How to clean a Hermle balance unit
Start out by soaking the unit in mineral spirits for 30 minutes. I like to use old mason jars with a bent coat hanger to retreive the unit and to swish it around.
Remove the unit and turn the balance wheel 30 degrees to the right 10 to 15 times, then to the left 10 to 15 times. Slide the balance wheel up and down the wire 10 times. Put it back in the mineral spirits and swish it around to remove any loosened dirt. Dip it in out of the mineral spirits 10 to 15 times. Repeat this process until the balance wheel will continue to spin nicely.
When the balance wheel is clean enough were it will continue to spin nicely place it rubbing alcohol (at least 90%) for 5 minutes. When the 5 minutes is up take the Hermle balance unit out and shake it gently to remove any excess alcohol. Let the unit dry. After the unit is dry, spin the balance wheel. If the Hermle balance wheel spins freely for 3-10 minutes it is considered clean and serviceable.
If it does not you may need to repeat the the process or you may need a new hair spring (it is rare to have to replace the spring).
How to Identify Hermle Balance Units
Now there are two different types of Hermle balance units. There is the Hermle FSS balance unit pictured below:
Then there is the Hermle HSS (Helical Spring Style) balance unit (this is the older style) which is pictured below:
The 3-10 minute test applies to the Hermle HSS balance unit. I have not been able to find any info on the run time test for the Hermle FSS balance unit. The ones we have cleaned have an average run time of around 1 1/2 to 2 minutes.