Synchronome No4 Turret slave stopped!

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After a series of snowfalls and sub zero temperatures overnight I noticed the hands on the 30" dial on the shed gable end had stopped.

This is the first occasion such an event had occurred. It had run for years safely protected from the elements. So I am presuming the minute shaft had frozen a little creeping moisture inside the hour pipe. The No4 is a heavy duty slave movement with twin electromagnets and double locking on the impulse mechanism to stop the hands from slipping under wind or ice loads.

Rattling the armature of the slave made no difference. The hands still refused to move. So I climbed a ladder and gave the hand boss area a spray with bicycle chain lubricant. This is a light mixture of penetrating oil and a lubricant. This did not have an immediate affect but later I noticed the clock was gaining on its foolishly early morning time which had shown earlier.

Once the sun had fallen on the dial there were no further problems that day. I advanced the hands to time on the slave movement and then left it to run. Depressing the armature overcomes the double locking impulse mechanism. Allowing the impulse wheel to be turned forwards by hand. Turning the clock backwards is not possible.

I shall have to monitor the dial to see whether yet more frost will bring it to another standstill.

Turret slave dials used to have a poor reputation for reliability. This may simply have been caused by moisture running down the hands to freeze in the hour pipe. There is no reserve of energy to move the hands beyond the normal return spring. This offers a degree of safety since no energy is consumed trying to work against a blockage in the mechanism.

The hands stopped again overnight but restarted on their own. Leaving the hands at completely the wrong time! So I ran some light 'cycle' oil into the hour pipe this time. Just to see if that helps and then reset it to time. A clock dial showing the wrong time is far worse than one set to 12 o'clock and deliberately stopped. Mains synchronous clocks used to to be non-self starting in case they fooled the owner after a stoppage. Better to see the hands have stopped to prove the wrong time is being shown.

The clock stopped a couple of times more after snow and overnight frost. Reinforcing the theory of ice being trapped between the minute arbor and the hour pipe. I applied yet more oil and slave worked again despite -7C overnight frosts. Even more oddly, the dial gained the 20 minutes it had lost and continues to show the correct time after two days. Well, that saved me getting the ladder out again but makes absolutely no sense.  

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