
- sometimes he get the slow speed looks like 1/50s speed. there are no "rrrr" sound which normaly there if the speed is normal. this issue is randomly appear.
- the issue can be recreated more often if he shoot with the body of camera upside down.

I told him, a normal slow speed shutter behaviour of leica M is :
- when you select slow speed, the escapement assembly will be move in ready position to catch 2nd curtain.
- after the shutter pressed, 1st curtain move all the way, a snap sound can be heard.
- at the end of the 1st curtain travel, it will trigger 2nd curtain to start move/closing. but wait, it is held/catch by the slow speed escapement. you will hear the "rrrrr" sound as the escapement adds a delay.
- once the delay is enough, the slow speed escapement assy "release" the 2nd curtain and it will start to move/closing the film aperture, another snap heard at once it finished.
- then, the slow speed escapement move back to it's ready position, ready for the next exposure.

so in normal camera, during slow speed exposure you will hear :
- snap sound (1st curtain)
- rrrrr (delay)
- snap sound again (2nd curtain)
- another rrrrrr sound

the possibility of my friend case :
1. something dirt inside holding the slowspeed escapement assy not going back to the ready position after the exposure (the 2nd "rrrrr" sound missing).
2. the slow speed assembly FAILED to be in ready position at the time the slow speed is selected (no "rrrrr" sound at all)
3. something else is wrong.

then I open the M6 top cover, actuate the shutter for few times. and my finding :
- all mechanism is clean, move freely, no problem
- the slow speed is engage in the ready position according to the slow speed selected, no problem
- when I turn camera upside down, something moving on the slow speed mechanism. this is the problem.

The slowspeed escapement (as seen in picture below, taken from http://www.jumboprawn.net/jesse/cams/gear-profiles/leica-m2-overhaul/leica-m2-overhaul.html) have a black metal catch lever (bottom right corner)

the black metal lever is the catch which will hold the 2nd curtain during slow speed exposure. as you see, there are 2 metal deck/chassis (top and bottom) holding all assembly together.

another picture from the top (with the Orange color = slow speed escapement catch lever, below the assembly of shutter speed dial area.

and if you see from the side, it will clearly shown that it is engage with the 2nd curtain gear latch. (blue and orange color)

the problem with my friend M6 is that the slow speed escapement catch lever (orange colour) can move up and down around 1mm travel. when it is in UP position, the catch lever (orange) fail to engage with the 2nd curtain segmen gear lever (blue).
as I check the double deck chassis, it is tight, no problem, but as I check the catch lever (orange), there is a tiny gap which is possible for the catch to move up and down.
see picture below (taken with M6 facing at me, area under the RF window)

that's the tiny gap creating the problem (the catch lever in UP (problem) position)

as the camera history, it has never been serviced before. so this makes me wonder if this is a design problem. I never see any of this gap in M3 and M2 I have ever opened.

so, how to fix it ? options :
1. bend the catch lever nose down ==> bad idea
2. add a spacer on top of the gap, but need to keep the catch freely move.
I use option 2, and now my friend M6 is healthy as my other leica.

for you who have m6, can you check the symptom by setting shutter around 1/4s-1/8s and turn camera upside down while you shoot ? let me know if this is leica design issue. hopefully leica give me a free camera for finding this 😀

a search on the RFF tell me this :
http://www.rangefinderforum.com/forums/showthread.php?t=77595

 

[Gabriel M.A.]

for you who have m6, can you check the symptom by setting shutter around 1/4s-1/8s and turn camera upside down while you shoot ?

No problem with my M6 (classic) doing this.

let me know if this is leica design issue. hopefully leica give me a free camera for finding this 😀

Well, you do have a title that will make the speed-readers believe that the M6 has this specific design problem. I'm not a Leica engineer, so I cannot let you know whether or not this is a "Leica design issue", specially because I had it CLAd about five years ago. But I can let you know that I have no problem at the slow speeds (all the way down to B) turning the camera upside down or otherwise.

