Advice on selecting PA type waterproof replacement crystals

[MyFavoriteObsession]

Hello again. I've recently had to replace PA type crystals for the first few times and have found it confusing, which is not surprising in itself, as I often find getting out of bed confusing. In the past, I've measured the outer diameter of a PA crystal, made a best effort to match it to one in the GS catalog and ordered a replacement, only to consistently receive a crystal that is too small (both times with Wyler watches). Am I missing something? For example, I have a 1961 Bulova Sea King that I like very much, but that needs a new crystal. The outer diameter is 28.3mm. In the GS catalog, they offer a 28.3mm crystal for a Bulova, crystal PA 437. Could anyone please tell me if there is a factor I'm not considering when selecting PA type replacement crystals? Thank you!

[watchweasol]

Hi  The general convention was to add 0.01 to the measure ment.  I suggest you have a look at the Esslinger web site  and watch their tutorial  for fitting crystals, It contains a lot of useful information, better than I could explain.                              

[MrRoundel]

That looks like it might be the type of case that the forties and fifties Perregaux Sea Hawks used, as well as a few others. If so, they can be a bear to find crystals for.

I have had success using a GS crystal for a Wyler on a tough-fit Perregaux. And I am still searching for the right one for a GP Amphibian. I've tried two or three "almosts", but it's still waiting for the right one to come along, so to speak.

The problem with this type of case is that the crystal must not only snug firmly against the case back. It must also allow the bezel to cinch the outside of the crystal and hold the bezel to the back through that fit. In other words, it has two critical measurements. Unless the GS, or other, brand crystal specifies the watch model, it's tough. Again though, I'm speculating that this is the waterproof type of case that GP, Wyler, Benrus, and a few others used. If not...never mind. Good luck.

[rodabod]

On 6/15/2020 at 7:37 PM, watchweasol said:

Hi  The general convention was to add 0.01 to the measure ment.  I suggest you have a look at the Esslinger web site  and watch their tutorial  for fitting crystals, It contains a lot of useful information, better than I could explain.                              

I presume you mean centimetres! It’s usually 0.1 or 0.2mm larger diameter. 
 

MFO - in short, measuring crystals is worthwhile but not reliable as some older types shrink, and they compress under the caliper jaws. 
 

What WW describes is the best way to do it as far as I’m aware - measure the rebate and then select the next size up to provide an interference fit. 

[MyFavoriteObsession]

Mr. Roundel, you have the exact idea. The crystal must fit over the bezel, rather than inside it. I'm fairly comfortable selecting the correct size high dome acrylic, but these PA waterproof type crystals are another matter entirely. To clarify, this type of crystal can be pressed on by hand and doesn't require a crystal lift. It's not a PHD or Stella High Dome type. 

For example, I have a Wyler with a bumper automatic movement. I can't find the model name, so I went by the original crystal size: 27.2mm outer diameter. The GS catalog had one for a Wyler "1073" that was 27.2mm, model PA385-25, so I ordered one (at a cost of around $15.00). When it arrived, it measured 27.0mm actual outer diameter, thus too small. So, I moved on to the next Wyler crystal that was nearest in size, a 27.55mm for a Wyler "1085", model PA403-20. This crystal actually fit over the bezel, BUT the outer ring will not fit over the outside of the new crystal! I'd also ordered yet another crystal for a different Wyler (it too was the wrong size, of course), so by then I was out nearly $50.00 with only one (barely) fitted crystal. That's when I thought it best to ask here before I have more crystals than Waterford. 

The Wyler in question:

 

[MrRoundel]

Well, like MyFavoriteObsession, I am now about $50 into crystals that didn't fit. Unfortunately, it doesn't seem to be likely that I'd find a GS crystal that specifies the GP case that it is for. Yes, I occasionally see them so labeled, but not for the watches I have.

Oh, and on the GP case, it is the bezel, incorporated with the lugs, that must fit over the crystal. So while there are similarities in design between the GP and Wyler waterproof cases of the period, there are also important differences. I just tried a GS PA 360 25.9mm that was marked for a "Harvel" watch. It fits PERFECTLY over the case back. Unfortunately, it seems to be ever-so-slightly too thin to hold let the bezel hold well to the lower assembly (Case back and crystal.). I think I am going to end up shimming it somehow, or even placing a few spots of glue somewhere at the join between the crystal and bezel.

One little additional tidbit, the PA 360 that is designated for the Harvel has two different envelope markings that are .1mm apart. Some are marked 25.9mm, which is the one I have now, and some are marked 26.0mm. I don't know what GS's thinking is on this. Actual different sizes? Or was it a correction of an earlier erroneous measurement? Or perhaps newer PA 360's are made larger so they will work as they need to on my Amphibian? Tough to say unless I now go into the $60 into crystal place.

I really like this watch so it's frustrating the heck out of me. Fortunately I have enough heck in me to hold out a while longer. Cheers all.