Stuck ratchet wheel screw, Unitas 285

[DanB]

Hi all,

Just started disassembling a Gruen pocket watch with a Unitas 285 movement, Gruen 497. It's very similar to the Unitas 6487 but has a date. The ratchet wheel screw won't unscrew. The movement is clean - no rust to speak of - so I know that can't be the culprit. I have used a lot of force and no progress. I assume this is a regular right-handed screw unlike the crown wheel which is left-handed. Any chance this ratchet wheel screw is left-handed? Any other suggestions will be greatly appreciated - Thanks!

[Nucejoe]

Hi Dan, Proceed with the strip down, remove the train bridge, gears and canon pinion, barrel then comes out attached to it bridge, soak in coca cola for two days, unscrews easy  then.

One advantage of coca cola is it lets total submersion and cheap. How else penetrants may get to arbour and the thread of ratchet screw? 

Do not drop the movement in coke yet.

Regards

[DanB]

Thanks for the suggestion. When I have just the bridge with barrel attached, should I remove the mainspring, or soak with it inside the barrel? If I try to remove the mainspring before the soak, I'm thinking it may be a little tricky to detach it from the arbor, though I'd feel better not soaking the mainspring in coca cola. 

 

[MechanicMike]

Hi Dan-do looks like a nice clean movement. did you try to give it a nudge clockwise to feel any resistance or tightening? don't force it. I've not seen a left handed ratchet screw but you never know.  do you have any kind of penetrant laying around and oilers? maybe some lighter fluid? once you get the bridge with barrel assy. out, I would apply penetrant around the screw head, then turn it over and apply more at the barrel arbor, and a few more dabs to the holes(if any) thru the barrel cap and let it sit. better if over night, checking on it once in awhile. if that doesn't work, I might let it soak in lighter fluid(naptha) for an extended period. overnight is best, checking on it, seeing if it frees up. if all that fails, give the thing a short rinse in iso alcohol to dry it completely. at this point, you might have to add a little heat such as a jewelers lamp if you have one, or a cig lighter. apply the heat SPARINGLY, with the flame about 1/2 to 3/4 inch from the screw, using a circular motion. in other words, don't hold the flame in one place, keep it moving. you don't want to overheat the thing and run the risk of burning fingers. also, make sure your screwdriver width is as close to the width of the screw slot as possible so as not to slip, gouge, scratch or damage the slot or anything else and don't force anything. 

no expert here-just a couple things that have worked for me. try these and get back to us. good luck.

Mike

[DanB]

Hi Mike,

Thanks - I'll give the penetrant a try. I was also thinking of running the bridge and its attached barrel assembly through the ultrasonic using the extra fine watch cleaner and cleaner rinse to see if that loosens it up. I'm thinking this can't hurt, though my one worry is, what if the micro-shaking of the ultrasonic loosens the barrel arbor cap and the mainspring then goes flying?

This stuck screw is such a surprise given the condition of the movement (no corrosion). Could be the last person to work on it just bared down too hard when tightening it.

Dan

[MechanicMike]

27 minutes ago, DanB said:

Hi Mike,

Thanks - I'll give the penetrant a try. I was also thinking of running the bridge and its attached barrel assembly through the ultrasonic using the extra fine watch cleaner and cleaner rinse to see if that loosens it up. I'm thinking this can't hurt, though my one worry is, what if the micro-shaking of the ultrasonic loosens the barrel arbor cap and the mainspring then goes flying?

This stuck screw is such a surprise given the condition of the movement (no corrosion). Could be the last person to work on it just bared down too hard when tightening it.

Dan

hey, 400 lb gorillas are more common than you think! yes, the ultrasonic gig you speak of is fine and might work even better. the chance, I believe, of the assy. trying to escape and go flying, are slim to none. with that cantankerous screw especially. even if it did, you won't lose it. just make sure to watch your eyeballs for flying objects! what size is the movement? also I should let you know that when I use my ultrasonic to clean parts, the solution I use is, yep you guessed it, naptha. parts into screen containers, screen containers into jars with naptha, then parts, containers, naptha and jars into machine filled with demineralized water half full and let er buck. so, I think you're right  on the money. 

