How to Clean a Hermle Clock Movement
First we need to remove the balance unit. This is done by carefully removing the two screws on the front of the Hermle balance unit. Put them in a ziplock plastic baggy (I like to use plastic baggies whenever I disassemble a unit as it keeps you from loosing parts, it keeps them clean and it helps with reassembly as you just go in reverse sequence).
Next tip the balance unit towards you (being carefull not to hit/damage the fork) and remove.
Next we need to remove the barrel springs (this is very easy to do on a Hermle movement). Now we remove the pressure on the springs (THIS VERY IMPORTANT AS FAILURE TO DO AS DIRECTED CAN RESULT IN SERIOUS DAMAGE TO THE MOVEMENT AND TO YOU!!!). You will need a "let down tool" in order to do this. If you dont have a let down tool you can make one easily using a broom handle, dowel etc...
All a let down tool is a piece of wood that has a slot cut in one end, here is a video:
OK once we have let down the springs we will remove them. On the Hermle 341-020 you will have to remove the hammers, this is a simple process as there are only 4 screws that hold it in place. But before you remove the screws, disconnect the the arm that contols the hammers.
You will also want to have a couple of rubber bands handy as you will put them on the plates of the hammer assembly when you take it off (DO NOT SEPERATE THE PLATES as they are a pain in the ass to put back together correctly) in order to keep the hammer assembly intact. Here are the pics of the screws:
Next we remove the screw holding the click lock(see below).
With the screw removed just pull up on the arbor and remove it, the mainspring will slide out now. Put the click lock, arbor, screw and barrel spring in your plastic bag and make sure you label which train (time, strike or chime) you removed it from. This is very important as Hermle clock movements routinely have different sized springs on the same movement.
With the mainsprings removed you now have a few different options on how to clean the Hermle movement. You can continue to tear it down and do a full blown overhaul or you can go ahead and start to clean the gears/pivots now. For the purpose of this article we are going start process of cleaning the gears and pivots as 75% of the time this will solve the problems you are having with a dirty movement.
There are some options when it comes time to letting the movement soak I will let you decide which one works best for you. Which ever method/solution you decide to use, I do suggest that you only let it soak for a short period of time intially until you are confident in how the solution works with your movements. As far as cleaning solutions go, you have your standard watch/clock cleaning solution you can pick up online and in the clock repair shops. I have also heard of people using the following but will let you explore these options on your own: Naptha, Simple Green, Kerosene and some home brew solutions are available on eBay.
As far as the actual cleaning process after your movement has soaked, make sure you use some pegwood, toothpicks or a brush and clean out all the loosened up crud from around the pivot holes and gears. You can put the movement in an ultrasonic cleaner (Herbor Freight has them for about $60- $80) or a big pot with some simmering water/solution. You will have to experiment with these and find which process works best for you.
When you are satisfied the movement is clean, immediately rinse it off thoroughly under hot water. When you are done rinsing it make sure you dry it quickly, some people have used hair dryers, ovens, and I prefer using an air compressor to blow out the water. Now just reinstall your springs, hammers and balance wheel (if applicable) and apply oil to all your pivots. Hopefully you have just given your "old broken Hermle movement" a new life!