Expert: Kenneth Saunders - 7/22/2008

Question
Thx for answering my previous question.  I have another.  I have two mantel clocks (Sessions & Junghans pendulum movements). I've cleaned both clocks and installed new mainsprings.  Timekeeping seems to be erratic - it appears that the clocks run fast when spring is freshly wound then slow down as mainspring uncoils.  May lose a few minutes in a week.  Are mainsprings too strong?  I thought I selected the same spring size, etc.  How common is this problem?  Thanks for your time.

Answer
common to all spring driven clocks- this is why weight driven clocks keep better time- and the shorter the pendulum, the more sensitive to the changes in power of springs.

You can try not winding fully to see if you get a better weekly run.

new springs tend to be stronger even than the new original springs were, due to advances in metalurgy.