I have a Bolova 340-020 mantle clock and it loses about 10 minutes per day. How do I adjust that?
The 340 movement is made by Hermle. They put names of companies on the movements if they purchaced a certain number of them, as Bulova did. There were two types of regulators used on the 340. The earlier ones were the floating balance type that had a vertical spiral spring, and the balance wheel type that had a horizontal hairspring. You will find these regulators on the top back of the movement. If you contact me at my email address below with the type you have, I will send you some information for setting it. I also need to know some history of the problem. Have you just acquired the clock or have you had it for a while and the change in regulation was sudden or was it over a period of time? Also, 10 minutes a day might be excessive for an adjustment, as it could be a defect in the regulator. If there is oil on the coils, magnetism, debris in the pivots, the regulator might have to be serviced and sometimes replaced.