Seth Thomas Electric clock runs slow

[johnboy]

I am repairing a Seth Thomas electric mantle clock model E705-000 with Westminster chime. It has 2 separate spring windings for the strike side and the chime side. The electric motor runs the time side and also winds the 2 springs. After repairing the time & strike movements my problem is that the time side runs slow. It looses about 3-5 minutes a day. I am at a loss as to what the problem is. Any help would be appreciated.
Thanks
Johnboy - a new member to the message board but an old time NAWCC member.

 

[Chris]

John:

Are there any worn bushings on any of the trains? If so, the electric motor may be struggling to overcome this. Check the time train for wear. A pic might help too.

 

[eskmill]

It is likely a problem with the Sangamo motor failing to reach synchronism with the 60Hz (cycles) mains voltage. Of course it also could be caused by a row if missing teeth on the fiber gear.

It could possibly be that the motor is running on its 15 pole "starter" rather than the slightly faster 12 "running poles" for some strange reason.

I'd suggest removing the motor from the movement, then remove the rotor cup and look inside and make certain that the starter rotor (U-shaped magnetic piece) is free to rotate so it can "kick" the bumper pad.

According to Jesse Coleman, the Sangamo motor used on the Seth Thomas movement had some odd characteristics; one being too fast but not slow.

Let us know what you find.

 

[johnboy]

John:

Are there any worn bushings on any of the trains? If so, the electric motor may be struggling to overcome this. Check the time train for wear. A pic might help too.

Chris - Thanks for your reply. The movement has been completely been gone through and repaired for worn bushings. The movement is very free now. Also the fiber gear is in good condition. I am thinking it may be a motor problem.

 

[johnboy]

It is likely a problem with the Sangamo motor failing to reach synchronism with the 60Hz (cycles) mains voltage. Of course it also could be caused by a row if missing teeth on the fiber gear.

It could possibly be that the motor is running on its 15 pole "starter" rather than the slightly faster 12 "running poles" for some strange reason.

I'd suggest removing the motor from the movement, then remove the rotor cup and look inside and make certain that the starter rotor (U-shaped magnetic piece) is free to rotate so it can "kick" the bumper pad.

According to Jesse Coleman, the Sangamo motor used on the Seth Thomas movement had some odd characteristics; one being too fast but not slow.

Let us know what you find.

Thanks for your quick reply. I think the motor in this movement is different than the Sangamo you refer to, but I am no motor expert. There is no separate starter rotor beneath the rotor cup. The motor appears to be the A300-100 that I see in parts catalogs. The motor is clean and runs free. The fiber gear is also in good condition, no teeth missing. The movement has had any worn bushings replaced and the gear trains run free.
Any other suggestions?

 

[stewart]

Hello Johnboy

I've had hands, second or minute rubbing on the crystal, or hitting each other cause electric clocks to run slow.

Stewart

 

[Jeff C]

Hello Johnboy,

I was reading your thread and remember I had one of these, it was in a Seth Thomas Westminster Tambour. On mine the motor was dead actually. I replaced the motor with one that Merritts has, part no. 1556. Its made to replace the A300-100. All I had to do was some adapting to the mounting hardware and it worked well. Its been a few years now without and problems.

Just a thought, good luck with your repair.

 

[eskmill]

Although "The movement has been completely been gone through and repaired for worn bushings." I wonder if Johnboy examined the condition of the two mainsprings?

The spring barrels have no hook so that the outer coil of the spiral spring simply slips in the barrel when fully wound. It is possible that there's not enough "slip." Consequently the spring or springs may be presenting an extra heavy load on the motor causing it to slow except during the quarterly chime and strike phases.

Do this: force the chime and strike trains unlocked so that they run continuously and observe if the clock looses its rate.

 

[johnboy]

Although "The movement has been completely been gone through and repaired for worn bushings." I wonder if Johnboy examined the condition of the two mainsprings?

The spring barrels have no hook so that the outer coil of the spiral spring simply slips in the barrel when fully wound. It is possible that there's not enough "slip." Consequently the spring or springs may be presenting an extra heavy load on the motor causing it to slow except during the quarterly chime and strike phases.

Do this: force the chime and strike trains unlocked so that they run continuously and observe if the clock looses its rate.

Eckmill - At first I didn't understand your suggestion but after looking at the movement again you may be on to something. No, I did not disassemble the 2 mainsprings because they seem to be free and not sticky. Also because the spring housing did not come appart easily. I thought the slip clutch on the spring drive gear would slip when completely wound up but I think I see that is not the case. I tried winding the springs from the back with the small key with the clock. The spring in the strike side seems to slip as you cannot get it to wind tight. The spring in the chime side locks up when I wind it tight. Is this what you were referring to? If so I need to disassemble the chime side spring housing and/or both sides.
Hoping I get your reply.

 

[Richard Haliburton]

A couple of things could be causing the slowness. The motor bearing could be dry or gummy. Another thing that occurs is the breakdown of the grease used in the bearings. The grease works it's way from the hole to the underside of the rim of the rotor. This is another slower upper. These things also occur in United, and Sessions motors.
Some models also had a thrust washer that is often lost when cleaning.
It was placed on the rotor shaft between the rotor and the main body of the motor.
page 419 - 421 of the Best of J.E. Coleman:Clockmaker has an excellent description of the Sessions unit which is similar in design to the motor used in Seth Thomas electric clocks.

 

[Mike Phelan]

It looks as if JB has found the problem. If the chime spring winds up tight, the motor will be running with a heavy load, as per Les' suggestion.
Earlier Smiths movements are like this and have the same problem.

You really need to take the spring out (and the strike one) and clean and lube them.

Just a thought - no half-wit has put a hook in the barrel and a hole in the spring, have they?

 

[johnboy]

Many thanks to everyone for responding to my problem in this thread. All were good suggestions. But the real culprit was the fact that the mainsprings did NOT slip in the spring housings, as first mentioned by Eckmill. I disassembled the springs from the housings, cleaned and relubed the springs. After reassembly the clock is running great and keeping accurate time.
Isn't this message board great?

Johnboy

 

[Tom Kloss]

If either of the two springs in the barrels weren't slipping as they should, wouldn't that eventually cause the clock to stop?

Tom

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