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Seth Thomas 77A movement

gentleman jim

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Dec 7, 2008
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Just received this clock. During my pre-tear down checks i noted it is missing an arbor and lever. Arbor located at the top right from the back of the clock. It looks like the lever was intended to engage the large wheel on the winding arbor. The clock runs well without it. Does the missing arbor/lever have any critical purpose?


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dickstorer

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You are missing the pawl for the maintaining works. It keeps power on to the escape wheel while you are winding the clock. It is not necessary to keep the clock running. I will post a picture in the morning.
 

Willie X

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Feb 9, 2008
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Yes,

The missing part is the maintaining power pawl and arbor. It is part of a simple mechanism that keeps power applied to the train while the clock is being wound. Without it, the delicate dead beat pallets and escape-wheel can be damaged.

Temporarily, you can use slight finger pressure against the minute hand, in the clockwise direction, while winding. This will also maintain the power to the escape wheel. Watch the second hand, it needs to keep stepping foward in the normal manner, while the clock is being wound.

Willie X
 

brian fisher

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Yes,

The missing part is the maintaining power pawl and arbor. It is part of a simple mechanism that keeps power applied to the train while the clock is being wound. Without it, the delicate dead beat pallets and escape-wheel can be damaged.

Temporarily, you can use slight finger pressure against the minute hand, in the clockwise direction, while winding. This will also maintain the power to the escape wheel. Watch the second hand, it needs to keep stepping foward in the normal manner, while the clock is being wound.

Willie X
I'm pretty sure this is out of a Seth Thomas #2. the idea you have of keeping pressure is a really good one, but unfortunately it is impossible with the face installed on this clock.
 

bruce linde

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willie said you could keep gentle forward pressure on the minute hand... but i’m curious about the ‘could damage pallets or escape wheel’ part.

i would think this part would be easy enough to make if one had a lathe... i wonder if it’s the same part in both the 61a and 77 movements?
 

Willie X

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AFAIK, the only purpose for maintaining power is keeping the heavy pendulum from wrecking the escapement when an escape-wheel tooth goes point to point.
Willie X
 

dickstorer

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I am not the expert, but I believe the internal parts are the same for the 77B and the 61A. The motion works is different. It could be out of a ST #2 or several other ST wall timepieces. Almost any ST wall, one weight timepiece, with a 80 beat movement used this movement.
 

bruce linde

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AFAIK, the only purpose for maintaining power is keeping the heavy pendulum from wrecking the escapement when an escape-wheel tooth goes point to point.
Willie X

i had never heard that... i thought the sole purpose was to provide power to the clock while winding... since the winding temporarily engages the pull of the weight... hence the name 'maintaining power'.

in another thread ( #16 ) burkhard says he was told damage could occur if the pendulum stopped swinging ... but the pendulum keeps swinging and the movements keep ticking on all of my weight-driven regulators with maintaining power when i'm winding them... because of the maintaining power. without the maintaining power wouldn't the impulse faces still keep the escape wheel turning while winding?

as far as i can tell from what i've read, damage can occur with bolt-and-shutter maintaining power (i.e., in turret clocks)... but i've found no mention of same for spring-driven harrison-type maintaining power such as in the ST #2.
 

Willie X

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Yes, it is there to retain power during winding. But, the reason is to prevent point to point damage in the escapement.

Ever heard a Hershede go point to point? It's not something you want to hear!

WIllie
 

shutterbug

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If I were running without the maintenance lever, I believe I'd stop the pendulum before winding. You won't lose that much time, and it might prevent wheel damage.
 

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