Seth Thomas 120L Movement Problem

Discussion in 'Clock Repair' started by Jeffrey Smith, Oct 12, 2018.

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  1. Jeffrey Smith

    Jeffrey Smith Registered User
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    I'm hopeful fellow members can help me with a problem. I purchased this mantel clock with an ST 120L movement. After installing a new mainspring (with the original specs), cleaning and oiling, I started it up on my test stand and noticed it would run only 9 hours before stopping even with a full wind. Restarting it several times (without rewinding) it would run anywhere from 4 hours to 45 minutes before stopping repeatedly. There was no consistency or pattern in where the clock would stop. My first thought was there was some drag in the time train.
    I completely disassembled the movement, inspected all pivots and holes but could not find anything obvious. Much against my better judgement, I installed a slightly stronger mainspring, and reassembled and oiled the movement, pallets and cams. I restarted it on the test stand and it ran for over 6 days before stopping. Restarting it (again not rewinding) it ran for another 29 hours before stopping. Further restarts cause the clock to go only for minutes now. But the mainspring still has a fair bit of tension on it when testing it with a key.
    I am convinced there is some undue source of drag in the gear train, as the originally specified mainspring should be able to keep the clock going. As a side note, the strike side works perfectly.
    I have heard these are finicky movements from other postings I've seen here. I'm looking for any input, or similar experiences, and of course any suggestions on what the problem might be. Again, I lean toward a bent pivot pin or something.

    IMG_2183.JPG IMG_2184.JPG
     
  2. R&A

    R&A Registered User

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    #2 R&A, Oct 12, 2018
    Last edited: Oct 12, 2018
    How worn are the barrels? And did you peg all the holes? Holes still look a little dirty:???: You can take the power down and check the barrel for wear.
     
  3. bruce linde

    bruce linde Technical Admin
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    i'm not familiar with that movement, but had the following thoughts after reading your post:

    - curious about your cleaning process... and how do you clean pivot holes and pivots? do you burnish the pivots?

    - do you have a lathe or other method for spinning arbors and making sure pivots are true?

    - do you polish pallet surfaces (and how)? add a hint of oil to them upon reassembly?

    - any chance the crutch is loose on the pallet arbor?

    - are those 'before' pictures? do you have an ultrasonic?
     
  4. shutterbug

    shutterbug Moderator
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    Memory says there should be washers under the bottom plate on the front. Is there?
     
  5. R. Croswell

    R. Croswell Registered User

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    I believe the 120 bottom plate mounts over the edge of the upper plate without requiring a washer but there may be variations that do.

    Springs are usually not the problem. With no history, I would look first to the escapement. I believe this one has a deadbeat escapement. Make sure the escape wheel teeth are landing on the dead face of each pallet. If the EW teeth are landing on the impulse face or on the division between impulse and locking faces this one will not run. Once you confirm that the escapement is operating properly when the crutch is moved by hand, hang the pendulum and make sure the clock is "in beat". Let us know what you find.

    RC
     
  6. Jeffrey Smith

    Jeffrey Smith Registered User
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    Thank you all for your input, they are very welcome. Let me answer all your questions in order:
    I cleaned the movement several weeks ago with both a brush to remove the dried oils, and in an ultrasonic bath. I only inspected the barrels and all pins in the time train visually for scoring. Those that looked a little suspect, I burnished by hand with scotchbrite. The holes look clean, but I did not peg them, my thought was the ultrasonic cleaning would remove any fine dirt.
    I don't have a lathe to spin the arbors to see if they're running true, I probably could do that while the movement is assembled if I remove the springs and verge, and check with a dial indicator.
    I did put a small amount of oil on the pallets, but I did not polish them. The entire assembly is tight on the crutch.
    The pictures I included are after I changed the mainspring and started my tests.
    I checked the single spacer on the center post (it acts as a shim to make up for the thickness of the bottom plate that holds the barrels), and it is in place. However, I will check to make sure the bottom plate is not warped and is parallel to the front plate. I will also check the escapement as suggested by Shutterbug. The clock is in beat, and I started a second test and the clock has been running for 40 hours with no hiccups.
    Thanks again for all your input! I'll update with any new information I find. In the meantime, if any other thoughts come to mind, please let me know.
     
  7. kinsler33

    kinsler33 Registered User

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    It's not clear if you disassembled the movement or not. If you can't, take the barrels off and run the rest of the movement through the ultrasonic cleaner again (I use 30 minutes, with heat in a straight solution of Zep Fast 505 de-greaser.) Then lubricate the movement and see if that improves things. My guess is that it will not, which means that the movement must be disassembled and each pivot inspected, polished, and blessed by an ordained priest. Then assemble each train by itself in the plates and see how loose the pivots are. Install the appropriate bushings, checking each wheel for bent pivots by installing it in its newly-bushed holes and seeing if it's free to rotate.

