After many years of pocket watch fascination I acquired a Seth-Thomas Plymouth mantel clock. It was given to me by my sister who knew about my fascination with watches. I cleaned and oiled it and it ran fine and chimed after adjustments were made. I found another one that was similar on e-bay and cleaned oiled and adjusted it and it ran and chimed just fine. Lately after winding them they both gain an hour on the chimes. After synchronizing the chimes they are fine until I wind them again. Then they become unsynchronized again. I am sure it is a common problem since both clocks do it but I am not sure what causes it. Any help will be greatly appreciated.

Hello David,
I had the same issue recently with a newly acquired ST mantel clock. What I found to be the cause for the problem was that when winding the strike ('chime') mainspring, the bulk of the spring would tend to "migrate" or "climb" up and around the winding arbor somewhat unevenly while the key was actively under tension until it was wound fairly tight, and this was causing the edge of the mainspring to brush and slightly move the count wheel (which is held in place only by side tension). (as well as bumping into some delicately "tuned" levers) The "fix" was simply unloading the mainspring so it could get a fresh coating of heavy spring lube, fully winding/releasing a few times to be sure it was evenly coated, and then the spring quit climbing and jumping while being wound, staying more "concentric" to the arbor and thus stopped altering position of the count wheel.

Hope this helps- David

Thanks, David. That explains what my 8 day Seth Thomas is doing too, though instead of being a Westminister, it's a hour/half hour that tends to jump 30 minutes and chime the hour ON the half hour....then the half hour on the hour.

After resetting several times, over a couple day period, it finally straightens up.

Doesn't do it all the time, but the spring definitely 'jumps' when wound, so it appears the spring needs some grease.

Regards! Mark

Good information David,
I recently worked on a clock that had springs that were binding. (You could hear it occasionally break loose inside the barrel). And it ran very slow.
I cleaned and lubed the springs and now it runs considerably faster.

All the above is generally due to the springs need to be removed and cleaned and then lubed with good clock spring lube. Which means they need to be removed and that is another job. It is like adding fresh oil to your engines dirty oil if they aren't removed.