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Khan

As 1802/03 too slow despite serviced

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Hi

It ran many seconds slow per minute, even though my app time measurer told it was running absolutely fine. Now after full cleaning and lubrication, it seems better in amplitude but same time loss, but stops after half minute run. I also checked the balance with another spare part, so it can't be magnetisation, hairspring looks fine. Visually, the escapement wheel freezes and the rest stops immediately. It's a mystery for me this time: Is it a loose off center canon pinion?? 

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1- Sounds like bad teeth on escape wheel,

2- pallets have moved in the forks groove or misalliegned.

I presume the impulse is in beat. Dose it run for longer than one turn of escape wheel? You may mark the escape with magic marker and see if it stops at the same position of escape wheel. 

Remove the cock, the fork should get close to the banks as you give it a nudge but not hit them. 

Are you familiar with overbanking fault?

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I might have a spare for escape wheel. Notice that prior to cleaning, it was running on a long power reserve but with terribly time loss. Like 2 hours per day.

Yes, it runs more than a turn in the escape wheel, maybe half minute. Please introduce me to overbanking fault, thanks in advance. 

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Firstly, there is a massive fibre sticking out through the main plate from under the barrel. If it ran prior to cleaning, and nothing was broken or dislodged as part of the cleaning and reassembly process, but now it keeps stopping, the primary suspect is foreign particles in the works. It only takes a single small fibre in the wrong place and the movement will stop so I would suggest another strip down and inspect to make sure that it is absolutely clean, and then reassemble taking care that no more fibres get into the works.

Hopefully this will at least get the watch running again.

You mentioned "many seconds slow per minute" but the timing app on the phone showed that it was ok. Assuming that the timing app works properly (you can test this using another watch of known accuracy) then the usual cause for this is a loose canon pinion which results in the hands moving slowly, erratically, or not at all, even though the movement is running fine. You can verify this quite easily by ignoring the hour and minute hands and timing the seconds hand against a known reference. This is because the loose canon pinion issue only affects the hour and minute hands, and not the seconds hand. If the seconds hand is making 1 full revolution per minute then it confirms the results of the timing app on you phone, and the canon pinion is slipping. You can even double check this diagnosis by assessing the resistance at the crown when setting the hands; again, little or no resistance means loose canon pinion.

If the seconds hand is indeed taking significantly more than 1 minute to make a full revolution then the movement is running slow. If it is 5 seconds slow per minute then that equates to 7200 seconds per day which is way beyond the adjustment range of the regulator and suggests that someone has messed about with the balance assembly or the train wheels.

If the problem is with the balance assembly then possible causes are;

1. Someone has fitted too long a hairspring.

2. If it is a screwed balance then someone has added extra weight to it.

3. Possibly insufficient end shake on the balance staff resulting in a lower angular velocity for the balance although this would also be associated with reduced amplitude which could compensate for the slower balance velocity, and is more likely to stop the thing altogether.

I can't think of anything else that would cause the period of the balance to increase, just about everything else decreases the period resulting in the watch running fast.

If the problem is with the going train then it would suggest that someone has swapped out one of the wheels with a wheel from a movement that is designed for a balance wheel assembly that oscillates at a higher frequency than yours. This would indeed show the correct rate on the timing app, but the seconds hand taking longer than 1 minute per revolution.

First step though is to re-clean the movement and get it running, then check the canon pinion.

 

ps. As has been mentioned many times before, if the amplitude is very low then the timegrapher or timing apps can show complete rubbish data, so visually check that the balance wheel has decent amplitude before evaluating the data from the timing app.

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Good eyes marc. Taking a closer look now, the barrel lid too, appears sitting uneven, it may rub on mainplate and virtually bring the movement to a hault.

If uneven, remove the barrel, push on the lid to snap in evenly. 

Suppliment power by pushing on BARREL GEAR with wood, see if it picks up running.

 

 

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Thanks to both of you for enriching knowledge sharing. Very grateful for your effort.

I just took cleaned and assembled the movement again. It still doesn't keep time. It looses 20 seconds per minute. The good news is that it's now running. I also tightened the off set canon pinion slightly and turning hands now seems with the correct resistance. When taking apart the movement, I realized the pivot of center wheel on dial side was tilting. I straightened it as good as possible and now it's 'dancing' within its outer width when you look from side. (Hope it's good enough). I believe that could be the reason for movement in stopping. I have maybe taken the escape wheel from as 1950/51, if any spare part from a family movement, which has higher beat. The balance is original. 

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5 hours ago, Khan said:

I have maybe taken the escape wheel from as 1950/51

That could be the problem.

The 1950/51 beats at 21600BPH and the 1802/03 beats at 18000BPH. The escape wheels are not likely to be interchangeable.

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Hi Marc

Thanks for letting me know. Are there any parts that can be interchangeable in such case? And what makes a watch beating at higher rate designwise? 

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Some parts are interchangeable between calibres in the same model family and some aren't. The Jules Borel web site has a very useful facility for working out what parts will fit what movements. http://cgi.julesborel.com/

The beat rate of a movement is determined by the balance assembly and is primarily a function of the inertia of the balance wheel (determined by the size and mass of the wheel) and the length and strength of the hair spring. It is a specific design feature of any given movement.

So I happen to have an 1803 and a 1950 in my to do box at the moment, so with a spare half hour this evening I did some tooth counting.....

With both of these movements the center seconds wheel drives directly off the escape wheel pinion.

On the 1803 the the Center seconds wheel has 80 teeth and the escape wheel pinion has 8 leaves, so the escape wheel rotates at 10rpm. The escape wheel has 15 teeth, so that's 150 teeth passing through the pallet per minute, which is 2.5 teeth per second. It takes 2 beats of the balance to get 1 tooth through the pallets, so that's 5 beats per second, or 18000 BPH.

On the 1950 the Center seconds wheel has 72 teeth and the escape wheel pinion has 6 leaves, so the escape wheel rotates at 12rpm. The escape wheel has 15 teeth, so that's 180 teeth passing through the pallet per minute, which is 3 teeth per second, so that's 6 beats of the balance per second, or 21600 BPH.

If you use a 1950 escape wheel in an 1803 without changing anything else then you have the escape wheel turning at 10rpm (determined by the beat rate of the balance) but only 6 leaves instead of 8 leaves on the escape wheel pinion. This means that in 1 minute the escape wheel turns 10 revolutions, or 60 leaves leaves worth of engagement with the center seconds wheel, which has 80 teeth, so the seconds wheel will only make 0.75 of a full rotation. You need another 20 leaves worth of escape wheel pinion rotation to get one full rotation of the seconds wheel, which takes an additional 20 seconds. So with this combination it will take 1 minute 20 seconds for the seconds hand to make 1 revolution of the dial when the balance wheel rate is correct (18000BPH).

 

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That couldn't be more explanative and informative. I'm amazed of the effort done in the research. My order record says I have replaced the escape wheel from a 1950. Therefore, I just ordered a spare 1803 movement to make it right. Thanks again, much appreciated. 

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