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Cyma Watersport with R.420 bumper movement - what an adventure!

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Hi all, hope all is well.

Here is a little write-up with photos of my latest adventure in watchmaking as a beginner.

This is the 5th watch I've worked on and I decided to step up from the base manual wind to an automatic movement. This one just happened to be a bumper movement.

I think I likely overpaid for this watch given its condition ($100 CDN) but I was excited at time time to find it. I did not notice when buying it had a bent lug - I posted in the past here on how to possibly straighten this. The case is also quite beat up. which seems fairly common in my overall price range. I enjoy the wear and patina on the dial though and once polished it still looks good I think.

Here are the before:








You can see that the metal bracelet that must have been stock to the watch has really worn into the lugs. More on that later. This watch certainly seems like it earned its keep for its original owner(s). I've no idea how that deep groove formed on the non-crown side, near the bottom of the case.

My first stop after un-casing was attempting to bend the horn back. I didn't want to go through the service if I was to just end up breaking the horn off of the case. I did not have an appetite to send this out to a professional for a real (expensive) fix with laser welding, etc. I don't know what this case is coated with, there are no markings for gold anywhere on it. Using gold as a guideline though, I looked up its melting temperature vs. the annealing temperature of brass. Brass can be annealed at a much lower temperature than gold melts, per google, so out to the garage I went. I used a small torch to apply heat to the bent horn and then careful crushed the horn in a vise (with jaw protectors) to attempt straightening. Heat, crush, repeat. I tried to be very careful. While not a 100% perfect result, it is much better than before. I probably got it about 85-90% good, I think. I chalked this up as a success and I was now able to move to the movement.

While not really a real walkthrough, I am including the breakdown of the movement here in case it helps someone in the future. Just looks nice as well, I think. My process is to take a photos basically after removing every component, as my guide to putting back together. I had to start disassembly with the movement in the case as I could not get the crown and stem out. It also did not turn. It turned out that the part whose name I can't recall right now (on a pivot and sits in stem) was out of place and binding things up.














Some notes about the servicing - this movement is the one I posted about as to how to remove that wheel that was pressed on (drives the seconds pinion). At first I ended up using the bridge underneath to pop it off. The method that ended up working best, having to add/remove the wheel I few times, was to hold the wheel underneath still while rotating this pressed on wheel, and it would rotate up and off. Thanks to another forum member for that tip.

I also want to note what a pleasure it was to take out the balance jewels with the type of shock protection (cymaflex?) they had. I am sure it isn't the best and is from when different mfg's were trying different things, but on the balance side it was as simple as moving that arm over, and the dial side removing the screw and taking off that C shaped spring. Even more pleasant than incabloc, I thought!

This mainspring was the smallest I have dealt with yet. I don't have mainspring winders but came up with a method of using two pegwoods to wind the spring back in, after I initially got it started with my fingers.

I am not recalling anything else interesting about the taking apart of the movement at this time.

edit - added this in after reviewing before hitting post - I noted the worn lugs up top from the original metal bracelet. What I ended up doing was filling the wear areas with jb-weld. You cannot notice it when the strap is on. I used the kwik-set version, which sets up in 6 minutes, vs. the very long set time of the original formula. It was very nice to apply actually, with a toothpick. I was poking at it too quickly, I think, after my first attempt and it all peeled fell off. It was still in a bendy state when I was checking adhesion. For my second attempt I sanded with 800 grid where I was going to apply, and then didn't touch it until the following day. Though the set time is quick, cure time is still 4-6 hours. So far so good, I think, time will tell how it stands up. The area around one spring bar hole especially needed something, I thought. This was the best solution I could come up with.

Cleaning up the case after putting the movement back together, I found a flat plastic gasket on the case back that I had not previously seen. Was in fine condition once removed. Upon re-casing everything, I found that when I screwed the case back on, it must have been impacting with the stem as I could not wind or move the crown into time setting position. I posted another thread here asking if anyone had any input on if this style of watch had a rubber gasket to go with the plastic one (thinking the rubber one may have just dried up and been removed in the past by someone curious). No one replied to that thread, but, with this my only idea on how to keep the back from screwing on so far, I ordered a bag of rubber gaskets from amazon and added it in. It seems like a success, as far as I can tell.

I also had some issues when re-casing with the crown. There must be a rubber gasket in there that dried up but I could not see for sure. The crown was extremely hard to turn and move in and out. After different attempts at lubricating (silicon, molykote dx grease, vaseline [maybe not the best option]) it moves nicely enough now. I am still getting used to the noise and feeling when manually winding an automatic, since the gear ratio on the automatic weight is so great.

In my endeavors to keep costs down I sanded the crystal through successive grits, finally polishing with autosol as I have it on hand. There are two minor cracks I did not see when the crystal was all scratched up but they are at the edges and not noticeable unless you are looking for them. I was worried about the crystal shattering when pressing back in with my diy setup but was lucky. Though a crystal is about $10 CDN for me, I am not within driving distance of the supplier and shipping is at least $15.

Finally, the end result:





On the timegrapher I got good results in flat positions, face up and down, but performance suffered when the case was once its side, if that makes sense. I don't know what that means or how I could improve that, but as long as the watch keeps good time for a day I am happy as I change my watch every day.

My next watch to work on is an Orient of unknown age - it is a manual-wind but will be the 1st watch I work on with a date complication.

Take care all.

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3 hours ago, Charette said:





On the timegrapher I got good results in flat positions, face up and down, but performance suffered when the case was once its side, if that makes sense. I don't know what that means or how I could improve that, but as long as the watch keeps good time for a day I am happy as I change my watch every 

In vertical positions, more surface area of the pivots rid on the jewels,therefore more friction and lower amplitude.

Adjustments to decrease positional variations start with that of the end shake on balance staff, furthure adjustments is generally made if the watch is a good grade one and by experienced watchmakers. 

Show us the difference in amplitude to see of it is acceptable.


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On 1/16/2023 at 2:42 AM, Nucejoe said:

In vertical positions, more surface area of the pivots rid on the jewels,therefore more friction and lower amplitude.

Adjustments to decrease positional variations start with that of the end shake on balance staff, furthure adjustments is generally made if the watch is a good grade one and by experienced watchmakers. 

Show us the difference in amplitude to see of it is acceptable.


Thanks for your response. Here are some photos of readings in different positions. I focused on the screen but you can still see the watch position in the foreground. I adjusted things when assembling when the movement was flat and get good results here. I did not know how to adjust for beat error on this movement.

I am quite happy actually that none of the positions lose more than a minute. Today is the first full day I have worn the watch and I can’t see it losing sun time so far. Maybe my wrist is mostly flat during the day (I do work at a desk/computer).










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