I just COA'd a 927 I bought for my father. On a fresh wind, it runs at 18000 in positions, as expected... but after a few minutes, it drops to 17980 and settles down... an hour later it is settled out at 17960... and after a few hours drifts all the way down to 17500... where it stays for the rest of the day.

The only other main spring I have is a "good, used spare"... it is a bit better, but still similar in behavior...

I've ordered a new alloy main spring... outside of a fresh main spring... I'm not sure what to look for.

If I give it a couple clicks on the winder, it will speed back up for a bit... but then drifts back down to the lower speed.

The crazy thing is, the watch has above average to great motion on the balance wheel, all the way down... if I have 270 at 18,000... I still have around 200 degrees at 17,500... and the audio is still crisp... the beat error is not affected.

Check to see if the hairspring is snug between the regulator pins.

This main spring had enough power to run the watch, but fell off dramatically over the course of a few hours.

The problem is, that I poised and timed the watch with this spring... a 926 does not have timing screws... so, I had removed two timing washers and under cut two screws to time the watch... then, as the watch ran... it would drop from 18,000 to 17980 to 17950 and on down 'till it settled out around 17500 'till it ran out of reserve...

When I put a new alloy main spring in, it came back to life at 18030bph and stayed there... I had to add timing washers back in to get her to settle out at 18000... she holds 18000 plus or minus 1 beat in any position with the new spring now.

Great dial and hands

Very clean an nicely detailed movement

A lot of us, like mainsprings, get set in our ways, maybe begin to slip a little or sometimes get wound too tight, especially after we have been around for 50 or more years.....

Perhaps that is what is wrong with some of us "oldsters", we need a new mainspring !! I'm sure I qualify and I demand my "senior discount" to boot and I want it now !!!!

Nice looking watch.

regards,
bb

Thank you for the affirmation and the chuckle Buster... Reminds me of going to lunch with my dad... we used to get all philosophical over who was paying... now, I just reach for my wallet.

You wanta go to lunch?