Service: Eterna Dress Watch with In-house 905 Movement

 In Watchmaking

This is an Eterna dress watch that found its way onto my workbench. The serial number is 2892981 which places this watch in 1941.

The movement is the Eterna 905 movement. Bestfit tells me that it’s interchangeable with the ETA 825.

The two-tone dial is still in good shape but the hands are a mismatched pair of non-original ones.

Last but not least, it doesn’t run at all. So, here we go.

DISASSEMBLY

Remove all power from the mainspring before you start working on the movement. In this case, it’s extra important since the watch is fully wound. The mainspring didn’t have a chance to transfer its power because it’s a non-runner.

Move the click away from the ratchet wheel while slowly letting the crown slip between your thumb and index finger. I like to use a cocktail stick because the wood is hard enough to move the click but it’s soft enough to not leave any marks.

Remove the balance and the pallet fork with the pallet cock and store them somewhere safe.

Eterna with Eterna 905 movement

Balance and pallet fork removed.

When I checked the moving wheel train from the side, I noticed that the 3rd wheel was very wobbly. I always write my findings down to investigate or sort it out later.

Lift the cannon pinion on the dial side of the movement. It’s easier to do it now than with the wheel-train bridge removed. You won’t be able to lift the center wheel with the cannon pinion in place.

Lift the wheel-train bridge and remove the crown wheel and the ratchet wheel. This will make it easier to lift the center wheel.

The crown wheel screw is left-handed although it’s not marked as such so be careful.

Eterna with Eterna 905 movement

Lift the center wheel, third wheel, fourth wheel, and escape wheel. I noticed that the 3rd wheel was wobbly because of a bent top pinion so I ordered a new one.

Eterna with Eterna 905 movement

Disassemble the click and the click spring and lift the barrel bridge.

Take out the barrel.

 

Eterna with Eterna 905 movement

Flip the movement around to work on the bottom plate.

Eterna with Eterna 905 movement

Bottom plate with a heavily tarnished minute wheel.

Remove the motion works and the keyless works. You can clearly see that the minute wheel is corroded. I ordered a new one because it caused friction with the set lever spring.

Pre-clean the pivot holes and bearing jewels with a peg wood. Don’t forget to remove the bottom balance end stone to clean it separately.

During the inspection of the mainspring, I noticed that it’s probably still the original mainspring. At least, it’s an old one because it’s a blue type without the S-curve.

Eterna with Eterna 905 movement

Old blue mainspring without the S-curve. You can tell it’s “set” because it roughly stays in the same shape if you take it out of the barrel.

Clean all the parts in the watch cleaning machine.

ASSEMBLY

Fit the barrel (with the new mainspring), the escape wheel, the fourth wheel, the (new) third wheel, and the center wheel.

Eterna with Eterna 905 movement

Install the wheel train bridge.

Eterna with Eterna 905 movement

 

Install the barrel bridge, the crown wheel, and the ratchet wheel. Don’t forget the bushing for the crown wheel.

Eterna with Eterna 905 movement

The wheel train spins freely without any friction and the third wheel isn’t wobbly anymore.

Turn the movement around and fit the motion works and the keyless works.

Eterna with Eterna 905 movement

Flip the movement to the top plate and reinstall the pallets.

Wind the watch a couple times to check the pallet fork. If the wheel train spins freely, the pallet fork snaps to the other position with the lightest touch.

Place the balance in position and the movement should come alive. It might need a little flick to jumpstart it.

Sadly, the movement doesn’t keep accurate time. In fact, it’s all over the place.

Obviously, the movement does run and it has a decent amplitude in the dial down position. However, it runs much too fast.

In the dial up position, the timekeeping is horrible.

The wheel train spins freely and the pallet fork snaps with the lightest touch. That means that the problem is with the balance.

If you look closely, you’ll see that the hairspring is kinked to the left of the regulator and the distance between the windings on the left are smaller than those on the right. My guess is that someone tried to move the regulator while the regulator pins were too tight. That caused a kink and distorted the whole hairspring.

The balance complete for the Eterna 905 and ETA 825 are obsolete and I can’t find any on eBay. That means that the hairspring has to be manually manipulated.

Unfortunately, this is way beyond my skills so I don’t feel comfortable doing that. Especially without a safety net in the form of a new balance complete.

This one has to be repaired by an experienced pro. It sucks but that’s just how it is.

Do you also have fits of crying because of problems with the balance or hairspring? Let me know in the comments below.

Recommended Posts
Showing 4 comments
  • Gero Gaedeke
    Reply

    May this video can help you to repair the hairspring yourself: https://www.youtube.com/watch?v=uvMCNyrDZQo

    regards
    Gero

    • Melvin Hollenberg
      Melvin Hollenberg
      Reply

      Thanks for the effort. However, Mr. Lovick is a very experienced professional watchmaker. Seeing him do it on YouTube and doing it yourself are two very different things.

  • Remo A.Peter
    Reply

    “I noticed that the 3rd wheel was wobbly because of a bent top pinion so I ordered a new one.” Does that mean, you have been able to obtain it from one of the parts wholesalers? Wow, for a 1941 watch…

    • Melvin Hollenberg
      Melvin Hollenberg
      Reply

      Yes, from Cousins UK. I had to order it for the ETA 825, but they’re interchangeable.

Leave a Comment

How to choose the right mainspringGerman watches