Hour Wheel Ring Purpose

[RickTock]

Greetings!

I'm in the process of servicing a ladies Seiko 1520B movement. While removing and sorting parts from one of my cleaning baskets, I discovered a 'new' part I didn't recall putting in the basket. This part was not documented in my disassembly photos. Hmm.

I found an inventory list for the 1520 and reconciled my parts collection to the list. What I found was something called an 'hour wheel ring' on the parts list that sounded like a reasonable description for my new found part. I'm guessing it was stuck to the hour wheel when it went into the cleaning basket and found its freedom through the spa treatment.

But to be honest, I wasn't even sure what an hour wheel ring does or where it goes. I don't have a schematic diagram for the 1520, so I looked for another Seiko movement that had an hour wheel ring in its parts list and found the quartz 775x series included such a ring. And I found a schematic for the 775x (see excerpt below). So now I know where the ring goes, but I still have no idea why it's there. Other than serving as a very very thin spacer, what is the purpose of an hour wheel ring?

Thanks!

Edited November 7, 2023 by RickTock