Repairing and Adjusting a Rolex 1210 Oyster Speedking 6420 Precision Wristwatch

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The natural habitat for broken and abused watches is eBay. A recent fishing expedition in eBay’s murkier waters yielded this old Rolex: an Oyster Speedking 6420 with the 1210 hand-wound movement.

Here’s what arrived in the mail. As the seller noted, the stem doesn’t stay in the case.

The screw-down crown has failed in two ways. The inner threads are stripped, and the spring-loaded sleeve has split.

The case shows signs of being manhandled. The gouges on the back come from some unknown but incredibly inept person who tried to open the screw-down back without the right tool. These oyster cases get sealed so tight that it is futile to open them without a milled-to-fit Rolex die.

Otherwise, the stainless steel case shows only the usual scuffs and swirls of use.

The case has the usual crud and grime that comes with years of use without being cleaned.

The crystal is a lost cause. You can’t buff away the crazing fractures in the plastic.

The dial looks great: nicely toned and definitely original. It goes into the dial vault for safekeeping.

Cleaning the Movement

The movement was gross and crusty inside. I suppose that’s what happens when your screw-down crown fails. There’s grease and grime and more rust than you ever want to see on a watch.

The watch got the usual cleaning, but several pieces were set aside for additional hand cleaning. There were a lot of rusty screws.

Oddly, the watch was missing a dial screw. That’s never a good sign—it means that at one point the watch was serviced by someone who lost it and then said, “Well, whatever.”

Finding a genuine replacement screw for this old caliber proved nearly impossible, at least at a price that normal humans wouldn’t find shocking. Fortunately, my assortment of tiny dial screws had a few that fit.

Adjusting the Movement

As always, it’s best to start adjusting by taking stock of the watch to see what kind of accuracy standard to aim for.

For this 1210, there are some good signs. It’s a Rolex, after all, and this watch is in good shape. But there are bad signs, too. This watch has been neglected, and not all Rolexes were engineered for fine timekeeping.

The world of Rolex has its own lingo: words like oyster and perpetual and precision have their own quirky meaning. Only in Rolex World does putting PRECISION on a dial mean that the watch is actually less precise than your typical watch. The “Precision” grade movements weren’t COSC certified, but they are fine movements.

You can see an accuracy compromise in the balance wheel, which isn’t ideal for fine-tuning. There are two mean-time screws that can be turned, but the rest are flat-faced with no screwdriver slots. Some of the flat screws show some high-quality but deep dimpling.

This will make adjusting irksome. Those flat-faced screws aren’t easily removed, so I’ll probably have to hold this watch to lower accuracy standards. A Hamilton watch from the same era, in contrast, would have removable screws that would make adjusting much easier.

After cleaning, oiling, demagnetizing, and a few days to settle down, the watch was ready for adjusting.

At first, the watch had terrible amplitude.  As we’ve seen in other posts, persistent low amplitude is a global symptom with many, many causes. I could rule out some obvious ones, such as an old mainspring or a balance wheel way out of beat. And I had tested the freedom of the mainspring barrel around the arbor, and nothing seemed to be binding against the bridges. Hmm….

After much consternation and staring, I figured it out. Someone had spread the banking pins. On this movement, the pins are fixed. But at one point, someone bent them lightly to widen them. Madness, I say. On a modern movement like this, you essentially never need to “set up” an escapement like this. You see banking-pin shenanigans on old pocket watches all the time, but I wasn’t expecting it here.

Once the pins were straightened, the watch perked up and had great amplitude in all 6 positions. And the rates were dead steady, as one would expect from a Rolex. Here are the watch’s initial rates. (For people new to the blog, note that we’re staring at the movement from the movement side, so left and right are reversed. See here for a background.)

That’s not bad. The dial up (DU) and dial down (DD) positions are reasonably close, and most of the other 4 positions are fairly close as well.

The biggest flaw is that the pendant down (PD) position is around 30 seconds slower than the DU/DD positions. When a wristwatch is adjusted to 3 positions, the DU, DD, and PD positions are aligned. So if we had to pick on of the vertical positions to be close to DU/DD, we would pick the pendant-down one.

It’s possible I can slow the movement down and improve its poise just by tweaking the mean time screws. Here’s the movement oriented pendant up.

The mean-time screw falls exactly on the vertical line of the stem and crown. This isn’t a coincidence. Adjusting one mean-time screw more than the other can shift the wheel’s poise to favor the PU or PD position. Because adding or removing weight would be irksome with this watch, I’ll simply adjust it to 3 positions (DU, DD, PD) by shifting the mean-time screws.

While doing this, I could see that the screws were already unequal. One was nearly all the way in, and other was mostly out. This suggests a big poise error in the balance wheel somewhere.

After a couple rounds of rotating the two screws, here are our final rates.

The 3 positions are pretty good: the pendant down position sits evenly between the dial-up and dial-down ones.

Frequent readers of this blog will think, “Hey, this could be better.” When you look at the 4 vertical rates, you can tell that there’s a heavy spot in there. But for this watch, I’ll go against my perfectionist instincts and leave it alone rather than tinker with a balance wheel that wasn’t designed for it.

Repairing & Restoring the Case

For automatic watches, screw-down crowns don’t cause quite so much wear-and-tear. But for hand-wound watches, the crown’s threads and tube’s threads have their daily grind, so either the tube or crown will fail eventually.

The Rolex’s case tube had a hole worn through it.

Genuine Rolex parts are hard for a humble hobbyist like me to get, so it is off to the aftermarket. For these older Rolex models, you’ll find different kinds of case tubes, and not all will fit.

The case tube is rotated in and out using a case wrench with a splined tip. Some tubes have the splines deep in the tube, like the one in the center.

Others have wider splines at the opening and a smooth inner tube, like the one on the right.

With a new vintage Rolex crown, a new tube, and new gaskets all around, the movement should stay clean and tight.

Polishing the Case

Although some corners of the Internet find polishing old watches to be sacrilege, it’s my watch, not the Internet’s, and I think this old case could use some freshening up.

To start, the case back is slightly domed. The bulge makes a straight, linear grain challenging to achieve. The grain would bulge around the dome, making it look odd. Before polishing, the back showed the usual signs of age plus some gouges from a tool slipping.

The first step is to mirror polish the back to a striking shine. When doing so, you need to take care to avoid polishing the case edges or threads. This piece turned out unusually well.

The bezel was mirror polished, too. The goal wasn’t to grind out all the nicks and scratches but to simply bring back the bling to this high-quality stainless steel.

Once the back was shiny, I applied a circular finish using Garryflex abrasive blocks. A slick, mirror polished case back gets sticky during warm weather, which is why case backs are usually brushed. It turned out great, if I do say so myself.

For the case itself, the polishing was light to avoid rounding the lug edges. I mirror polished the sides using the polishing lathe and applied a brushed finish by hand with an abrasive block to the tops of the lugs. You can still see some nicks and scuffs: better to leave them than deform this small case.

Wrapping It Up

With a new crystal, this watch is ready for wear. I think I’ll keep this one for a while instead of releasing it back into the stream of eBay.

These small, hand-wound Rolexes have a lot of charm and wear nicely.

But I’m not sure if the screw-down crown is a design triumph or a design flaw for a hand-wound, non-automatic watch like this. It keeps the case tight, but opening the crown to wind it daily means that the crown, tube, or both will have a short life.