Expert: Kenneth Saunders - 11/25/2008

Question
I recently purchased a 9 chime tubular grandfather clock at an estate.  The maker of the cabinet is unknown but the movement is a Hermle 1171-850.  The back plate is marked 87 1171-850 94cm.  My question is this, I have attempted to set the clock time but the clock still runs excessively slow (2 minutes an hour).  The pendulum is adjusted upward as far as it will go.  The pendulum length appears to be approximately 44 inches with a 10 1/2" diameter bob.  Both the weight shells and pendulum bob are very ornately inscribed and appear to be a set.  From what I can tell from research I have done is that this may be the pendulum for this movement but was made for a 114cm 1171-850  movement.  Possibly the previous owner replaced the weight shells and pendulum as a set to dress up his clock and purchased the set but got the wrong pendulum length?

Currently, I am trying to determine the correct pendulum length for this movement.  I have substituted a shorter length pendulum to try to determine the real pendulum length for this movement.  But the one I am using has a smaller diameter bob as well.  Will the diameter of the bob affect the  swing of the pendulum as well as the the length?  If I shorten the current pendulum at the attachment of the pendulum to the suspension leader will I have to also take into consideration the larger diameter pendulum as well as the length?  I read that Hermle made this movement with three different pendulum lengths so would replacing the escapement wheel be the best over all repair?  Also how can I determine the correct pendulum length for the current clock gearing?  

My goal is to minimize any further expense as replacing the pendulum would be very expensive when trying to match the weight shells and clock face.  I would like to try to use the pendulum and weight shells that are currently on the clock.  I am a clock hobbyist and my time is cheaper then most parts!  I do have the ability to perform most any corrections that could be recommended.  Any other recommendations would be most graciously appreciated.
Thank you

Answer
dia. of bob will not effect swing much at all- length will.


no real change in timing using a 8.5" dia disk, but smaller than that yes it will run faster slightly.

to get a 94cm pendulum out of your 114cm  you need to make it
7 3/8" shorter(in theory)

the pendulum leaders that join the suspension spring and the pendulum top come in two lengths if they are brass 5.5" and 4 3/8"
if they are chrome- come 2" to 6 7/8" long. so you can shorten some here or cut the leader and overlap solder it shorter yourself and do the same with the pendulum top to get the length you need. These joints do not show when in the clock.

You can fashion a hook out of a paperclip that will allow you to hook the top of the pendulum further up the leader, or drill some small holes in each so they can overlap higher and get pinned with a piece of wire and then wrapped the rest of the wire around the joint to temporarily test the speed effect of shortening the assembly.

as to escape wheel changes -NO- Hermle changes the gear on the rear of the handshaft inside the back plate to change pendulum lengths--and you do NOT want to get into that.