Water Resistent Crowns
Replacing the crown on a wristwatch is actually pretty easy. There are basically 3 types of crowns for wristwatches: plain, dustproof and water resistant. They come in a variety of diameters and thickness. The crown screws onto the stem which is the thin shaft that inserts into the watch movement. Watch cases requiring a water-resistant crown will have a pipe coming out of the case through which the stem fits through.
Plain crowns have a plain inner surface which sits close to or on the surface of the case. This are not used on modern watches but can be found on vintage watches through most of the 20th century.
Dust resistant crowns
Like plain crowns, dust resistant crowns are not really used today but were popular in the 20th century. They usually have a sprung skirt that fills the gap between the crown and case. Like the plain crown they are not resistant to water.
Water resistant crowns come with an “O” ring. The size of the “O” ring is based off the diameter of the groove it sits inside that is on the stem. Always replace an “O” ring with the same type or shape.
When installing a new: “O” ring or gasket make sure that all the surfaces are completely clean and free of dirt. Wipe a layer of silicon grease over the “O” ring before installing it.
There are a few methods for sealing the crown. Some have a “O” ring on the inside of the crown that makes a seal. In the picture above on the right, the “O” ring is on the inside of the crown and seals against the outside of the pipe in the case that the stem passes through. If this “O” ring is damaged, it is best for you to replace the crown. This is the most reliable way for you to ensure a proper fit.
Another approach uses an “O” ring that you fit on the projection of the crown where it goes into the pipe of the case and seals against the inside of the case pipe.
Rolex Pioneered the screw down crown. Variations of their design are standard today on all dive watches. Manufactures thread the outside of the case pipe as well as the inner surface of the crown. When you unscrew the crown, a spring in the crown pushes it away from the case pipe. This allows you to wind the watch without the threads engaging.
Inside the crown is a seal. When you push the crown in to screw it down, you compress the gasket in the crown against the pipe in the case making in watertight.
How a Diver Crown Works
As you can imagine the divers crown is a lot more complicated than a regular or dust proof crown.
Depending on the manufacture, the crown usually has two parts. The inner part, screws onto the stem. The outer part is free to move inwards against the spring when its screwed down.
There is a “clutch” arrangement to let the crown, when unscrewed, to turn the stem. Two slots, in the central portions of the crown engage with a corresponding projection at the upper end of the winding stem. The crown and stem become ‘keyed” together. The crown, now clear of the screw on the pipe, will turn the stem to wind the watch or set the time.
When you screw the crown down, the “clutch” becomes disengaged. This allows you to screw the crown down and seal to the case pipe.
Selecting a replacement crown
Luckily, parts for crown and stem replacement are readily available. When selecting a new crown, the thread size or “tap size” of the hole in the crown is important. The four most common sizes are 0.6, 0.7,0.8 and 0.9. This refers to the approximate size of the outer dimensions of the threaded part of the stem. Measure the threads of the stem with a micrometer or caliper to determine the correct “tap” size needed for the new crown.
Removing the stem from the watch
With a pair of tweezers or small screwdriver gently push on the button while pulling out on the crown and stem. This button is usually near the stem. This button will spring back into position when the stem is released.
Some movements use a screw to hold the stem in place. This is known as the setting lever screw. Turn it no more than one turn while pulling out on the crown. This is usually enough to release the stem. If the stem does not release, turn the screw another ¼ turn and try again. You must be careful when turning the screw. If you turn it too much, the hand setting mechanism under the dial will come undone. If this happens you will have to partially dismantle the watch to re-assemble it.
Unscrewing the crown from the stem
Hold the stem is right below the threads on the stem. If you hold the stem on any other part, the chance of breaking the stem is almost certain.
Usually, you will be able to remove the crown with firm finger pressure. If it will not unscrew using firm finger pressure, gently heat the crown with a small hot air gun. This will soften any adhesive that has been previously the threads. It will also expand the metal slightly which will help release the threads.
Dealing with a broken stem
If you have a broken stem, you will need to source another. If you have the specification sheet you can use it, along with the caliber number, to source a new one. Stems are not interchangeable from one caliber to another. Stems cloned calibers are not compatible either. You must source a new stem from the exact caliber you are working on.
Sometimes you may need to reuse the existing crown, but the stem has broken off inside the crown with nothing to hold onto to remove the stem. You can use a hot mixture of Alum powder mixed with water to soak the crown in to dissolve the steel stem from inside the crown. If the crown is brass or aluminum, the alum will not damage them. If the crown is steel, you are out of luck. You can use a magnet to see if the crown is steel or not. Of course, with a diver crown that has a steel spring, Alum is not the answer, and you will have to source another crown.
Refitting the crown to an existing stem
Make sure the threads on the stem are clean and apply a drop of low-strength adhesive to the tip of the threaded tip of the stem. Holding the stem in the pin vise as before, screw the crown back on firmly but not overly tightened.
Refitting a crown to a new stem
If you have sourced a new stem it will need to cut to size. If your crown is a water-resistant screw down crown, start by threading the crown onto the pipe. Remember that the pipe on the case needs to seal with the gasket in the crown. Tighten it down but do not over tighten it. Look at the position where the crown sits to the case. Is it flush or is there a small gap? Looking at it under magnification is best.
Screw the crown onto the new stem finger tight. Install the stem back into the movement. Test the winding function to make sure it is fully seated into the movement. with a pair of calipers measure from the underside of the crown to where it meets the case. Record this measurement. Remove the stem from the movement and the crown from the stem. Holding the stem with a pin vise as before, measure from the tip of the stem down and make a mark on the threads.
Cut and Fit the New Stem
Using a pair of flush cut pliers, cut the stem 0.2 above you mark. Use a fine # 2 or #4 file and gently file the tip of the stem smooth. You can also use a fine piece of sandpaper to gently smooth the tip as well if you do not have a file. Just make sure to remove and bur that may be on the tip of the stem. Make sure the stem is clean and screw the crown back on and re install the stem back into the movement and test the fit to the case. This might take several adjustments on the tip of the stem to get it fitted properly. Once you are happy with the fit, apply the low hold adhesive to the tip of the stem and screw the crown back on finger tight.
Allow the adhesive to dry for 24 hrs. and you are done.