Bunn Special erratic Face Down

piedmontg

Registered User
Jun 14, 2009
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Hi

I just acquired (from my mailbox) a Bunn Special, 161A, Type 2P. Whenever I get a watch through the mail I take to the bench open the back and try and observe if anything looks wrong under a microscope, ie jewels cracked, pallet stones OK, anything I can see. Next I start to wind and see if it will take off on its own. Assuming all goes well I put it on my timing machine weishi 1900 and check in positions.

This watch would not start face down. The watch tried to start, that is it would erratically move the escape wheel and pallets. The balance wheel would go erratically. Then I moved it slightly and it took off. Moved it around some more and stopped. When I say move it around, the watch is face down and I just tipped it a bit ie 5 degrees or so. Sometimes I could hold in a position and it would run. Flat face down it ran most of the time. If I elevated the stem about 5 degrees it would become erratic and finally just stop.

I put the cover back on and set it down face up, looking at the seconds hand, there was no hesitation it ran along. Did that in all other positions and it ran along just fine, face down - tilted a bit stops.

I put it on the timing machine (I tried getting everything under the headings, it is fine on the edit screen but smashes it all together when it publishes it):

Position S/D Amplitude B.E

FU -3 to -5 242 to 247 .7

SU -19 to -22 227 to 230 .9

SL -18 to -23 226 to 229 1.0

SD -1 to +3 221 to 224 .8

SR -4 to -7 228 to 234 .5

FD erratic and stops

Wish I knew how to better read the display on the 1900. I assume the two lines are triggered by the entry and exit pallet motion against the escape wheel. On some of my watches, that run very well, those two lines consist of a set of dots that are very concise in their order, one right after another, no jiggle ie one dot higher than the next just marching right along. On this watch the top line has “jiggle” dots not right in line, all over the place even below the bottom line. The bottom line close to consistent but a small ”jiggle”. See photos. In FU 1 the beat error changed and the display shows erratic upper line, in FU 2 about 2 minutes later the beat error changed again and the top line “calmed down” a bit. In FU 3 a bit later the top line has points below the bottom line. SU 1 both lines have dots above the main lines – beat error moved around.

In reading repair posts and books there is an emphasis on diagnosing before tearing it down. I have looked at everything I can see with cover off. As best I can determine there are no cracked jewels, the pallet jewels look OK from this view, no obvious cracks or chips. I cannot see the roller jewel.

I know I am asking the impossible- well maybe- but what else could I try and observe without disassembly.

Thank You

Bob


Bunn-Sp-161a-2p-v-2.jpg



FU 1
FU-1.jpg


FU 2 - about 2 minutes later

FU-2.jpg
FU 3 a bit later


SU-1.jpg

SU 1

SU-2.jpg
 

Skutt50

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Mar 14, 2008
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Actually you can't check all jewels with the dial still in place.

Also it is fine to check the performance of the movement before disassembly, if nothing else for after service comparison.

The "jiggle" can be as simple as some dirt on a pallet jewel and the stoppage can also be linked to old oil in some part of the escapement..

I am sorry to say it but before drawing any conclusions you need to take it apart, clean, assemble and oil. Only then can you start proper fault finding.......
 

karlmansson

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Apr 20, 2013
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Skutt is right, this can be due to any number of factors. Although one that can be pretty easy to check is if the dial is loose. In the dial down position, this can cause it to fall down slightly and interfere with the seconds hand.

Other places to look for something that varies between dial up and dial down are things that are affected by end shake. So position of the hairspring on the balance staff, excessive end shake in the balance causing either the balance wheel or the spring to touch the center wheel or come out of alignment with parts of the fork lever. Or the fork lever dropping out of contact with the escape wheel. A cracked dial side balance cap jewel could also lead to this and is something you can't see from the back of the movement.

The lines on your timegrapher are the impulses, in either direction. Blue is tick, yellow is tock. To be able to see the separate sounds of the escapement and variations in the interaction between pallet stones and EW you need to be able to see the wave form of the sound. Each dot on your display is in reality about five sounds where three of them can be useful for diagnosing errors. Having two colours like that looks handy! I only have the monochrome display on mine.

Best of luck!

Karl
 

piedmontg

Registered User
Jun 14, 2009
37
22
8
Thank you for some direction. I need to decide what to do. As I just purchased it i may take a return approach. I would not like to take it apart and find I am not capable of fixing it, then I would not be able to return it.

Also I appreciate the insight on reading my timer "dots". I have some software from Watchuseek forum that shows wave forms, another thing I need to learn how to read.

Bob
 

meatlips01

NAWCC Member
Mar 17, 2021
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I'm wondering if you got this watch from the same seller I got my bunn special movements from. So far I've also encountered problems, but at least seeing those cleanish lines on your timegrapher tells me that at the very least the issues with this particular movement are solvable. I also believe that Skutt is very much correct here. You need to break this guy down and give it a good once over and maybe a good cleaning.

I got a bunn special 60 hour and the cap jewel on the foot was cracked. Even after a cleaning I can't get anything even remotely looking like your timegrapher images. Mine can't even tell how fast the balance is running. I get the equivalent of snow and the timegrapher keeps trying to figure out the actual speed. I'm beginning to suspect that the hairspring is not original to this balance since the balance serial matches the movement. I kind of wish I had a proper hairspring vibrating tool just to see if it's even the right length.
 