    Put it back together, check the escapement, and see if that helps.

    M Kinsler
     
  8. Jeffrey Smith

    Jeffrey Smith Registered User
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    I finally did disassemble the movement last week (forgot to mention that) and burnished the pins for any that looked suspect. All holes looked to be clean, and there were no sloppy, worn pivots. I reassembled the movement and restarted it Friday afternoon.
    Yesterday, after reading M. Kinsler's suggestion, I stopped the test and used a dial indicator to measure any runout while manually sequencing the crutch. I left the main spring in place to apply power to the timing train, and to put a load on all the shafts. I found the escape wheel shaft to be running out about 0.0025" All the other shafts seem to run true. What is an acceptable amount of runout?
    I restarted the movement yesterday afternoon and it is still running this morning. Once again, thanks to all for your suggestions!
     
  9. R. Croswell

    R. Croswell Registered User

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    In this case, it is the amount of run out of the escape wheel itself that's important. You can't rally put a dial indicator on the EW teeth, but if you let down the main spring and remove the verge and just a enough hand power to make the EW spin you should be able to visually detect any significant runout of the EW. If the EW is running true at the teeth don't worry about the arbor (shaft). If not, and if you have a lathe, you may be able to take a light cut off the pivots to bring them true but that will require bushing the pivot holes. In a given clock one would expect the EW to run as true or more true that the other wheels.

    RC
     
  10. kinsler33

    kinsler33 Registered User

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    A small runout of the escape wheel won't stop the clock, and yours is small. But when I'm really stuck with a clock that won't keep running and the rest of the time train seems fine, I'll generally take another look at the pivots of the escape wheel and of the verge. Most trains will run fine with pivots that rattle a lot, but any lost motion in the escapement pivots makes a large difference in the performance of the clock. So I will generally bush these pivots, leaving just enough side-shake to ensure easy running, but no more than that.

    If you don't have one, it's not a bad idea to think about this tool, which I suspect everyone has, and uses, but won't admit it: Behold:

    Plate Spreader

    You first let down the mainsprings. Then you loosen or remove the nearest plate screws or nuts. Then you apply the jaws to the plate edges and turn the lousy little knurled screw so that the jaws spread the plates apart. Don't worry: the plates spring right back without any problem, and while they are spread apart you can fish out, say, the escape wheel and find a pair of close-fitting bushings to fit its pivots. Other wheels may fall out while you're doing this, but not many. Then once the wheels are all back in place you can turn the knurled screw to let the plates back together again. I won't tell.

    M Kinsler
     
  11. R. Croswell

    R. Croswell Registered User

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    I don't have one, don't want one, and wouldn't use one if I did have one. Got to completely separate the plates to install the bushing anyway so what's the point?

    RC
     
  12. kinsler33

    kinsler33 Registered User

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    Once the escape wheel is out you let the plates spring back together, tighten the appropriate plate screws, ream the pivot holes, and poke in the bushings from the inside or the outside, whichever is easier (usually the outside, in this case.) Check the clearances of the bushings with the escape wheel pivots from the outside of the plates, spread the plates again, and install the escape wheel. It's handier if you've got the verge out or otherwise pushed aside, for then you can check the freedom of the train.

    I've found that it's generally unnecessary to file out escapement pivot holes in an attempt at preserving tooth depth because the escape wheel and verge holes always seem to wear fairly round, which to me indicates that they tend to bounce around in every direction.

    This treatment--and it's far easier to do it prior to assembling the clock--seems to perk up many troublesome movements.

    Mark Kinsler
     
  13. Bruce Alexander

    Bruce Alexander Registered User
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    Is there any significant looseness in the regulation/chops assembly?

    ST 120.jpg
    P.S. Please ignore the 3rd arrow near the middle of the movement.
     
  14. kinsler33

    kinsler33 Registered User

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    That's quite important, and I'd suggest that you look at that prior to doing any other remedy. It's a source of lost motion in the escapement and can make a very large difference in the performance, and I should have suggested it myself.
     
  15. bkerr

    bkerr Registered User
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    So I know this sounds really stupid but is it possible that it is slightly out of beat?
     
  16. shutterbug

    shutterbug Moderator
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    I do have a plate spreader, and do occasionally have use for it ... however I don't think I'd want little brass filings finding their way into the wheels of an assembled movement. In my humble opinion, bushings should always be pushed in from the inside of the plate, which makes disassembly mandatory. It would be best to catch sloppy escape wheel holes before final assembly. I do understand that there are many ways to skin a cat, however ;)
     
  17. R. Croswell

    R. Croswell Registered User

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    That's my feeling as well, plus I can't recall ever servicing a clock that required bushings at just one arbor that didn't have several other pivot holes that also be bushed. Attempting to install bushings this way (#12) would seem to preclude the use of a bushing machine and demand that the holes be reamed by hand which usually requires that the bushing be peened, soldered, or glued to secure it, especially if pressed from the outside. Then there is the unknown condition of the rest of the pivots which cannot be evaluated without separating plates. Yes.......there are many ways to skin a cat. (I doubt that the cat would approve of any of them).

