One of the most important steps when servicing a mechanical watch movement is to thoroughly clean all of the parts to remove all traces of debris, oil residue and other contaminants from the surface of the parts.
Cleaning movement parts is necessary for many reasons, firstly a clean movement will keep time more reliably, one of the most common reasons for a watch to keep poor time is the hairspring becoming contaminated. A clean movement will also look more appealing particularly when showcased in a watch with a display case back. It is also important to thoroughly clean the movement to preserve the lifespan of the movement, over time the contact points between moving parts of the movement will wear down producing microscopic grit-like particles. If these particles are not periodically removed, these grit-like particles can exponentially increase the rate at which the moving parts wear, reducing the lifespan of the watch. Lastly thoroughly cleaning the watch movement will prevent the movement from tarnishing discolouration. Often movements will contain parts that are made of brass and steel that can discolour if they are not correctly cleaned, or not cleaned at all.
Many professional watchmakers will use a watch cleaning machine or an ultrasonic cleaning bath to clean the movement components. Whilst these methods yield exceptionally clean parts and consume little of the watchmakers time, for the hobbyist, investing in expensive cleaning equipment is not necessary.
Most hobbyists will resort to cleaning the movement by hand using a selection of cleaning solvents. Personally, I use two different cleaning fluids to clean the parts. The first fluid is simply washing up liquid (detergent) diluted with distilled water (approximately 1 drop of washing up liquid to 100ml of distilled water), the other is 99.9% pure isopropyl alcohol. I have had great results using these fluids, although many prefer to use lighter fluid or specially formulated cleaning fluids. No matter which cleaning fluid you choose to use, the same basic cleaning procedure should be used.
It is important to only attempt to clean a watch movement that has been fully disassembled.
Whilst this method work for most of the parts, there are two components that should not be cleaned using this method, these are the pallet fork and the balance assembly.
The basic method involves cleaning the parts, followed by two rinses and then thoroughly drying the parts.
The first step involves letting the parts soak in the first cleaning fluid for several minutes, then using a small paint brush to agitate the surface of the parts in order to remove any stubborn contaminants. I use distilled water and washing up liquid for the first stage. If you have an ultrasonic cleaner at your disposal, you can use the ultrasonic cleaner during this step, instead of using a paint brush to agitate the parts. You may find it helpful to load the parts into a cleaning basket or a small sieve so that it is quicker to transfer the small parts between the various cleaning fluids. It is important to place the larger items in the solution before placing the smaller more delicate parts in to avoid damaging them.
It is important to use distilled water to clean the parts rather than tap water as distilled water does not contain any contaminants that will leave a residue on the parts. It is also important to not use excessive amounts of washing up liquid as you may find using large quantities of detergent will leave a residue on the parts and does not increase the cleaning power of the solution. Approximately one or two drops of washing up liquid for every 100ml of distilled water should be more than sufficient. You may find that heating the distilled water may enhance its cleaning performance as the heat will soften any oil deposits and will increase the rate of reaction between the soap and the oils. Warm soapy water is a very effective at cleaning watch parts as the warm water will dissolve any salt residues and carry away any dust and debris, and the soap will break down any oil residues.
After cleaning the watch parts in the first solution, the next step is to transfer the parts to the second cleaning fluid, for which I use 99.9% pure isopropyl alcohol. Isopropyl alcohol is a particularly useful cleaning solvent as it both dissolves any grease or oils that were not removed in step 1 and also removes any traces of the first cleaning solution from the parts.
There is no need to dry the parts when transferring them to the next solvent, however blotting them on a paper towel to remove the majority of the first solution is recommended. I usually submerge the parts in this solution for 5-10 minutes. Whilst these parts are submerged, a small brush should be used to agitate the surface of the parts to aid the cleaning process. You may find it helpful to steady the parts with a piece of pegwood whilst you are agitating the surface with a small brush.
Pegwood should be used to clean the pivot holes of the bridges and mainplate, the pegwood should be sharpened to a point and placed inside the pivot holes and then rotated. This will remove any contaminants from the pivots. It may be necessary to repeat this step several times for each of the holes, sharpening the pegwood with a knife between cleanings to remove the soiled wood. Pegwood can also be used to remove any fouling that has not been dissolved by the cleaning solutions. You may find it easier to remove the bridges from the cleaning fluid to clean them and then place them back in the cleaning fluid to soak for a few more minutes.
By this stage, the parts should clean, however, it is common practice to transfer the parts to one more cleaning fluid to remove any traces of residue. Again it is recommended that the parts are blotted before transferring them to the third and final solution. For the third cleaning fluid, again I use 99.9% pure isopropyl alcohol, although lighter fluid can also be used. The benefit of using alcohol over lighter fluid for this step is that pure alcohol will not leave a residue on the parts, whereas lighter fluid often contains traces of oils that will leave a residue on the parts. Again I leave the parts to soak for 5-10 minutes in the cleaning fluid.
Now that the parts are clean the next step is to dry each part. The parts should be removed one by one from the cleaning fluid using tweezers, placed on a clean sheet of blotting paper and then dried using an air blower.
The parts should be dried one at a time, and after drying, each part should be inspected for cleanliness and then stored in a container with a dust cover to prevent the freshly cleaned parts from becoming contaminated. Any parts that are not completely clean should be cleaned again using the same process. If you are finding that multiple parts are still dirty, consider changing the cleaning fluids with fresh fluids, or use a different type of cleaning fluid. Allowing the parts to soak for a longer period and agitating the surface will also improve the cleaning results.
The balance assembly and pallet fork contain jewels that are retained using shellac. Shellac can be dissolved by some solvents, namely ethanol (methylated spirits), whilst in theory, it is safe to clean these parts using the same method as the other parts, I take extra precautions to avoid any damage from occurring. I clean these parts using lighter fluid, I soak them for a few minutes then carefully agitate the surface and then transfer them to a second container of lighter fluid to dissolve any residue.
Take extreme care when removing the balance assembly from the cleaning fluid as the hairspring, part of the balance assembly, is extremely delicate and can be deformed if the balance assembly is removed from the solvent without supporting both the balance bridge and the balance wheel. This is because the surface tension of the cleaning fluid will weigh down the balance wheel and this can stretch the spring if the balance assembly is not correctly handled.
After soaking these parts in the second cleaning fluid they then need to be dried thoroughly, the same method is used to dry these parts as all other parts.
Once all of the parts have been cleaned and thoroughly dried, the movement can be reassembled and lubricated.