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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    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.
     
  15. Dan_in_WA

    Dan_in_WA Registered User

    Dec 21, 2019
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    7E253D38-A97C-490F-A2B2-53FFDE5EF476.jpeg
    I pulled the bushings out of the Sessions clock motor I’ve been tinkering with for awhile. It had badly worn bushings, so it was already junk.

    I think focusrsh_b07732 has the answer as far as putting bushings in the original bushings. I’ve looked on the ‘net and can’t find any bronze bushings that are anywhere close to what came out of this motor.

    The picture above is the front bearing, a non-magnetic spacer (aluminum?) and the rear bearing.

    The only other answer I can see would be to carve new bushings out of blank stock, and that’s probably beyond what most of us can do, myself included.

    I took careful measurements of everything with a dial caliper, if anyone is interested I’ll clean up my sketches and post them here.

    Kudos to you focusrsh_b07732, I think you gave us our answer!

    Edit: Would a reamer give a good enough finish after the new bushings were installed?
     
  16. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Dec 17, 2009
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    "Edit: Would a reamer give a good enough finish after the new bushings were installed?"

    I was taught that after using a broach or a reamer, you have to follow up with a smooth broach, which is essentially a tapered burnisher. Put a little oil on it and give it a few twirls.

    Regarding the bushings: I made mine out of standard brass round stock, but now that I've had more experience with these clocks, I think making them from Oilite or something similar would be better.
    The constant issue I keep facing is that the motor is running at a few hundred RPM, which is 100X what is inside any mechanical clock, and the bearing have to be designed to handle that.
     
  17. focusrsh_b07732

    focusrsh_b07732 Registered User
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    Dec 17, 2009
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    This is a follow-up to my previous postings about bushing the Sessions motor. My advice was WRONG!
    It turns out that brass bushing just don't have the lubrication ability necessary to run for any length of time in these motors. The couple of hundred RPM of the motor is 1000x what a brass bushing in a normal clock experiences, and they will run out of oil. I found this out when a few weeks after rebuilding two Sessions motors with brass bushings, they started making noise.
    The correct solution is to completely drive out the Oilite bushings in the motor and replace them.
    The motor has two bushings of the same diameter but oddly, of different thicknesses. I bought a piece of .500 x 3" Oilite rod from MSC Industrial, part # 61223988 ($7.01), and turned it to .0409 diameter. The rotor shaft is .069", which doesn't match any wire drill size I have, so I used a .067 drill (#51) and then used a tapered ream and a smoothing broach to open the bushing ID to the right size. A person could also make a two-fluted drill bit from a piece of #50 drill blank (.070) ground down to size.
    The trick is to install the bearings so the bores align. A spare rotor arbor will help while you press in the bearings.
    The two clocks are now running happily and most importantly, quietly.

    IMG_6935.JPG
     
  18. Rockin Ronnie

    Rockin Ronnie Registered User
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    Nov 18, 2012
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    This is good to know. It is no wonder they are typically tossed out when they stop running.
    Ron
     
  19. Dan_in_WA

    Dan_in_WA Registered User

    Dec 21, 2019
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    I looked up MSC # 61223988 and it came up as 3/8” dia.

    Do you have a link or p/n? 1/2” x 3” didn’t come up in my search, but then I’m doing this late at night...

    Thanks, Dan
     

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