Servicing the Seiko 6139 - Excessive Mainspring Barrel and Arbor Bushing Plate Wear

The Seiko 6139 chronograph has become very popular amongst vintage collectors. The watch shown here, being serviced for a customer, demonstrates tremendous mainspring barrel and plate wear with a bushing hole greatly out-of-round. This watch was sold as working and functioning great. It wasn’t. During 6139 design, my assumption is that Seiko may have overpowered the mainspring on this watch to support the chronograph function and the lack of a hand-winding capability like that which exists on the 6138. A side-affect of this is excessive mainspring barrel and plate wear, far more than I’m accustomed to seeing on vintage watches period much less those seeing many more decades of use. Because the wear in these can be so excessive, if a watchmaker moves-forward with this job, when facing excessive wear, by re-bushing or jeweling with a standard jeweling set and no other steps, the watch may run poorly and fail sooner after service. The best solution is a more time-consuming process known as “uprighting.” Uprighting is something you sometimes need to do on very old watches. It is atypical to require this process for a watch made in the 1970’s. Uprighting can be achieved many ways, I show one method in the lower right corner. In this process, I find the true center of the mainspring barrel arbor in the plate. If both bushings are heavily worn (top-and-bottom) and extremely out-of-round, it may be time-wise economically infeasible to find center vs replacement cost. I wish it were the case that the work involved in servicing a watch such as this were in-accordance with the money folks paid. It just isn’t the case. The time required to perform operations like this around the watch, to assure it is running well, produces cost in terms of time and parts. If a watchmaker avoids taking them on, you have a poorly running watch post-service.


Servicing the Seiko 6139 - Excessive Barrel and Plate Wear