Antique Clocks/Mainspring for Bentima mantle clock
My Mother has a Bentima 8 day mantle clock (circa 1974)that once wound, only runs for a short time and then dies. My Father believes it needs a mainspring, which he is confident that he can install himself without compromising the integrity of the clock. The markings in the clock say made in West Germany; 71-340-020. When my Father took it to have repaired, the fellow wanted to rip all the guts out and basically change all the insides to new, which mu Father declined. Is there anywhere that you know of where I can send away for the proper part? My Mother loves that clock and it has great sentimental value. Thanking you in advance.
Weak springs do not very often occur on spring driven clocks. However, sometimes the springs will break. When this happens you can keep turning the key and it will never tighten to where you cannot turn the key any further. In that case, you will certainly need a new spring.
Merritts (www.merritts.com) has springs already loaded in the barrel for this particular movement. I am assuming this is a Hermle hair spring and balance wheel movement (this requires no pendulum). The price of a new spring in Merritts catalog is $28.00 plus SH. They also sell the complete movement. The price is not quoted in the catalog due to variations in the Euro. When disassembling the movement, observe very csarefully the timing of the gears on the strike side as these are very critical. Also be careful of the hairspring so as to not damage it. Be certain all of the springs are completely run down by tripping the chime and strike trains until they will not run anymore. On the time side, there is probably little energy left in the springs if the spring is broken. After you have run the trains as far as they will unwind on their own, insert the key in each arbor and turn it in the winding direction enough to release the pressure off the rachet clicks. Pry the rachet clicks up slightly and allow the spring to rotate the key while you gently hold it back. Do this until the spring is completely relaxed. Be certain to do this on all three springs.
Hermle movements are used in many clocks as there are many case builders and relatively few manufacturers of movements.
Having springs replaces is usually expensive because of the extensive amount of labor required to disassemble and reassemble a clock with a Westminster chime movement. Replacing the movement may actually be cheaper than paying the labor to have it done.
I assume the clock has been oiled as this will give a similar symptom. There is also a possibility there is quite a bit of wear at the pivot points and the Staffs (shafts) are locking in the worn holes. However, it does sound like you have a broken spring which will have to be replaced.
Feel free to contact me if you have any problems with doing the repair.