Service: Onsa Dress Watch With an FHF 72 Movement
Sometimes you need a bit of luck. I found this beauty in the pile of broken donor watches. No idea what it was doing there, but it sure was a nice surprise.
It’s an Onsa dress watch with an FHF 72 movement. It doesn’t have an Incabloc shock protection system, so it’s probably from the late 40s or the early 50s.
Let’s dive in.
Remove all power from the mainspring. Move the click away from the ratchet wheel and slowly let the crown slip between your thumb and index finger.
Remove the balance assembly, the pallet cock, and the pallet fork.
Flip the movement and remove the minute works.
The minute wheel and the minute work cock both show extensive signs of wear and rubbing, so the minute wheel has to be replaced. I’ll use some multi purpose oil and Bergeon polishing powder to polish the minute work cock.
Flip the movement back around and remove the ratchet wheel and the crown wheel with the bushing.
Remove the train wheel bridge and lift the escape wheel, the sweep second wheel, and the third wheel.
One reason that the watch didn’t run is that someone tried to use the wrong escape wheel. See the picture below.
This part comes in 4 different versions:
- for a movement with two end-pieces
- for a movement with a lower end-piece only
- for a movement with an upper end-piece only
- for a movement with straight pivots
The correct escape wheel for this movement is one for two end-pieces. Sadly, this version is obsolete so I bought a donor movement with two end-pieces on eBay.
Remove the barrel bridge and lift the barrel.
The barrel has a dent in the cover which may interfere with the mainspring. See the picture below.
I replaced it with the barrel and cover from the donor movement with a new mainspring.
Remove the center wheel cock and lift the center wheel.
Flip the movement to the bottom plate and remove the keyless works.
Pre-clean the pivot holes and bearing jewels with a peg wood. This way, the hardened grease and dirt are removed as much as possible to be cleaned more efficiently.
Clean all the parts in the watch cleaning machine. Six minutes per bath and the heating chamber will do the trick.
Start with the lower cap jewels with the end-pieces for the balance and the escape wheel. It’s a good idea to also reinstall the set lever at this point.
Flip the movement to the top side. Place the center wheel in position and install the center wheel cock.
Place the barrel (new barrel + lid + mainspring) in position and install the barrel bridge.
Reinstall the click and the click spring.
Place the third wheel, the sweep second wheel, and the escape wheel in position.
Use the automatic oiler to lubricate the upper end-piece for the escape wheel and reinstall the train wheel bridge.
Reinstall the ratchet wheel, the crown wheel ring, and the crown wheel.
Flip the movement around and reinstall the keyless works and the minute works.
Start with the winding stem, the cluth wheel, and the winding pinion. Place the yoke in position and reinstall the yoke spring and the setting lever spring.
I used the minute wheel from the donor movement and the underside of the minute work cock has been polished.
Flip the movement around and replade the pallet fork and the pallet cock.
As soon as you place the balance in position, the movement should come alive.
Place the hour wheel and dial washer in position, fit the dial and recase the watch.
What do you think of this Onsa dress watch? Do you have one yourself? Let me know in the comments below.