Skutt50

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Mar 14, 2008
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I kind of wish I had a proper hairspring vibrating tool just to see if it's even the right length.
You can check this yourself. Support the hairspring over a watch with a seconds hand. Let the balance hang down like a cone and rest the lower balance pivot on the crystal of the watch. Then give it a puff and start counting the vibrations during one minute (watching the seconds hand). If I remember correctly there should be 150 oscillations during one minute for a 1800bph movement.
 

piedmontg

Registered User
Jun 14, 2009
37
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I decided that since the seller offered to take it back, I would just do that. As soon as I touched it ie took it apart I could not return it no matter what I found. It was a lot of money, at least to me, and I am opting to keep looking.

I appreciate the insights. When I get more repair mileage under my belt so to speak I might give something like the above a try.

Bob
 

meatlips01

NAWCC Member
Mar 17, 2021
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You can check this yourself. Support the hairspring over a watch with a seconds hand. Let the balance hang down like a cone and rest the lower balance pivot on the crystal of the watch. Then give it a puff and start counting the vibrations during one minute (watching the seconds hand). If I remember correctly there should be 150 oscillations during one minute for a 1800bph movement.
After some online research I think the likeliest culprit is the balance is out of poise. Close examination of the staff shows that whoever replaced this thing managed to shave part of the pivot cone down when they reinstalled the double roller. I have a replacement staff on the way. Then I'm going to put this guy on my poising tool and get it perfectly poised. Hopefully that will solve my issue.

I'm still on the hunt for a replacement cap jewel for the foot since it was cracked.
 

karlmansson

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Apr 20, 2013
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After some online research I think the likeliest culprit is the balance is out of poise. Close examination of the staff shows that whoever replaced this thing managed to shave part of the pivot cone down when they reinstalled the double roller. I have a replacement staff on the way. Then I'm going to put this guy on my poising tool and get it perfectly poised. Hopefully that will solve my issue.

I'm still on the hunt for a replacement cap jewel for the foot since it was cracked.
Are you referring back to your previous post or the OPs situation? I recommend starting your own thread for you watch, providing info on a separate watch will only get confusing here.

The balance being out of poise will not cause the issues the OP had with his watch. Poise has very little effect on differences between DU and DD.

Regards
Karl
 

gmorse

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Jan 7, 2011
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Hi meatlips01,
Then I'm going to put this guy on my poising tool and get it perfectly poised. Hopefully that will solve my issue.
If you go through that process, which involves testing the poise of a motionless balance without its balance spring, you'll then put the spring back on it and discover whether static poising has any influence on the dynamic performance or the difference between DU and DD.

Regards,

Graham
 
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John Runciman

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Are you referring back to your previous post or the OPs situation? I recommend starting your own thread for you watch, providing info on a separate watch will only get confusing here.

The balance being out of poise will not cause the issues the OP had with his watch. Poise has very little effect on differences between DU and DD.
one of the things that makes for a really confusing reading is when people hijack conversations or discussions. Each watch is unique each watch deserves its own discussion while it may seem like your problem is the same as what ever started a discussion it may or may not be an each watch is unique

Thank you for some direction. I need to decide what to do. As I just purchased it i may take a return approach. I would not like to take it apart and find I am not capable of fixing it, then I would not be able to return it.
out of curiosity was the watch sold as running condition serviced etc.? Then yes playing with a watch when you have a warranty whether it's a warranty from a new purchase or a repair warranty is always a bad idea if there's a problem send it back. Especially if it was sold as running and not



I got a bunn special 60 hour and the cap jewel on the foot was cracked. Even after a cleaning I can't get anything even remotely looking like your timegrapher images. Mine can't even tell how fast the balance is running. I get the equivalent of snow and the timegrapher keeps trying to figure out the actual speed. I'm beginning to suspect that the hairspring is not original to this balance since the balance serial matches the movement. I kind of wish I had a proper hairspring vibrating tool just to see if it's even the right length.
The balance being out of poise will not cause the issues the OP had with his watch. Poise has very little effect on differences between DU and DD.
After some online research I think the likeliest culprit is the balance is out of poise. Close examination of the staff shows that whoever replaced this thing managed to shave part of the pivot cone down when they reinstalled the double roller. I have a replacement staff on the way. Then I'm going to put this guy on my poising tool and get it perfectly poised. Hopefully that will solve my issue.

I'm still on the hunt for a replacement cap jewel for the foot since it was cracked.
notice I quoted a lot of things because I'm trying to figure out what's going on in the see if I can help you as I want a clear picture. First off timing machine if it's showing you snow is telling you it's having a problem. If it's displaying numbers and you cannot see lines clear lines the numbers are total crap.. Simplistically garbage in garbage out and you cannot use the numbers for diagnostics. Someday the timing machines will artificial intelligence be smarter than us and it will ask he display them on the screen that you have to fix the watch better before it can tell you anything.

visually how does the watch look like it's running? When you look at the balance wheel how was the hairspring look? As a whole variety of things that can cause snow in the timing machine to get to the bottom of that requires observation on your part. Even more important requires that you understand what you're looking at. Also not just what you're looking at listen to the watch how does it sound. Like for instance of the hairspring is bumping into things like the center wheel it usually makes a clanging sound. It is rubbing on the balance arms it doesn't always make a sound it can but it's not as obvious as when it bumps into something.

as you getting total snow on the machine there other things out cause minor snow but almost pointless to discuss those until you can get a better signal. Which means you have to do in the visual assessment of the balance wheel and listen to the watch and maybe get us some pictures like looking down at the balance wheel pictures of the pivots is always hard to diagnose remotely from a description.
 

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