Tissot Seastar Automatic PR 516 GL

Full service of a classic Rally watch

This is a sad looking Tissot Seastar from 1968. I purchased this watch back in January of this year as it looked like it had some potential for restoration and I could see the previous owner was clearly a “watch guy” as he kept on a Rolex bracelet; I haven’t decided what will become of the Jubilee bracelet yet but for the price, it was a nice toss in.

IMG_2376The watch ran when I received it but it was hard to gauge how well since the crown was missing. I discovered the winding stem was still logged inside the tube though and a bit of digging around in my parts bin uncovered a crown which would fit for testing.

Eager to engage in a more straightforward mechanical watch service after trying my hand at some Accutrons and pin-pallet movements, I popped the caseback off to see what was inside. What a found was a nicely finished Tissot 796 automatic movement which appeared a little grimy but in good shape.

The movement shares the rose gold/copper finish found on most vintage Omega watches
I wonder how Tissot came about selecting such an obscure model number?

Before extracting the movement from the case, I removed the automatic winding rotor. Since the the rotor spins easily on it’s post (for the purpose of winding the mainspring) it’s usually best to remove the rotor first thing as handing the movement with the rotor attached is a bit like holding onto a wet bar of soap.

To this point I’ve only done one full service (breakdown, clean, reassembly) on an automatic movement, thus I’m careful to take many pictures during disassembly to ensure I get each piece back in its proper place!

With the rotor removed the automatic works are visible

One thing to look for when servicing an automatic movement is the amount of wear visible on the rotor edge and inside the caseback. The rotor should spin freely without contacting the caseback or any of the bridges beneath it. A worn bearing will result in excessive play and scuff marks on the caseback or rotor itself. This rotor had a little bit of wear visible on the underside suggesting it may have been coming in contact with the automatic bridge.

Underside of the rotor- note the plating missing from the upper edge

Before removing the automatic works and gear train, the calendar works needed to be broken down. I flipped the movement over and removed the dial to reveal the day and date disks.

The dial is in great condition
The calendar works are hidden beneath the day (of the week) disk

The day disk lifted away easily to review the calendar bridge.

You can see one of the three wire springs ready to give me headaches here

Disassembly of the calendar works of any watch can be a gut wrenching affair. There is usually no less than two springs which are waiting anxiously for the novice watchmaker to liberate them from their prison.  They’ll often take flight, never to be seen again. In this instance I was very careful (and also a bit lucky), the calendar works came away without incident.

I then moved back to the topside of the movement and disassembled the automatic works.

Looks pretty straightforward now

With the automatic works removed, the movement became a recognizable standard Swiss mechanical with the crown and winding wheels on top of the barrel bridge and the gear train beneath.

There were a few surprises be found beneath the barrel bridge however- the first being oil- lots of oil!

Oil has pooled between the bottom plate and barrel bridge here

Before disassembly I had noted that it was impossible to wind the watch using the crown as the watch was stuck in the setting position. Removing the barrel bridge revealed copious amounts of viscous oil pooled around the setting mechanism. I guess the previous owner had issues setting or winding the watch and blasted oil inside through the stem tube. Perhaps he figured after the crown fell off it was the best form of water protection…

The second thing of interest was how Tissot designed the sweep second mechanism as both the forth wheel and sweep second wheel are driven off the escape wheel. The third wheel and second wheel (center wheel) are located beneath a secondary bridge. I’ve not seen a sweep second watch constructed this way before but I like the design.

The wheel for the sweep second hand was hidden beneath the barrel bridge
Beneath this last bridge is the second and third wheels

With the gear train disassembled it was time to finish up with the keyless works. Here is where the only real problem was discovered as the setting lever was badly mangled. This explains why I couldn’t wind the watch.

Bit of grease on the setting mechanism
My old Pontiac didn’t use this much oil
I’ll need to flatten the bends in the setting lever here

The disarticulated movement went off to the cleaning machine and I proceeded to break down the watch case.

The Tissot PR 516 is an interesting beast primarily because of it’s case. Nobody is quite sure why Tissot named the watch 516 but the PR stands for Particularly Rugged or Particularly Robust. The case is milled out of a block of stainless steel and is designed to take a beating. The acrylic crystal is fitted with a tension ring and the caseback is threaded to insure the watertightness expected in a diver’s watch.

I particularly like the crystal design for this model though. The index markers are attached to the tension ring within the crystal.  This creates an additional level of depth as the hands float below the index markers and above the sunburst finished dial. Unfortunately replacement crystals with index markers are not available.

Case broken down for cleaning

I ran the case and caseback through the ultrasonic cleaner and set to work on the crystal with the cordless Dremel and a bit of acrylic polish. The brushed finish of the case was  cleaned up with a Scotch-Brite and the sides were polished back to a mirror finish.

Reassembly was fairly uneventful except for the mainspring which is wound the opposite direction of most Swiss mainsprings. The solution to this problem is just to drop the wound mainspring into a washer which has an inside diameter equal to or slightly smaller than the mainspring barrel, then flip the washer over to drop the mainspring into the barrel. The result will be a mainspring wound the proper direction for the barrel arbor.

Gear train goes back together

Before assembling the setting mechanism, I fixed the damage to the setting lever using a flat stake in my K&D staking kit and a few taps from the jeweler’s hammer. The result was a correctly working setting mechanism.

Reassembled except for the automatic works

A proper sized Tissot crown was sourced from Cousins and I added a new stem to the order just in case.

Cousins had both the stem and a proper Tissot crown
Ready for the dial

Everything had gone swimmingly right up to the point that I tested the calendar setting. For reasons that I’m still trying to understand, the calendar works had seized up resulting in a tooth being knocked off the hour wheel when I turned the hands over midnight. This caused much consternation as the hour wheel for a 796 movement is just about impossible to source. Luckily I was bailed out by OldSwissWatches who had the part in stock. I had to shelve the job for a few weeks while I waited on delivery.

I always save the rotor for last
Rotor is reattached and spinning freely and silently

The end result was a beautifully restored Seastar Automatic.

Honestly I didn’t think it would clean up this nice

The popularity of this timepiece has proved to be lasting as Tissot has recently begun production of the PR 516 once again. The current rendition doesn’t have the floating dial which I think is a nice touch that gives a bit of depth to the piece. This particular one keeps impeccable time and has aged exceptionally well. I couldn’t be happier with the result.

Author: JPMoeller

Amateur watchmaker and California resident

5 thoughts on “Tissot Seastar Automatic PR 516 GL”

  1. Thank you. I have inherited an example of this watch that needs to be restored. I wonder if I can find someone who would do this for me! In any event I learned a lot from your article!


  2. If I remember correctly, the day and date are set by advancing the time to about midnight when the date or day wheel advances, then turning the time back about an hour or two and advancing it again. It will cycle the date wheel, then the day wheel (or the other way around) but not both simultaneously. This allows you to adjust the day and date without turning the hands twenty-four hours for every change.


  3. Thank you for the write up! I’ve got one of these on my bench, and want to ask if the index markers can be separated from the crystal. (I think the crystal on what I’m working on should, ideally, be replaced). Also, how did you get the rotor off? I’m accustomed to rotors that either have a screw in the center, or taking the entire autoworks off as a whole (e.g. Rolex 1530, etc).


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