[MechanicMike]

Just now, MechanicMike said:

hey, 400 lb gorillas are more common than you think! yes, the ultrasonic gig you speak of is fine and might work even better. the chance, I believe, of the assy. trying to escape and go flying, are slim to none. with that cantankerous screw especially. even if it did, you won't lose it. just make sure to watch your eyeballs for flying objects! what size is the movement? also I should let you know that when I use my ultrasonic to clean parts, the solution I use is, yep you guessed it, naptha. parts into screen containers, screen containers into jars with naptha, then parts, containers, naptha and jars into machine filled with demineralized water half full and let er buck. so, I think you're right  on the money. 

all that being said, we shouldn't forget that this hang-up might not be seized screw at all but something more mechanical in nature such as seized or cross-threaded threads, somehow jammed up mainspring, or the whole dang train is jammed up with broken teeth or broken leafs on a pinion gear or worse. so exercise caution, make periodic checks and close inspections of the things, see if the elusive misfit reveals  itself.  I love beating an "overconfident gremlin." keep us posted...

[DanB]

It's a 16.5 ligne/36.6mm movement. It really is almost identical to the ETA/Unitas 6497 except the motion works are at 12:00 since it's a pocket watch. I didn't think that the ratchet screw could be cross-threaded which would really make it stick if it is, but based on how flush it's lying to the ratchet wheel, that may not be the case. 

The good news is I have a spare parts 6497 movement to call upon in case anything gets really botched up related to the barrel and arbor, so there's not much to lose by trying different techniques. Plus the watch was passed on to me by a friend who knew of my recent interest in this stuff (so nice when that happens) so it's not an heirloom or anything extremely valuable.

Thanks again for weighing in.

Dan

[Nucejoe]

5 hours ago, DanB said:

Thanks for the suggestion. When I have just the bridge with barrel attached, should I remove the mainspring, or soak with it inside the barrel? If I try to remove the mainspring before the soak, I'm thinking it may be a little tricky to detach it from the arbor, though I'd feel better not soaking the mainspring in coca cola. 

 

Two days soak in coca cola wont hurt any metal, the suger in coke, however, may crystalize which is a pain to clean if inside the jewel hole. Personaly exclude hairspring and jewels and soak the rest.

The concern with removing the barrel and mainspring(MS) when still attached to the bridge is MS jumps out violently as you try removing the barrel and leave the arbour and lid still attached and spindle may break. If you plan re-using the MS, you would need to clean it anyway, which if manually I recommend with a brush and not cloth.

[Nucejoe]

5 hours ago, MechanicMike said:

Hi Dan-do looks like a nice clean movement. did you try to give it a nudge clockwise to feel any resistance or tightening? don't force it. I've not seen a left handed ratchet screw but you never know.  do you have any kind of penetrant laying around and oilers? maybe some lighter fluid? once you get the bridge with barrel assy. out, I would apply penetrant around the screw head, then turn it over and apply more at the barrel arbor, and a few more dabs to the holes(if any) thru the barrel cap and let it sit. better if over night, checking on it once in awhile. if that doesn't work, I might let it soak in lighter fluid(naptha) for an extended period. overnight is best, checking on it, seeing if it frees up. if all that fails, give the thing a short rinse in iso alcohol to dry it completely. at this point, you might have to add a little heat such as a jewelers lamp if you have one, or a cig lighter. apply the heat SPARINGLY, with the flame about 1/2 to 3/4 inch from the screw, using a circular motion. in other words, don't hold the flame in one place, keep it moving. you don't want to overheat the thing and run the risk of burning fingers. also, make sure your screwdriver width is as close to the width of the screw slot as possible so as not to slip, gouge, scratch or damage the slot or anything else and don't force anything. 

no expert here-just a couple things that have worked for me. try these and get back to us. good luck.

