Tissot problem

[chrisdt]

Hi Guys

Can anyone give some ideas on what may cause the problem with my Tissot 782-1 movement?

The problem is this. The movements power reserve is 36 -40 hours. Fully wind, set the time and it keeps excellent time for around 15 hours. The next 15 hours or so it gains time at a regular rate of about 12 minutes per hour. Wind it, set the time and the watch keeps time for 15 hours or so then gains time as above. I can understand perhaps losing time as the mainspring loses power but not gaining time. Any suggestions would be helpful. Thanks 

 

[JohnHutchins]

Is this a possible explanation?

A fully wound watch generates maximum torque through the gear train and pallet fork against the impulse jewel causing the balance wheel to swing with maximum amplitude. 

    However, as the mainspring winds down the torque may be decreasing, so there is less energy applied to the impulse jewel which creates a smaller amplitude. A lower amplitude means the balance wheel swings in a shorter arc so the hairspring is oscillating faster producing a faster rate. 

 

Edited August 28, 2019 by JohnHutchins

[AndyHull]

I suspect this is part of the story. The fact that it lasts 15 hours suggests that the mainspring may be the issue, as it reaches a certain point of its expansion within the barrel, it may be catching (possibly on some dirt, or possibly on a wear mark within the barrel or barrel lid), once it sticks in this way, it then has far less torque, and acts as described in the previous post.

I would start by cleaning and inspecting the mainspring.

[anilv]

Has this watch been cleaned and serviced? If not then it should be and a new mainspring included.

Anilv

[jdm]

3 hours ago, anilv said:

Has this watch been cleaned and serviced? If not then it should be and a new mainspring included.

Correct, and as with any timekeeping issue a timegrapher picture should always be included. You may see pattern or amplitude screaming: service now. 

[Nucejoe]

Hi chris, How sure are you of the hairspring? May remain "sticking"  longer at low amplitude? 

Applying  plenty of kerosene or diesel fuel to escape teeth and pallets and fork pivots, will certainly increase the amplitude drastically, gives you a chance to check timekeeping passed 15 hrs. 

No doubt you will check the barrel, unlevel lid, overstreched/overstraigthened HS, arbor endshake.....

Regards joe