How do I Replace a Main Spring on a Broken Mechanical Wrist Watch?

Written by rob wagner
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How do I Replace a Main Spring on a Broken Mechanical Wrist Watch?
Replacing a mainspring on a mechanical watch is difficult. (pocket watches image by Andrew Breeden from Fotolia.com)

The mainspring on a broken mechanical watch can't be repaired, and will require replacing in order for the watch to operate properly. If you plan to remove the mainspring, be prepared to disassemble the entire movement, which is the tiny engine the runs and regulates mechanical watches. Be prepared to oil and clean the movement if you plan to disassemble it. The job, however, is not for novices, and requires specialised tools. Consider taking a watchmaking course at an adult vocational school.

Skill level:
Easy

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Things you need

  • Case blade
  • Watchmaker's rubber ball
  • Jeweller's loupe or magnifying glass
  • Toothpick
  • Watchmaker's precision screwdriver
  • Hands-grabber removal tool
  • Eighteen-egg egg carton
  • Tweezers
  • Watchmaker's hand vice
  • Naphtha
  • Shot glasses
  • Toothbrush
  • Lubricant
  • Oiler
  • Mainspring
  • Digital camera

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Instructions

  1. 1

    Pop open the snap caseback with a case blade by wedging the blade between the case and caseback and pushing the blade down. For a screwdown caseback, place a watchmaker's rubber ball on the caseback and rotate it counterclockwise until it's free.

  2. 2

    Use a jeweller's loupe to locate the mainspring. It's a tightly coiled thin ribbon of steel inside a small cylinder known as a mainspring barrel. Wind the crown, which is the winding knob on the case edge at 3 o'clock, a couple of notches. Note the stem of the crown has a metal ledge "clicking" over the big gear called the mainspring ratchet wheel.

  3. 3

    Rotate the crown a couple of notches with your left hand. Nudge the metal ledge away from the gear with a toothpick in your right hand. The mainspring will unwind.

  4. 4

    Locate with a jeweller's loupe the two tiny screws that fasten the movement to the case. Loosen the screws counterclockwise using a screwdriver. Remove the movement from the case. Place the screws in an egg carton compartment.

  5. 5

    Turn the movement over. Place the feet of the hands-grabbing tool on the dial over the centre post. Use the hands-grabber to remove the hour, minute and second hands from the post.

  6. 6

    Use a screwdriver to remove the dial from the movement by loosening the two screws that attach the movement to the dial.

  7. 7

    Locate the hour wheel, which is a brass gear. Remove it with tweezers. Remove the smaller gear attached to a post. This is the cannon pinion. Gently pull it off with a watchmaker's hand vice. Use a screwdriver to loosen the screws to remove the two or three bridges, which are flat pieces of metal.

  8. 8

    Use a screwdriver to remove the screws to the barrel bridge. Use the tweezers to remove the gears. Remove the mainspring barrel and the mainspring. Remove the jewels, which are tiny coloured stones, from their pinholes. There will between seven and 25 jewels.

  9. 9

    Place all parts in the egg carton compartments. Label each part. Pour Naphtha, which is a lighter fluid solution, into a shot glass. Place each part in the shot glasses and let them soak. Use a toothbrush to clean especially dirty parts. Use an oiler to lubricate the jewel pinholes. Let the parts air-dry once cleaned.

  10. 10

    Repeat Steps 4 through 8 in reverse order. Don't forget to use your new mainspring in the reassembly. Wind the watch when the caseback is completely closed.

Tips and warnings

  • Photograph each step and label each part on the egg carton compartments to aid in the reassembly.
  • Never force anything. You will break delicate parts.

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