Longines 6942

[kev]

Hi Gents,

 

I have just replace the mainspring in a Longines 6942. I have also stripped and lubricated the watch. After reassemble the watch doesn't work after winding but if i blow on the mainspring the watch starts and continues to run. Any suggestions would be gratefully received.

I should add that i have been told the watch hasn't worked at all in years.

[HSL]

42 minutes ago, kev said:

I have just replace the mainspring in a Longines 6942. I have also stripped and lubricated the watch. After reassemble the watch doesn't work after winding but if i blow on the mainspring the watch starts and continues to run. Any suggestions would be gratefully received.

You must mean if you gently blow on the hairspring it jumps into life or?
There usually are two reasons for this behavior.
1. You still have some dirt in the pivot holes.
2. The lubrication on the balance jewels are to rich.

If you by accident lubricated the pallet fork it should just run for a while and then stop.
So you should just remove the end caps on the balance jewels, use a very sharp peg wood to clean the pivot holes or just dip them into a one dip solution and shake. 
Put a small drop of 9010 on the flat side of the end caps and reassemble.The dot of oil should just cover around 30 -40 percent of the end caps area. Put the jewels back into place.
Remove the pallet fork, clean the pivot hole on the plate, push both sides of the pallet fork into Rodico so it will be clean, clean the fork bridge pallet hole. Put all back and don´t lubricate the jewels.
Put the balance bridge into place and of they should go..

If you still struggle just howl again and I might put this Russian movement away and make a small PDF guide.

[kev]

Hi HSL thanks for the help. Unfortunately I have stripped, Cleaned and reassembled as you described but I still have the same problem. Each time the watch is stopped for setting it will not restart unless I blow on the hairspring. Then everything appears to work fine.

[HSL]

That doesn't sound very good, this movement has the second stop function, if you pull out the winding stem it ticks until the second hand is in zero position. This is a quite handy function while setting the watch but might introduce some weird faults.

But as a fault finding exercise we could start here.

Begin with  releasing all power from the mainspring, you do this by lifting the click.
Pull the stem out and remove the balance bridge.
Remove the pallet cock and pallet fork.
Put the stem back in and put it in setting position. Now turn one or two times on the winding stem. Nothing should happen at this stage.
Push the stem into winding position, now you should have a release of power, the train wheels and escape wheel should rotate free.
Look at the escape wheel it should run free slightly longer than the train wheels. If not there is to much oil. Clean it off with Rodico.
When faultfinding you could clean out the oil from the escape since it just going to run for a short while. The oil already stuck on the pivot pin should be enough.

If everything runs great here we have a problem either in the pallet fork area or the balance area.
Sometimes the juvels are slightly different you could always try to switch them after you checked the drive train.
I will setup a test station trying to replicate the error but that might take a while. I got three volunteers.

 

[HSL]

Just finished a quite extensive session with these beauties to try replicate the fault you mention.
Nothing except total loss off power by heavy dirt in the drive train would make it stop the balance from oscillating by it self. I used a small drop of maple syrup to simulate an old oil. So we can rule the drive train out.

I didn't find any worn balance pivots in my goodie bag just some broken ones so that test is unfortunately excluded and you just have to check the end shake and side shake with a couple of tweezers.

Here comes a small checklist from the tests.

Too much oil on the escape teeth made it hard to get oscillate by it self.

Dirt on either entry or exit pallet made it hard to get oscillate by it self.

Too much oil in the escape wheel pivot made it hard to get oscillate by it self.

Oil accidentally applied on  the pallet fork pivots made it hard to get oscillate by it self and later went into a halt.

Dry balance jewels made it occasionally  hard to get oscillate by it self.

Broken pivot jewel in the balance made it hard to get oscillate by it self and go to a stop when turned around.

Dirt in the impulse pin made it hard to get oscillate by it self.

Broken pivot on balance staff lower part made it hard to get oscillate by it self, stopped when turned around. 

A slight bend upwards on the pallet fork made it hard to get oscillate by it self.

Beat error lever accidentally moved out of position  made it hard to get oscillate by it self.

A magnetized  hairspring made it hard to get oscillate by it self.

To speed up this small investigation I had to add one more movement into the process it got to be the lucky one with magnetized hairspring.

So if you have cleaned the movement correctly and checked the items in the list I can't se any other reasons for the balance not to swing like on the one in the attached video.

[kev]

HSL, thank you for all of your help with this problem I really appreciate it. It would appear that the cause of the problem was a slight bend in the escape wheel top pivot. Everything now seems to be working fine. Success at last! 

I'm sorry it took so long to respond but I have ben away.