I was curious about my 60r Bunn Specials and fully wound laying on there backs I noted that they ran for 62Hrs 15mins and 62hrs 40Mins, I haven’t replaced the mainsprings myself, seems pretty accurate there 60hr claim. How long would a new spring, cleaned fully serviced watch run for?

Chris,

These are great watches, and what you're finding is part of why we admire them so today. I have not recently timed one precisely, but my experience is the 62 to 64 hour range being common for them. The Sixty-Hour capability is like Elinvar Hairsprings, eventually every watch benefitted from the technology. During the Depression Years of the 1930s they brought everything into fruition and the Great American Railroad Watch reached its peak.

Sounds like you have a couple of good ones, some of them run so well as to be truly amazing!

Lindell

yes, they will run that long, as there are some later 992B movements that had a "54" hour mainspring....

But the main 'point' of the 60 hour mainspring was (IMHO)to:

1. enhance the isochronoism properties of the watch, allowing for 'even' timekeeping ability during various stages of winding
there was an ad in the magazines depecting this feature.. i may have a scan...

and

2. to act as a 'safety cushion' where if a RR worker would forget to wind his watch... the thinking was he may 'forget' one day, but maybe not two....