Jump to content
Sign in to follow this  

Modding the Rotor of the Hublot Big Bang

Recommended Posts


Another Francisco DIY.


On the web page of Hublot it is possible to download a pdf file where it is explained how to detect a rep of the Big Bang model. Follows some pictures taken from this document.





As seen, following Hublot, we have to check three things:


a) Absence of regulator. Well, now this is not true, as the versions running at 21600 have a regulator (not functional). If we buy a version running at 28800 (BTW I think they are a better option) there will be no regulator. However, I explained here how to add a regulator:



b and c) There are two versions of rotors in the rep market. One, with good ball bearing, but using sticks on the rotor mass. And another version with saw-like ball bearing but with engraved rotor. No version is perfect, so modding has to be made. About modding the H… I am working on that.


Some examples of reps:


The watch I bought, rotor engraved, bad ball bearing. There is no H under the rotor.



And follows one example with good bearing, but with stickers (and of bad quality). In addition, the screws never can be blue! They only can be black of with no colour (silver).




Therefore, modding on the rotor has to be made. In my opinion, the best option is to buy a rep with engraved rotor and modifying the ball bearing. After that, adding an H (future tuto) and adding a regulator, will produce a very good rep of this watch.



Needed Materials


As a minimum, you have to buy the ball bearing of the ETA/Valjoux 7750 and the external bolt. Follow the prices of these two parts and the references for Cousins web store:


VAL77501497 Valjoux 7750 1497 Ball Bearing £5.95

VAL77501491 Valjoux 7750 1491 Oscillating Weight Bolt £2.00





First step is to remove the rotor from the movement and to take out the bearing that the rep has. The bearing is press assembled and, therefore, to remove it a press is necessary. I used a press to assemble / dissemble crowns and chrono tubes. Is it really necessary to have this press? No, but it is highly recommended. If you make this task without a press, please be careful, as you can deform the rotor. In such a case the rotor will not turn freely.


Follows a picture of the rotor after being dissembled from the movement:




A picture of the press:




The widest pressing tool is placed on the press and we screw carefully:




The bearing is free:




These are the gen ETA parts to be employed: the ball bearing and the bolt.




As seen, the bolt I received is golden. Probably you can obtain the silver version from another source. However, the golden layer can be removed very easily.


You only have to remove the golden layer form one side. Both sides are equal. A piece of Cape Code or similar will do the job. Do not file…




After few minutes of work…the bolt is silver.




To understand the steps to do in this modification we have to understand how the ball bearing is assembled in the gen ETA 7750. We have to understand that we cannot follow the same procedure.


This is a gen rotor when the 7750 is bought alone.




As seen in the picture, the bolt is rotated a bit in comparison with the ball bearing. The arrows show the faces that were together, before the rotation of the bolt. When the bolt is rotated fastens the bearing against the rotor. The bolt moves down the upper face of the bearing.


To assemble and dissemble the bolt (to rotate it), a special tool (quite expensive) is employed, as seen in next picture.




Next picture shows the bolt and the bearing after being dissembled. The picture shows that the ETA rotor has a circular sunken area where the bearing and the bolt are assembled. This area is not present on the rotor of the rep!




Let us study with detail how the bolt fastening method works. As the next picture shows, the ETA bearing has a groove. This groove is for the bolt. Therefore, thanks to this groove, the bearing is fastened on the rotor.




However, when the ETA bearing is placed on the rep rotor… the groove is not visible, see next picture. Therefore, the bolt cannot rotate under the bearing.




Therefore, two options are available. 1), we remove material from the rep rotor. This is hard to do with precision, and we have to be very careful not to damage the black paint of the visible parts of the rotor. 2) to glue the parts on the rep rotor. I decided to glue the parts. It is more practical, although less rigorous.


I used Araldit Epoxi fast dry. A small quantity is placed on the bottom part of the rotor.




And the ball bearing is glued. Do not worry about the bearing. It will not be lost. LThe glue used is very hard and the bearing is not receiving hard strength. Really, DO NOT WORRY.




Next step is to glue the bolt.




As a small problem, the bolt is not rotated against the bearing. However, it is very hard to see that, if possible. Check the last pictures on this tuto.


The last step is to remove the black paint of the 4 holes that the bolt has, with a needle or similar. Next picture shows this process, before all the black paint is removed.



If you prefer you HBB with silver screws, I checked that the gen ETA screws are compatible. Or you can remove the black paint of your black screws using acetone. Do not worry, as the Hublot documents says, first versions of HBB employed black screws, as next picture shows.





Share this post

Link to post
Share on other sites

nice pics.I wish I knew how to work on watches. :Whistle:

Share this post

Link to post
Share on other sites
Member X

That's an awesome guide, thank you for taking the time! ::D

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this