    RC
     
  18. Jeffrey Smith

    Jeffrey Smith Registered User
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    Thanks again for all your suggestions. I did check the fit of the suspension spring in the chops, and there was no slop. So far the clock is running well, though now I have a problem with the gathering pallet and getting the number of strikes correct. I just submitted another posting about that issue. As for the timing side, I believe there were several problems that all came together to cause the short run time.
     
  19. kinsler33

    kinsler33 Registered User

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    I've never used or even examined a bushing machine, but you can place an entire movement on the drill press table and the reamed holes will be nicely perpendicular. Why would a bushing that's pressed into a cylindrical hole from the outside of the movement have to be peened, soldered, or glued? My KWM bushing reamers do not seem to produce a tapered hole even when rotated by hand or with a power screwdriver (which works better.)

    M Kinsler
     
  20. shutterbug

    shutterbug Moderator
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    When you insert a bushing into a proper hole (parallel sides), the bushing compresses as it is inserted. That causes the first part that is inserted to be more compressed than the trailing edge. That in turn makes it harder to push the bushing out from the "back" side. So if you insert from the front, the bushing will be more easily pushed out through the front side than from the back. During normal operation, you can lose a bushing and cause a fatal crash.
     
  21. kinsler33

    kinsler33 Registered User

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    Why would the insertion of the bushing render a cylindrical hole into a tapered one?

    M Kinsler
     
  22. Uhralt

    Uhralt Registered User
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    I think you misunderstood what SB said. The bushing itself is compressed and becomes slightly tapered, not the hole in the plate for the bushing.

    Uhralt
     
  23. Willie X

    Willie X Registered User

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    When you have a dependable run of several days before stopping, the problem can be just about anywhere BUT more often than not it's in the escapement, pallet arbor, crutch to leader eye, reason of the clock.

    With the pallets removed, will the time train run with 2 or 3 clicks of tension on the spring? If yes, stop and release the E-wheel with your finger repeatedly and see what happens. Then turn the movement 90 degrees, with the plates in plane with the floor and see how that goes.

    It's best to do this with just the time train assembled. Test run it that way too.

    Willie X
     
  24. kinsler33

    kinsler33 Registered User

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    One other hint from the battlefield: if the movement is running--say on the test stand--give the whole thing a twist both ways and in both planes. A slightly bent or tight pivot will stop it dead.

    Mark Kinsler
     
  25. breeze

    breeze Registered User

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    As the plate spreader has been brought up and commented on I thought I would comment as well. The end not used for spreading plates is V shaped and is used to spin suspect arbors to check or confirm bent arbors or pivots. I do not remember ever using this tool for spreading plates ( nor do I think I ever would) I do sometimes use it to check for bent arbors. You know now that I think about it I know I said I would never never use it to spread plates but.. I do have arthritis in both my hands so someday I may have no other option.

    breeze
     
  26. Bruce Alexander

    Bruce Alexander Registered User
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    In my opinion and in my hands the Plate Spreader is a good tool to have if it used with caution and common sense. I find it most helpful when making minor adjustments to upper gear timing in the strike and/or chime trains.
     
  27. shutterbug

    shutterbug Moderator
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    It's also handy for count wheel stop pin adjustments.
     
  28. kinsler33

    kinsler33 Registered User

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    I was having a rough time assembling grandfather clock movements. Going from the chain wheels toward the top, I'd always have trouble with chime and strike fans and their drive wheels falling out, or having their pivots bent, or in a couple of cases their pivots broken, eek. So I started leaving those parts out until the clock was completely assembled and then using the plate spreader to insert them between the plates. Practice has improved matters a bit, so I don't always need the plate spreader these days, but it's a very handy tool to have.

    The only caution to be observed when using a plate spreader on a spring-powered movement is that you absolutely have to make sure that all mainsprings are let down, even if you're sure that, say, the time train won't be affected when you adjust something in the strike train. I believe I still bear a scar in which you can see the tooth profile of an Ingraham great wheel.

    M Kinsler
     
  29. bangster

    bangster Moderator
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    What Shut said!:)
     
  30. Bruce Alexander

    Bruce Alexander Registered User
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    That's kind of what I was saying. Lock Pin placement, Warning Pin runs. Timing of the Strike and Chime Trains can be more easily adjusted using a Plate Spreader because it allows you to precisely split and hold the plates just enough to free and adjust the gears in a train from the top down, usually one at a time. As a novice, you just have to be careful not to bend a plate. They can also come in handy when trying to split plates which have a lot of rust or corrosion.
     

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