7751 Moonphase - Chronograph Use Slows Watch

[Folkvisor]

Hi

I was wondering if anyone has some experience with a chronograph slowing a watch considerably - 15 minutes/hour when the chronograph is engaged. 

I'm wondering if the pinion is putting too much pressure on the chronograph seconds wheel.

The watch keeps excellent time otherwise: +/- 2seconds/day on average.

I look forward to your ideas...anything but spraying the movement with WD40 is welcome. ;-)

Dave

[HSL]

In Sweden we have something called 5-56 spray lube that is what it takes! 
I have had the similar symptom with a different complication but stillbuilt on the 7750, in that case it went away when I put a new mainspring in.
Otherwise I haven't experienced it.

[Folkvisor]

Thank you for your contribution.

Since the movement is new I don't think it should need a new mainspring but one never knows about anything these days.

Jag har släckningar i Vänersborg, Alingsås och Värgon, också i Stockholm; där man säger 'sk' fel enligt mina släktingar i Vänersborg...

MVH

[HSL]

A new one .. that's no good.

I have a note where I written ETA 7751 -> Longines L678.2 -> Omega 1151 maybe one can find a similar problems there.
Jag bor i småland så där uttalar man inte bara 'sk' fel..
 

[Folkvisor]

Well, I found out that it doesn't lose time for the first hour but, in the second hour, it lost almost 10 minutes with the chronograph running for 30 minutes past the first hour - total 1.5 hours. I have no idea...

Bratteborgsgård är i Småland.

[HSL]

One hour without loosing time. Then to be sure it's not the mainspring you actually could wind it up every half an hour, doing that should give the drivetrain the same power all the time, if it's okay then the fault might be in the mainspring, lack of lubrication in the barrel, lack of lubrication of the arbor or even worn seats, but since it was new movement the last is not an option.
Otherwise we have to move on to the drivetrain, and later on dissengage the complication and run it without it.
A systematic approach is a must I think.

[Folkvisor]

Thank you, again for your ideas.

I'm not sure why it should be necessary but it might be a good idea to clean the chronograph portion of the watch. But, that's a huge job and who knows if it would really help...

And why would there be a problem with the chronograph movement when the rest of the watch works flawlessly? And why after the first hour of running the chronograph? 

It's all very strange. I'm at a loss...

 

[nickelsilver]

It could be the depthing of the rocking pinion to the chronograph runner is too deep

It could be the tension spring for the chronograph runner was installed incorrectly or is damaged and greating too much drag

It could be the chronograph runner pivot (long one for the hand) is bent and causing the hand tube to rub

It could be that the hand tube is damaged and rubbing

It could be that the rotor screw is not the correct one, and the screw in place is touching the upper pivot of the chronograph runner

 

The last one is the easiest to check, and the screw should have a bit of a "divot" in its end.

 

It could be something else (just dirt somewhere for example). That it runs OK for a bit from full wind probably just means that it manages to go with that extra bit of kick the end of the mainspring gives. If you have a timing machine it would be interesting to know the amplitude with chrono off and chrono on, at full wind.

Edited April 8, 2020 by nickelsilver

[HSL]

Well cleaning the complication is the last thing to do as you see on the list while troubleshooting, but just as you say the rest of the watch seems to work OK so you have to look at the parts moving slowly, like the mainspring barrel, it has a relativly large slow moving gear so there for the mainspring could be a culpitt, then one have to look at the drivetrain like the hour wheel, and if that is OK you only have slowmoving gears in your complication. If the rest like the escapement is running like the orient express there is no sens to look at that.
Intermitent errors are the hardest to find but the most rewarding.

[Folkvisor]

Thank you both for the advice. I will certainly use the check list and see what I can do about the timing machine read-outs.

I am, obviously, an amateur so I'm not in a big rush to dismantle the movement. 

It would be most rewarding if I could find the problem and fix it.

 

[Folkvisor]

What I find strange is that it works fine for an hour or so before the problem cuts in.

Intermittent problems are fun to find on pianos too...