Record 1955-2 train question

[StuartBaker104]

I bought an old Record cal 1955-2 recently on eBay. It was described as needing a new balance, but otherwise looked in great condition for what must be nearly 50 years old.

Indeed it needed a new balance, although at first I was confused. The hairspring wasn’t located between the pins so I sorted that and put it on the timegrapher whereupon it ran beautifully... although I subsequently realised when it lost time that it was running at 18000bph instead of 19800bph. I tracked down a new balance and now it beats beautifully at 19800bph... but it still loses 5 seconds every minute.

The 1955-2 is equivalent to Longines 505 (http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&&2uswk&Longines_505). Longines 506 and 508 in the same series run at 21600bph, so I’m assuming that someone took parts from a 506 or 508 train and put them in this watch. Question is, how do I find out which ones? The usual on line parts source directories (Cousins, Boley, Borel) don’t list the train wheels for the two so I can’t work out which ones it might be.

I have seen escape wheels for both the 19800 and 21600 calibres listed on eBay and the photos of these show identical numbers of teeth, so I guess that isn’t it, (unless one of them is wrongly listed) but I wondered if anyone knows any simple tricks for working this out?

[Gpsluvr]

It sounds like the hairspring needs to be shorter. Too long and it will run slow, too short and it will run fast. This is provided that it simply isn’t running erratically because of another problem somewhere.steve


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[JohnR725]

There is a formula for calculating out the frequency so you have the right gear ratio for your gear train. It's found that the link below. You can at least do the calculation and see what frequency your gear train thinks it's for. Then if you're good at math you can probably figure out which wheel is at fault. Then the escape wheel for the 506 and 508 are the same. The number of teeth on the escape wheel are probably the same but the number of leaves On the pinion is probably not. 

https://books.google.com/books?id=nZ27BvJwol4C&pg=PA81&lpg=PA81&dq=Calculation+of+the+number+of+vibrations+per+hour+Watch&source=bl&ots=5qP-k1sz-I&sig=bL28H-7jfrQKM6V4-l8B88Quo7I&hl=en&sa=X&ved=2ahUKEwiH1oGglYXeAhW0KX0KHc05BWsQ6AEwCXoECAAQAQ#v=onepage&q=Calculation of the number of vibrations per hour Watch&f=false

[StuartBaker104]

Thanks John.

This was easier than I thought when I got into it...

(72 teeth on 4th wheel x 15 on escape wheel x 2 pallets x 60 rotations of second hand per hour) / 6 leaves on escape pinion = 21600 bph

Changing the leaves or teeth on the escape wheel gives wierd answers, but substituting 66 teeth on the 4th wheel gives 19800bph. Lo and behold, looking at pictures on eBay, the correct listed part has 66 teeth. It even has 7 spokes instead of 6 to make it easier to tell apart.

So far my £45 bargain watch has cost me £40 to get a balance sent from the US (which I was kind of expecting) and now it looks like another £25 for a 4th wheel, and I still have a worn bush on the auto winder and a dodgy quick date change to sort out before I strip it down for a proper clean. Let’s hope I don’t find much else, and it’s a good job I’m not doing this (or worse still paying someone else) to make a profit!

 

[Tmuir]

Nice detective work, I can see why you bought it though as I really like the simple uncluttered look of the dial