Mike

No heat specially flame, unless you discard the heated part. I do use heat( soldering gun)  on stuck broken screw thread since I don't collect broken screws.

[clockboy]

Is it a reverse thread.

[KarlvonKoln]

I'm wondering that too.  Physics being what it is, if the crown wheel screw was left-handed, then the ratchet gear screw couldn't be.  But!...if the crown wheel screw was standard, wouldn't the ratchet gear have to be the one to be left-handed? 

[Klassiker]

Ranfft says left-hand thread.

[jdm]

59 minutes ago, KarlvonKoln said:

I'm wondering that too.  Physics being what it is, if the crown wheel screw was left-handed, then the ratchet gear screw couldn't be.  But!...if the crown wheel screw was standard, wouldn't the ratchet gear have to be the one to be left-handed? 

No. The crown wheel screw may be be left threaded because the crown wheel, which turns counter clockwise under it, may tend to undo it. But the ratchet wheel screw does not move related to the ratchet wheel and barrel arbor airbor, no need for it being special, no matter which direction it turns.

That being said, if left threaded  the manufacturer gains commonality of two machining steps, and of two parts if it's identical to the crown wheel screw. To the cost of confusing most repairers as happened here,  and the risk of an unpleasant breakage. At least, both of them should have three slots not one.

[KarlvonKoln]

Thank you for explaining JDM.  That part confused me.

[clockboy]

The movement is a caliber 6500. I still favour it is a reverse thread.

[DanB]

Hi all,

Mystery solved - the ratchet wheel screw is left handed. Wow. I briefly thought that could be the case, but still being new to this (just under a year with the tweezers) I assumed that most if not all crown wheel screws are left handed, ratchet wheels are right. Oh well, lesson learned. I looked for technical info on the movement on the AWCI site but could only find parts info. I should have checked the Ranftt page sooner (thanks Klassiker for that reminder).  

So the screw is out now, no damage done. 

Thanks again to all.

Dan

[Nucejoe]

7 minutes ago, DanB said:

Hi all,

Mystery solved - the ratchet wheel screw is left handed. Wow. I briefly thought that could be the case, but still being new to this (just under a year with the tweezers) I assumed that most if not all crown wheel screws are left handed, ratchet wheels are right. Oh well, lesson learned. I looked for technical info on the movement on the AWCI site but could only find parts info. I should have checked the Ranftt page sooner (thanks Klassiker for that reminder).  

So the screw is out now, no damage done. 

Thanks again to all.

Dan

Good thing you posted this thread,  saved the watch and can drink the coca cola too, don't forget the pop corn.

[MechanicMike]

2 hours ago, DanB said:

Hi all,

Mystery solved - the ratchet wheel screw is left handed. Wow. I briefly thought that could be the case, but still being new to this (just under a year with the tweezers) I assumed that most if not all crown wheel screws are left handed, ratchet wheels are right. Oh well, lesson learned. I looked for technical info on the movement on the AWCI site but could only find parts info. I should have checked the Ranftt page sooner (thanks Klassiker for that reminder).  

So the screw is out now, no damage done. 

Thanks again to all.

Dan

left handed threads for the win! how did you get it? did you nudge the screw clockwise and it began to move? good stuff for future reference. 

Edited August 1, 2020 by MechanicMike
wrong word :)

[DanB]

Yes, I nudged it to the right and it didn't take much for it to loosen. I had applied Marvel penetrating oil to the screw and let it sit overnight so that might have helped. At the outset when I didn't know it was left handed, I did give it a little nudge to the right but it didn't move and I didn't want to make matters worse if I nudged too hard. 

I did buy a can of coke just in case and now I can enjoy it with some popcorn!

[KarlvonKoln]

Now I'm craving Coke and popcorn too.  Interesting tradition here.  Solve a mystery --> have Coke & popcorn.  I'm cool with that.