Hamilton 940

[Nobby]

Would anyone know what the difference is between a Hamilton 940 balance wheel 242a single roller & a 242b double roller (just the wheel no other parts added)

Thanks

 

Edited January 17 by Nobby
typing error

[JohnR725]

33 minutes ago, Nobby said:

just the wheel no other parts added

if it's just the balance wheel according the parts list it's just the balance wheel there is no difference. 

 

[nevenbekriev]

I am not sure if You ask correctly what You need to know. The balance wheel is the same, but the balance staffs are different. You can not get balance with single roller, take the roller out and put double roller or vice versa. If You need to switch the rollers, then balance staff has to be replaced too.

[Nobby]

yes I appreciate what you say , because in the chart it states balance complete s.r 242a & 242b d.r. was unsure if there was any difference between the wheels

I wanted to use a wheel from a single roller 926 on a 940 double roller I know the staffs are different as are the roller tables was not sure if the 940 had more balance screws

[nevenbekriev]

As long as You use the hairspring that goes with that balance wheel, You will not have to worry about the screws and their count. You should use wheel and spring as a pair  and never separate this pair. Of course, the BPH of donor balance/hairspring couple must be the same.

[JohnR725]

7 hours ago, nevenbekriev said:

I am not sure if You ask correctly what You need to know.

to be honest I wondered about that but often times when I quiz newbies questions to clarify they get mad at me so I just answered the question as it was asked

6 hours ago, Nobby said:

I wanted to use a wheel from a single roller 926 on a 940 double roller

then that's not what your original question was. as this is now the first time you mentioning 926. then there's the minor problem of the parts book the balance wheel seems to be a different part number?

 

6 hours ago, nevenbekriev said:

You should use wheel and spring as a pair  and never separate this pair

typically in watch repair this answer is correct 99.8% of the time. But typically any time you have a Breguet Overcoil Hairspring it was premade. This is so they get all the curves and everything in exactly the right place. then typically on 99 point some odd percent of balance wheels they hairspring is vibrated to that exact balance wheel. Which is why the parts are not available separately. If the parts are available separately like in this case then the balance wheel has to be matched of the hairspring with timing screws. The factory had a infinite supply of variations and at one time when the hairspring was available separately you could buy a timing screw assortments. So basically since you can't get timing screw assortments you do want to keep the balance wheel and hairspring together. Plus there's the other little problem?

The parts books can be tricky with part numbers in that there can be variations for the exact same part number. Especially if things were made over time there will definitely be variations

so for instance both balance wheels use a number 75 hairspring which would imply that the same but they're not typically because hairsprings come in different strengths. Which is explained in the image below it depends upon how heavy the balance wheel is. So not only does the hairspring and balance wheel have to be matched for frequency it also has to be the right hairspring for the weight of the balance wheel. Which is why we recommend not mixing and matching hairsprings.

Also when swapping components anything related to the escape but it's best if you can keep everything with one watch with that watch otherwise you're going to have to adjust things to match the new parts because the probably be a slightly different size. For instance that's why they have movable banking pins to make up for differences on every single watch as they were manufactured. So it's really best not to mix and match American pocket watch components if you can do that. Plus if you look carefully on your balance wheel it actually has the serial number scribed on it as it was made for a specific watch even if the parts book indicates you can mix and match