The Croydon utilized the 8/0 sized 748 movement with 18 jewels. The sterling silver dial featured luminous applied dots, markers and numerals with lumed hands to match.
I recently had an opportunity to overhaul a Croydon so I can show you what makes it tick... literally.
As received, the watch was in pretty good shape, consistent with a 60 year old watch. A quick pass on the buffing wheel cleaned up the crystal nicely.
The two-piece case is normally sealed by a gasket. This one has been lost to time but still closes firmly. Like most CLD's, the Croydon has a two-piece stem with the female portion attached to the crown and the male portion inside the movement.
The 748 movement (and 735 / 736) is probably one of the most challenging movements to reassemble - but I'll get to that after I take it apart. Here you can see it was pretty dirty. This much dust can make a watch run sluggish - if it runs at all.
With the hands removed the two dial foot screws are loosened so I can remove the dial.
This dial doesn't have any markings on the back - which leads me to believe it is an original dial.
The front of the main plate is pretty dirty too - and matches the back. You can see the hour wheel and cannon pinion in the center of the movement - these have to be removed to take the back apart.
Unlike most movements, the first thing to come off is the train bridge - it's holding four wheels. But first, the tension has to be let off the mainspring. The mainspring can store a lot of potential energy and it needs to be released or parts can be damaged when the train bridge is removed.
The 748 is interesting in how the motion is transmitted to the second hand. On earlier movements (the 987S) the second hand is a pinion (small wheel). On the 748 the second hand has a large wheel (center) and it's driven by the fourth wheel. The fourth wheel actually has two wheels, one for the second hand wheel and one for the escape wheel.
Confusing, isn't it? Try putting one back together!
All four wheels are removed to expose the Barrel Bridge with the center wheel underneath. Early 748's had a one-piece barrel bridge, making it a real pain to change the mainspring as the entire train assembly had to be removed to get access to the mainspring. This movement is a later 748 design with a two-piece barrel bridge - so a portion of it can be removed to get access to the mainspring barrel without taking the rest of the movement apart.
Here you can see the first portion removed - exposing the mainspring barrel. If the train bridge was still installed I could still remove the mainspring barrel.
And now the center wheel is exposed.
With everything removed but the balance assembly - that comes out next.
Under the balance assembly is the pallet fork - which is held in place by it's own bridge.
Here's a slightly out of focus shot of the pallet fork. It's very small and easily lost so great care is taken when handling it. You can see the two ruby pallet jewels.
WIth everything off the backside, the main plate is flipped over and everything comes off the front too.
With all the parts in the cleaner, the case is washed and cleaned up as well.
The mainspring is cleaned and reinstalled with fresh grease.
Everything is dried and ready to be put back together.
First the pallet fork goes back in. It's a little hard to see in the lower left of the movement.
Getting the pallet fork arbor lined up properly is critical. If it's not lined up just right, when you tighten the bridge screws you'll hear "pop" - and that's the end of your pallet fork. Here you can see it's a little out of alignment as the bridge isn't laying flat.
With the pallet fork installed, the barrel and the center wheel go back in.
And their bridges are installed.
Now comes the hardest part. All four wheels have to be lined up at the same time so the train bridge can be reinstalled. When I first started messing with watches I made the mistake of taking a 748 apart. I tried for about an hour to get it back together before finally breaking one of the pivots when I thought (in frustration) that it was "close enough". There is no such thing as "close enough" in watch repair... it's either perfect or it's wrong.
In this shot you can see the two wheels that make up the fourth wheel. The silver one on top drives the second hand. Under the silver one is a pinion driven by the third wheel (left) and the gold wheel at the bottom drives the escape wheel (right).
The trick to getting everything lined up is to look at it from this angle (which would be looking at it from the right side in the photo above).
Now, with all the bridges reinstalled and some tension applied to the mainspring, the balance is oiled and ready to go back on.
With the watch running, it's flipped over and the keyless works is reinstalled and lubed.
The set lever bridge is reinstalled and everything is ready for the cannon pinion (for the minute hand), hour wheel (for the hour hand) and the dial to go back on.
Inside the case, the female portion of the stem is turned so it can accept the male portion when the movement goes back in.
And finally, with the dial and hands back on the "case is closed" and this Croydon is ready for some wrist time. Although, maybe I'll try my luck with re-luming, these hands are looking a little naked now.
And just for thoroughness, here's a wrist shot of my black dialed Croydon. I guess I'll relume these hands too when I do the ones above.