 

[nobbylon]

Don't bend anything! Before you do anything else, clean the slow speed movement in zippo lighter fluid properly and then lube the bearings with the finest oil you have. Re dip in the lighter fluid and refit.
I've had these symptoms exactly as you describe on around 7 bodies and cleaning the mech cures it.
It fails upside down because the gears sit in sticky bearings due to gravity. I've just had exactly the same on my 2nd M6 body. Just been cleaned out and relubed. Fixed. Now works upside down, side to side diagonally etc etc.
It's actually quite a good test on an M body and one I do when buying to find out if it needs cleaning inside. Set to 1 sec and fire the camera upside down. The first few frames will probably be ok but as the gears settle in the sticky bearings the slow speeds fail if the camera needs cleaning.

 

[rogerzilla]

My, this is hardcore!

I have no answers, but thanks for posting the diagrams.

 

[delft]

My M6 works fine upside-down. If this were a design-fault, the RFF-ers from down under would have noticed it before.
Very impressive technical drawings, by the way

Greetings,

Dirk

 

[chrismoret]

...just utter respect....

 

[maddoc]

... this should become a sticky ! 😀 😉

Don't bend anything! Before you do anything else, clean the slow speed movement in zippo lighter fluid properly and then lube the bearings with the finest oil you have. Re dip in the lighter fluid and refit.
I've had these symptoms exactly as you describe on around 7 bodies and cleaning the mech cures it.
It fails upside down because the gears sit in sticky bearings due to gravity. I've just had exactly the same on my 2nd M6 body. Just been cleaned out and relubed. Fixed. Now works upside down, side to side diagonally etc etc.
It's actually quite a good test on an M body and one I do when buying to find out if it needs cleaning inside. Set to 1 sec and fire the camera upside down. The first few frames will probably be ok but as the gears settle in the sticky bearings the slow speeds fail if the camera needs cleaning.

 

[pb908]

Don't bend anything! Before you do anything else, clean the slow speed movement in zippo lighter fluid properly and then lube the bearings with the finest oil you have. Re dip in the lighter fluid and refit.
I've had these symptoms exactly as you describe on around 7 bodies and cleaning the mech cures it.
It fails upside down because the gears sit in sticky bearings due to gravity. I've just had exactly the same on my 2nd M6 body. Just been cleaned out and relubed. Fixed. Now works upside down, side to side diagonally etc etc.
It's actually quite a good test on an M body and one I do when buying to find out if it needs cleaning inside. Set to 1 sec and fire the camera upside down. The first few frames will probably be ok but as the gears settle in the sticky bearings the slow speeds fail if the camera needs cleaning.

as I said previously, all the gears are clean and running freely, the slow speed escapement assembly move closer/farther as the speed dial turn.
all works as normal as it should be.

even with camera in normal shooting position, if i push the slow speed escapement catch a little bit up, it will not catch the 2nd curtain and problem reproduce again. so it is confirmed, the problem created due to this mechanism.

I don't think I see this UP-DOWN movement on the catch lever of my M2 and M3. I will open another M3 belong to another friend, so I'll give you all an update what is different.

if you can open your m6 and confirm there are no up-down movement of the slow speed catch lever, maybe this is just wear problem on mine, but who know? maybe on yours the lever sticks to down position due to grease 😀, that's why you don't see the problem.

 

[pb908]

My M6 works fine upside-down. If this were a design-fault, the RFF-ers from down under would have noticed it before.
Very impressive technical drawings, by the way

Greetings,

Dirk

just a copy and paste from Leica service manual :angel: and add some color.

 

[nobbylon]

As I said earlier, please don't bend or shim anything. Clean the mechanism properly first. The gears will run when in need of cleaning but will give errors in timings. I checked my m4 and the gap you see looks normal. As for wear, I've never seen any slow speed mech wear, period. Earliest one I took apart was an early M3 which had been a cruise ship camera with probably over 500000 frames shot. Slow speed mech was like new as was the rest of the gear train. Trust me, take it out and clean it.

 

[pb908]

my friend, i just open one m3 for service, and guess what, the 2nd curtain catch claw is very tight in tolerance, no up down movement compare to m6.
I still believe some m6 have design problem, as i see this kind of problem keeps pop out in this forum. Not trying to bash leica anyway. They are man made, nothing perfect.. In this case, m3 outperform m6 in build quality(tight tolerance)