Floating balance movements began appearing in mechanical clocks in the early to mid 1950s. The floating balance has advantages over pendulum clocks. It is robust and not susceptible to disturbance and will tolerate being out of level.
This movement came out of a Dugena sixties era Mantel clock and is an unmarked Hermle. When I first received the clock the seller told me that it loses time and might just require a simple adjustment. Where have you heard that before? How about, it’s worn out. The clock has been completely disassembled, cleaned, reassembled and oiled eliminating any issues in the time and strike train.
It continues to run slowly and the culprit appears to be the floating balance escapement. To function properly the balance wheel spins back and forth and therefore maintains the beat of the clock through a simple and usually reliable pallet fork assembly. Adjustments are minimal. There is a speed adjustment and once you have played with that enough and the clock continues to lose time you must look elsewhere for the problem either with the trains or the escapement itself.
The floating balance assembly consists of a balance wheel, 2 jeweled bearings on each end of a hollow tube riding on a pivot wire supported in a u-shaped frame.
The most common reasons for sluggish balance performance are dirt, rust / pitting / roughness of the wire, bent or weak wire or excess oil on the wire & jewels.
Removal is simple – two screws, tilt the balance to avoid bending the pallet fork and pull out. Here is the assembly removed from the movement. Almost immediately, you can see that the helical hairspring appears to be distorted. Ideally it should enclose the balance shaft perfectly.
So, it is functioning as it should? The balance wheel should float on the wire that goes through the cylindrical shaft. Though somewhat exaggerated it should looks something like this (next photo) if it functions as it should. In this position a push the balance wheel should allow it to rotate freely for a minute or more.
When in a level position the balance wheel in the Dugena mantel clock looks like this. Not good! You can see that the cylindrical shaft that the thin wire is suspended within is actually resting on the banking forks (or base). In this position the shaft is resting on the base and the resulting additional friction slows the rotation of the balance wheel and ultimately slows the clock down.
So, what to do? In this case either the jewels are cracked or the spring has lost its strength. The solution; find a new helical torsion spring, find a new / identical balance wheel assembly or a suitable but newer replacement.
I have spent some hours on this movement and have come to the conclusion that it is probably not worth spending money on it unless I can find a donor movement for a cheap price. Luckily I did not spend much for this clock in the first place.
I hope this is a good explanation of a floating balance or in this case a floating balance that is drowning.