Omega 620 troubleshooting help

[rubberteeth]

Hello esteemed members

I recently acquired tiny 22mm omega with 620 movement, non runner. Balance did not move. First I thought oh how easy there's a case clamp screw lodged somewhere in gears as one clamp was running around the insides without screw. As it turned out this wasn't the case as screw was not present at all and mainspring end was broken. 

So after installing new mainspring, cleaning and oiling this problem still persists. Balance swings freely when pallet fork is not present.  Pivots are not bent or broken. Roller is in correct position when balace not moving. I noticed there seems to be a very tiny gap between roller table and balance wheel itself but that's likely just how it should sit on staff. Hairspring good. Train on it's own is also moving freely. All the gears are in perfect condition, no broken teeth or pivots. When I offer pallet fork to the movement and manually move it, it's engaging with escape wheel as it should although there's no fast "snap" of the escape. I don't know how to say this properly but it seems to me the action is slower as it should be(might be nothing). Pivots on fork are also in pristine condition just as balace ones. When fully assembled balance wont move on its own, it can be somewhat persuaded with air blower from one side to another but comes to abrupt halt almost immediately. Movement is demagnetized, it wont run in any position dial up down or side. Worst about this is 620 movement is so small I have a problem looking at balance and pallet fork engagement (or non engagement to be honest). 

I've seen some cheap donor movements on ebay but I'm reluctant to go that way for now.

What course of action would you recommend? Any opinion would be appreciated 

 

[nickelsilver]

I would check the fork freedom with no escape wheel present. A very light puff of air should move it from banking to banking.

 

Then I would install the balance, and see how it acts with the fork. That the roller table is not against the hub is troubling- it should be firmly against it. I think this is likely the issue. The roller jewel could be touching the guard pin, or the table itself touching the horns, or both.

[Nucejoe]

 Furthur to the above, I would check shakes on fork arbour. 

The fork should fall by its own weight, and fork pivots- jewels un-lubed. 

Fork must snap STRONGLY  from side to side, with a few turn of crown turn.

Rgds

[rubberteeth]

16 hours ago, nickelsilver said:

I would check the fork freedom with no escape wheel present. A very light puff of air should move it from banking to banking.

 

Then I would install the balance, and see how it acts with the fork. That the roller table is not against the hub is troubling- it should be firmly against it. I think this is likely the issue. The roller jewel could be touching the guard pin, or the table itself touching the horns, or both.

I checked without escape and fork was not moving. I could squeeze the life out of air blower and no movement happened. No endshake was present so decided to adjust baseplate jewel slightly(0,02-0,03mm) and check the result. When I put fork back, other jewel on bridge popped out (like stayed on pallet fork pivot visibly loose), bridge not even screwed down, just with slightest pressure from tweezers. First time this happened to me   

Regarding the gap between roller table and balance wheel. When I look at staffs for this movement online there's different diameter on staff for wheel and roller so it might be as flush as possible sitting on that flat shoulder to biggest diameter . It's really small and almost unnoticeable. Less than human hair. 

[nickelsilver]

Ah I mis-read, I thought there was a gap between the roller and the hub; the hub is in between the roller and balance and it's normal to have a gap there, sometimes tiny, sometimes large, depending on the size of the hub.

 

Try pushing the jewel back in, until it holds, and if there is no shake, try pushing the jewel in the mainplate down.

[rubberteeth]

7 minutes ago, nickelsilver said:

Ah I mis-read, I thought there was a gap between the roller and the hub

If there is any gap between those two I wont be able to tell even under my budget microscope. 

11 minutes ago, nickelsilver said:

Try pushing the jewel back in, until it holds, and if there is no shake, try pushing the jewel in the mainplate down.

no more spare time today and it honestly stressed me out quite a lot. I'll sleep on this, try refitting it tomorrow and just pray this fork endshake is the main issue why it wont run, fiddling with balance and roller is the last thing I wish to do 

[rubberteeth]

Fork issue is fixed I believe but case is sadly not solved yet. Refitted the jewel, adjusted height a bit and it snaps smoothly as it should. Light puff of air moves it form banking to banking. There's also some minor improvement with balance. It can move more freely now but still wont oscillate as it should. At most it moves fork twice and then it's more of a banging on it on one side. 

Checked the gap again, roller it fitted flush with angled part. gap I saw before is the angled part of the staff in between wheel and roller.