Trouble with Sessions Motor

Discussion in 'Electric Horology' started by Bates, Feb 8, 2020.

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  1. Bates

    Bates Registered User

    Feb 6, 2013
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    Can anyone tell me why this sessions motor is making this noise? It only makes the noise when turned a certain way. It seems that the noise is coming from the rotor touching the main part of the motor because it’s not straight but I can’t figure out how to straighten it if that’s even the real problem. Any help would be appreciated.





    thank you
     
  2. Karl Thies

    Karl Thies Registered User
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    Mar 13, 2018
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    First, the rotor has a distinct wobble and that might cause it to clip the base. Second, the small tension washer might be missing. Third, The bushings for the rotor might be worn oblong. Or a combination of all three.
     
  3. Bates

    Bates Registered User

    Feb 6, 2013
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    Karl,

    Where does the tension washer go?
     
  4. Karl Thies

    Karl Thies Registered User
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    Mar 13, 2018
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    Tension washer in on the pinion between the rotor and the coil base.
     
  5. davefr

    davefr Registered User
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    Nov 29, 2008
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    Semi Retired Engr. Mgr - Currently Rebuilding Tele
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    Do you feel any slop in the bushings? Any detectable movement side to side means the bushing is worn and will need to be replaced.

    If the bushing feels good then try to balance the flywheel so it's not wobbling. If you have to disassemble it, punch the shaft thru the flywheel vs the pinion gear.

    That motor probably has two bushings with a oil reservoir or oil wick between them. Replace, clean, re-lubricate as appropriate.
     
  6. Bates

    Bates Registered User

    Feb 6, 2013
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    I don’t fell much bushing wear at all. I’ve attached a video in which I hope to show the wear. Maybe it’s too much? The other side has less wear.

    I think the problem is in balancing the flywheel. I don’t know how to do that. I’ve tried to look for places that may be out of round, but I don’t see any. I’ve attached a photo of the flywheel as well.



    33217FDF-2FC3-4908-ACC2-6CC527F52CB2.jpeg
     
  7. davefr

    davefr Registered User
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    Nov 29, 2008
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    Upon inspection, do you see any signs of metal to metal contact on the underside of the flywheel or the main body of the motor?

    That amount of play on the top bushing looks suspect. Especially if it's more pronounced then the bottom. If you can feel any slop, it's probably too much wear.

    I have a bunch of those motors. I could probably pick out a good one if you can't fix yours. Just send me a PM.
     
  8. Bates

    Bates Registered User

    Feb 6, 2013
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    Problem solved. In examining the flywheel very closely, I noticed a small amount of play in the bushing on the flywheel. This bushing is staked onto the flywheel. I restaked it and now the extreme wobble is gone and the motor makes no noise in any position in which I hold it other than the normal hum.

    Thank you for your help
     
  9. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Dec 17, 2009
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    By an amazing coincidence, I started working this morning on a Sessions electric banjo clock with exactly this problem, and the FIRST discussion is see is about it!
    Anyway, I measure .110 inch "endplay", for lack of a better word, between the worm gear and the bushing. That is, the arbor can slide in and out that much. Is that correct?

    Sessions endplay.JPG
     
  10. davefr

    davefr Registered User
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    Nov 29, 2008
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    Yes, these motors have a lot of end play. The clock movement centers the pinion gear to where it needs to be.
     
  11. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Dec 17, 2009
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    For the past couple of days I've been trying to get the Sessions motor to run silently. Although I could detect no slop in the central brass bushing in the coil, I found that after putting a thick clock grease on the rotor shaft and the bushings, the clock ran silently for an hour. But after it heated up and the grease thinned out, it started making noise again. That convinced me that the bushings were worn. So I rebushed the central bushing in the coil on both ends and now it is running quietly.
    Apparently, these motors can tolerate zero play in the bushing. I think that is because it is turning so fast, any out-of-balance or wobble on the rotor causes it to shake and make noise.

    rebush coil 1600.JPG
     
  12. Rockin Ronnie

    Rockin Ronnie Registered User
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    Nov 18, 2012
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    Do you have a photo of the new bushing and its placement on the motor?
    Ron
     
  13. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Dec 17, 2009
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    That is what you are looking at in the above photo. Look again at the photo and you'll see a shiny brass bushing pressed into a dark surround brass (bronze) part. It is a BB-36 brass bushing, 1.5mm H x 3.5mm OD x 1.4mm ID. I put the bushing in a lathe and gradually opened up the ID to .067" (#51 drill). A broaching tool was then placed in the tailstock and, turning the lathe by hand, I opened up the bore so it was a snug fit on the rotor shaft. This was done for two bushings.

    Each end of the brass inner part of the coil, which was the original bearing surface, was then drilled out to .136" (#29 drill), using progressive larger drill starting with a #50 so as not to risk changing the hole center. I drilled the hole just deep enough to accept the 1.5mm H bushing. Then each bushing was pressed in, and again broached the tiniest amount to restore the ID diameter so it fit over the rotor shaft. Finally, each bushing received a pass with a smoothing broach.

    Very straight-forward work, just like bushing any clock.
     
  14. Rockin Ronnie

    Rockin Ronnie Registered User
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    Nov 18, 2012
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    Thanks, I should have looked closer. It is good to know that wear in these motors can be addressed.
     

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