Here we go again......cheap becomes expensive very quickly.

[ftwizard]

Bought another "cheap" watch off eBay, an Oris, with a 702 movement. Well the mainspring has broken and it doesn't seem to be available from Cousins. Does anyone have one, or know where I can get one, or even what alternative would fit?

[ftwizard]

Okay, so I've found a couple in the Cousins catalogue, close, but not exact. Does anyone know what is the most critical measurement. The depth? the thickness? the length? or the barrel size?

Also, how do I know what bridle it will come with? it's a bit vague in the catalogue.

[clockboy]

All you can do is get a near as you can to strength & length. The height is important it must not be to high because it could rub on the barrel. 

In my "Generale Resorts" catalogue there is no Oris 702.
It has the following :
692,695,698.  Spring No. GR 3730-1or  712,715,718 Spring No. GR 3741-1. The height of these is 1.40mm

 

[JohnR725]

Where are you measuring the depth in the mainspring? Then it would help if you gave us dimensions something for us to look for?

Normally mainsprings are measured by The width or as cousins calls it height. Then the Thickness (Strength) Followed by the length. The barrel size is only important if you're hoping to just push the spring in out of the package.

[ftwizard]

According to Ranfitt, there is a 701,702,704 & 705. Dimensions should be 1.65 x 0.095 x 270 x 8

I've found a GR4475 or GR47311 which are close. I wonder which is better, thicker or taller, Hmmmm.....

Edited September 10, 2016 by ftwizard

[JohnR725]

Do the dimensions you have come from a website or did you measure the spring? The reason why ask I always like to measure the spring in the watch before looking for another spring. Providing somebody hasn't put it inappropriate spring in at least you know what you're starting with versus what you find listed somewhere else. . Then "Ranfitt, there is a 701,702,704 & 705" Do they all use the same size mainspring? The reason I'm asking is I found the suggestion for the 705 to be this 1.60-.09-260 8  4463-GR

 

 

[clockboy]

I would measure the existing Spring


Sent from my iPhone using Tapatalk

[ftwizard]

I did measure the spring, and it was there or thereabouts as suggested by Ranfitt. The GR4463 seems like a good replacement as well.

I'll have another measure and see which one is closest to the original.

I have found a spare that fits reasonably well, so I'll try that first, see how the watch runs, then if it's worth it, I'll get one of the suggested springs.

Edited September 10, 2016 by ftwizard

[StuartBaker104]

You can also use David Boettcher's calculator here: http://www.vintagewatchstraps.com/blogmainsprings.php

The height of the spring should be about 0.2 mm less than the space in the barrel with the cap on. The most important characteristic is the thickness as force will vary with the cube of that. The length is less critical. David's simple calculator will just work off the inner diameter of the barrel, and work back to thickness on the basis of ideal number of turns and fill ratio.

S

 

[ftwizard]

I tried another mainspring that i had kicking around, but it won't wind, keeps slipping. The broken spring has a strange bridle. Do you think a standard type bridle will work as a replacement? There is no recess in the barrel, it has an impressed spot that protrudes into the barrel.

 

Edited September 11, 2016 by ftwizard

[StuartBaker104]

That sounds like you should have a hole end mainspring.  Can you post a picture of the barrel? Does it have a slot for a brace? Like here http://www.friendsoforis.com/forum/index.php?/topic/36099-watchmaking-manual-and-automatic-winding/

Having said that, I have seen a brace and hole end barrel with a regular hook end mainspring fitted.

S

[clockboy]

On 10 September 2016 at 10:35 PM, StuartBaker104 said:

You can also use David Boettcher's calculator here: http://www.vintagewatchstraps.com/blogmainsprings.php

The height of the spring should be about 0.2 mm less than the space in the barrel with the cap on. The most important characteristic is the thickness as force will vary with the cube of that. The length is less critical. David's simple calculator will just work off the inner diameter of the barrel, and work back to thickness on the basis of ideal number of turns and fill ratio.

S

 

Very useful link. Thanks Stuart.

[ftwizard]

It seems it wasn't the spring slipping, but the ratchet wheel slipping on the arbour. I did a bit of thinking at work, and come up with a theory that the spring was too big, which was pushing the lid open a little, so the arbour square section wasn't protruding enough for the ratchet wheel to grip, and so it was slipping. Well the slipping bit was right, but the rest was **BLEEP**.

I did a bit of measuring.

Inside barrel wall = 1.85mm

Edge of barrel lid = 0.38mm

Original spring = 1.64 x 0.09 x 280mm

I'm at a loss now, because according to the measurements, there should be 1.47mm free space in the barrel when the lid is in place, but the 1.64 spring fits and the lid clips down to the same height as when there is no spring in place.

What's happening? I'm losing the will to live now.

 

[clockboy]

I have not worked on this particular caliber but I presume it is an auto. The fault can be one of the following:
Spring has been wound in the wrong way around.
Spring is not hooking onto the arbour. 
No breaking grease fitted to the barrel wall.

Providing the spring is not to high the length is highly unlikely to cause an issue unless it is way,way to long. The spring should occupy approx. one third of the barrel.

[ftwizard]

It's a manual wind. The slipping problem was the ratchet wheel slipping on the arbour. That seems to have been sorted.

I'm really trying to find the best size spring for it. I'm not convinced that the one that was in it was the correct one. But the thing that is confusing me now, is that the spring shouldn't even fit in there. According to measurement, there isn't enough room, but it does fit. Weird.

[Marc]

I suspect you have a TARDIS mainspring barrel, bigger on the inside that on the outside.

Given all the other weird stuff that watchmakers have to contend with (parts pinging off into hyperspace, disappearing through worm holes only to reappear two weeks later after the replacement has been sourced, etc,) this kind of thing should be expected!! 

On the issue of the slipping ratchet wheel, was the wheel the right way up on the arbor in the first place? A lot of ratchet wheels have a recess in the middle on the top surface so if the wheel is installed upside down the engaging surfaces of the square drive hole are higher up in respect to the driving square at the top of the arbor, reducing or even completely eliminating the engagement between the wheel and the arbor.

[ftwizard]

You may be right, so all I need is a Sonic Screwdriver and I'll be made up.

Unusually, the barrel sits on top of the ratchet wheel, with no fixing screw. The ratchet wheel is flat, with no recess. So I picked the best looking side and it seems to be holding. But, I have feeble amplitude so I need to establish a spring size to move on. It also has a terrible Timegrapher readout, but that's another story.

[StuartBaker104]

You need a GR4463 or 4464. Check the i/d of your barrel, if 8mm or more, then go with the longer spring, if less, go with the shorter.