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Sessions Pendulum Issue

JHPez

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May 12, 2010
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Hello I have a sessions Mission clock which you can barely tell that the pendulum is moving (the pendulum hangs on outside of clock). The clock does keep time within a few minutes, however is it normal that the pendulum barely moves? Could the clock have the wrong pendulum? or? Any help would be appreciated!
 

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Bruce Alexander

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How long has it been since your clock was serviced? It sounds like it might have an issue with the escapement. Perhaps pallets in need of adjustment or badly worn.
You state the the pendulum barely moves. Can you provide a measurement of the pendulum arc?
 

shutterbug

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Welcome, Joseph! Interesting thing about your pictures. I was going to rotate them for you, but when I click on them twice, they orient themselves correctly :)
Those are usually very strong running movements with lots of pendulum travel. I suspect that the clock has not been serviced in a long time, and needs some professional help. The pendulum is not the issue.
 

lpbp

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I agree it needs service, about the only thing that can cause that issue is incorrect depthing on the verge.
 

Rob P.

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Dec 19, 2011
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Pendulum weight is not the issue. Someone here on the forum recently did a pendulum weight "test" where they swapped pendulums for different weighted ones and the test movement ran fine. I also know this to be true for a fact because I have a pair of Sessions mantle clocks. One runs with a no-name pendulum on it that is much lighter than the factory one and that particular clock runs as accurately as the matching Sessions mantle. Same movement, same vintage, same, same, same. Just very different pendulum weight. And the timekeeping is just as accurate.

Therefore, if your clock has an anemic swing, it problem lies elsewhere. Most Sessions movements, of the type you pictured, are recoil escapements. Recoil escapements need as much engagement depth (lock depth) as possible and still allow the escapement to function. This depth is controlled by moving the anchor arbor closer to the escape wheel.

To do this on your clock, you need to move the "dog bone shaped arms" that the anchor arbor is held in. Move them closer to the escape wheel increase the lock depth.

A TINY TINY TINY amount is all you need to move them and be careful to not pry on ANY arbor shaft to move them because you can break or bend something. Move them in until the escape wheel won't release and then move them out until it does and a whisker more for extra clearance. Check by sighting along the shaft that it is parallel with the other shafts. If not, adjust until is it parallel and as deep as it can go while allowing the escape wheel to move.

All of this assumes that the rest of the movement is in good shape and not in need of a major overhaul. If the movement is grungy you should consider a full service teardown and do the adjustments as it is reassembled if the adjustment is necessary (it may not be needed once the clock is fully serviced).
 

Willie X

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Feb 9, 2008
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These clocks wear out at the top. Take the movement out and check for wear. There is a good chance that you will find severe wear at both ends of the escape wheel arbor and the pinion ends of the two arbors before the escape wheel. The pallet faces wear out too. It would normally have a pendulum swing of about 1 inch.

Willie X
 

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