Hamilton 950b winding

[Robert T. Raucher]

Hi...what would cause a Hamilton 950b (double roller) to run for only 8 hours and then have to be rewound because it had "rundown"? It seems to rewind fully. Prior to this it was always good for 24 hours or more on each rewind. Rewind stem does NOT appear to "slip" when winding. Can a Mainspring "break" and still funtion partially? How does that happen? Or is there somewhere else I should be looking?Thanks. Robert Chico, Calif.

[Robert T. Raucher]

Hi...what would cause a Hamilton 950b (double roller) to run for only 8 hours and then have to be rewound because it had "rundown"? It seems to rewind fully. Prior to this it was always good for 24 hours or more on each rewind. Rewind stem does NOT appear to "slip" when winding. Can a Mainspring "break" and still funtion partially? How does that happen? Or is there somewhere else I should be looking?Thanks. Robert Chico, Calif.

[Robert T. Raucher]

Hi Doug. I do NOT "count" the turns to wind. I wind till it stops winding (tightens up tight). However...I THINK I am now winding LESS turns..to get to a tight wind. Any more thoughts? Robert.

[Tom Huber]

How about the wrong mainspring? One that is about 2" too long. Tom

[mikeh]

Robert,

Do I understand correctly, that it used to run 24 hours, and that it has not been worked on since that time?

Is it keeping time OK?

If it is keeping reasonable time, I don't see how it could be anything other than the mainspring. I'd probably just try and replace it and see what happens.

Regards,
Mike

[Steven Mercer]

Tom

This might be an awful newbie question but I have to ask.

How does a longer mainspring make a watch run for a shorter time?

Steve

[Kent]

Steve:

It takes up more space in the barrel so that there's not enough room for the spring to expand as it unwinds. Hence, the spring stops delivering power sooner.

Kent

[Steven Mercer]

Kent

Thanks.

Steve

[jagkar]

Dear Robert,

Please advise how you are deciding that the watch is "rundown," that is are you determining that in fact there is negligible driving force exerted by the mainspring or is it only that the train is not powering the escapement? If the latter, probable cause is broken jewel or severe lubricant failure. Pardon me if this already crossed your mind, never hurts to ask, eh?

[Robert T. Raucher]

Thanks for all the input. I think it may be the Mainspring. I noticed tonight when it ran down..and I went to rewind it..the winding crown "slipped" and I wound it a few turns from the beginning again..and again I felt a "slip". It has NOT beeen worked on recently and when it is running it is keeping good time. Robert Chico, Calif.

[Robert T. Raucher]

Doug. You are correct. I agree. I became of change in the winding process a little after that email. Robert

[Lindell V. Riddle]

Robert,

You are getting sound advice from very knowledgeable people, but problems in interpretation can develop when something like this is diagnosed with written correspondence, rather than "hands on" examination or even over the phone. In reading the early part of this discussion I agreed with the others that your problem sounded very much like a broken mainspring. Especially the fact it only recently will not fully wind and you felt no slippage. But now you say...

"the winding crown 'slipped' and I wound it a few turns from the beginning again..and again I felt a 'slip'."
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I'm going to make a suggestion, it may or may not help, but you may want to at least eliminate this potential problem. Could it be the click spring? If the little spring mounted behind the click is fatigued, misaligned or broken it could easily cause the situation you are now describing.

To be sure, carefully remove the case back. Hold the movement in your left hand, with the crown at the top. At about the 11:00 position, you'll see a crescent shaped device known as the "click" which is so named for the sound it makes as you wind the watch. Holding the watch in your left hand slowly move the crown back and forth. You should see the teeth on the click positively engage the teeth on the winding wheel allowing it to move forward, but not allowing it to rotate backwards.

If on the other hand you see the click is not always fully engaging or only intermittently engaging and then releasing, which would then allow the winding wheel to "slip" back, you have found the basis of your problem. My reason to suggest this is the turn your explanation has taken, along with the fact we should always eliminate every possibility, and perhaps we should also try to eliminate the simpler and easier to repair items first.

Your problem may in the end turn out to be a failed mainspring, but on the other hand you may find the exercise described above helpful in determining exactly what has happened.

We're all interested in how this turns out!


Lindell