Weak hammer stroke

Posted: Thu Dec 08, 2011 3:50 pm     Post subject: Weak hammer stroke

I have a 341-020 mechanical work. I replaced the mainspring in one barrel (slightly thinner spring) and the time was slow so I exchanged the barrel with the one for the hours. The barrels are #40. The time is no longer slow now but most times you can't hear the hammers hit on the hour. I thought it was because the mainspring in that barrel was slightly smaller so I recently replaced that barrel with the same size and number from another clock and it still does the same thing. Why are my hammer strokes so weak?