One of the simplest and most satisfying restorations to a Polerouter can be reuniting it with the correct crown. Though the correct crown for some references can be difficult (and expensive) to obtain, the joy of the hunt and in finally seeing it installed is something any watch collector will understand. The (sometimes) painfully long wait between acquiring the correct parts, and having a watchmaker have enough time to install them for you, is also something most collectors will also understand…
Fortunately, crown and stem replacements on Polerouters are a straightforward, simple job, and one that most collectors should be able to manage at home. Below is a simple pictorial guide on how to do it yourself, using just a few simple tools.
Remove the caseback by unscrewing it anti-clockwise. In all seriousness, this is likely the hardest part of the procedure, and can prove to be a bottleneck if the case has been overtightened, has been reinstalled without the correct o-ring or gasket, there is corrosion, or all of the above.
In my amateur experience, the best tool is an original UG caseback tool (if you are lucky enough to find one), but there are also a number of aftermarket modern options for generic caseback removal tools. I recommend at least a 3-prong caseback tool for polerouter casebacks, as 2-prong tools are prone to slip and either scratch the caseback or round the caseback edges.
Remove the old crown/stem. Firstly, be sure to pull the crown and stem all the way out into the time setting position. This is very important, as if the stem is released whilst in the winding position, you will need to remove the hands and dial to reset the whole mechanism.
Once in the time setting position, the stem release can be pushed in whilst pulling the crown out. Do not apply too much force on the crown, as once released it will almost fall out on its own. Now you have your stem and crown separated from your case/movement.
Unscrew the crown from the stem. The original style of stem and crowns were threaded and screwed on together. So, you should be able to remove the crown from the stem by gripping the squared part of the stem with pliers, and unscrewing (anticlockwise) with your fingers, or another tool if needed.
Take care not to use too much force, and risk snapping the stem. Also be aware of the possibility that the combination has been (incorrectly) glued in the past, so both a new stem and crown may be necessary if they cannot be separated or the thread on the stem has been damaged.
Install the new stem and crown combination. Steps 3 and 4 will vary slightly depending on what is being used/reused from the old combination. The original stem and crown combination does not need to be glued, and can be done in the reverse order of the description in Step 3. Simply hold the squared part of the stem with some pliers, and twist the crown on clockwise as tight as possible with your finger grip only.
The stem will need to be the correct length, both so that it can fully engage the mechanism, and that there is no gap between the crown and case. There are probably more precise methods out there, but personally I use trial and error, whilst erring on the side of caution.
I first fit the stem and crown as is to the movement and case, then measure the gap between the crown and case, and cut the stem incrementally, test-fitting again each time, until the stem is the correct length.
Install the stem/crown into the watch.This is simply reinserting the stem and crown into the mechanism. Unlike in the removal step, the crown release does not need to be pushed to reinstall it.
Test the time setting function and winding functions operate smoothly, and that the stem is locked into the movement. If it goes the whole way in but can be removed again without pressing the stem release, then you probably forgot to remove it whilst in the time setting position (Step 2). If so, the dial will need to come off to reset the mechanism… a nuisance, but not the end of the world.
Reinstall the caseback. Take care not to overtighten it, check there is a gasket/o-ring – If not then add one before reinstallation.