bellmatic problematic.

[notenoughwrists]

I've a Seiko Bellmatic (17j Japan 4006 - 6020) that I've had serviced recently and is running well, but it makes a funny noise. It initially sounds like the rotor is grazing the case at one point as it rotates, as theres sort of a hit or click per rotation but I've opened it up and tht's not the case.

Does anyone know what happens when the watch is fully wound? Does some sort of clutch kick in to let the rotor spin but not transfer that wind through to the mainspring?

I think that this clutch thing (if i'm right - you've probably guessed i'm not overly technical :lol: ) where it stops one of the winding cogs is the source of the noise. I can get a piccie of where I think the issue is, if anyone knows anyhting about these movements....


The curved arrow shows direction of wind, the straight is some sort of bar that stops it unwinding (?). anyway, this cogged wheel seems to turn clockwise when winding, then when fully wound, turn a little (but not one whole cog tooth), make this click, and not advance any more - and the same thing once or twice per rotation of the rotor.
I'm purely guessing, but I think this is when the mainspring is fully wound. When not fully wound, it winds normally, holds a good charge, and timekeeping is spot on - but this bloody noise when it's on your wrist and fully wound sounds like the movement is falling around inside the case. V. Annoying.
(and I can't send it back to the repairers, as they've closed down!

[clockworks]

All automatics have a slipping "clutch" to prevent overwinding the mainspring or damaging the winding mechanism. Usually this is in the form of a slipping bridle inside the spring barrel. The inner end of the spring is attached to the winding arbor (central shaft that the gear you indicate is fixed to), but the outer end locates on a piece of spring that's a sliding fit inside the barrel. When the spring is unwound, the outer coils push the bridle onto the barrel wall, where it grips. The spring can be wound by the rotor.
As the spring approaches full wind, the coils move into the centre of the barrel, releasing pressure on the bridle, which can now slip on the barrel wall. The inner end of the spring still gets wound, but the outer end unwinds.

Whether Seiko autos work the same way, or if the "magic lever" of the winding mechanism slips instead, I've no idea. Keen to find out, though. Your description suggests that the "magic lever" slips.

[notenoughwrists]

Cheers - I can sort of comprehend the mechanics from your description, very much appreciated.
There's no chance I'll be pulling it apart (well not if I want it to work again!) but i'll keep on with trying to find if the clutch should make that much noise, and if I find out any more details on how it does work, i'll give you a shout.

Rob

[dickbrowne]

The principle of the Seiko auto winding clutch is pretty much the same as most others - the mainspring will slip when it gets to a certain pressure.

The "bar" you indicate is indeed the part of the mechanism which stops the mainspring unwinding.

Underneath the rotor (the weight which winds the watch) is a "bridge" - it's just a piece of metal which cogs and stuff sandwich between, underneath this is a mechanism called a pawl, more commonly known as a "magic claw" or "magic lever" which engages one side or another of a cog, depending on which way the rotor is turning - take a look at http://horologyzone.com/watch/watch-sch ... drive.html for a good illustration, the pic you want is about halfway down. Your watch isn't a spring drive, but the relevant pieces are similar, and it's a good way to visualise what's happening when your watch is self-winding.

It is probably this lever engaging and disengaging that you are able to hear. You can check if it's the mainspring slipping which is making the noise - take a jewellers screwdriver, and turn the screw in the middle of the cogs you are indicating in your picture clockwise (As if tightening it up). This will tension the mainspring, and the tension will be held in place by the ratchet. If the mainspring is causing your noise, you will hear it whilst turning the screw. If it doesn't make the noise, turn the weight, through about half a turn, then back a few times. If the noise is present, try turning the rotor one way only for a couple of turns. If the noise disappears, then it's the magic claw engaging or disengaging, if it's still there then it's something between the auto wind mechanism and the mainspring.

Hope this helps

Richard

[Nick Evans]

I have a few Bell matics and they wind nice and smoothly. You can get a mechanical noise a bit like a rattle or a clunk if you wear it with the alarm fully unwound. The little hammer inside the case that makes the alarm noise is fairly free to wobble back and fore if the alarm spring is fully unwound.
When I wear mine I usually give the alarm a half dozen winds just to quiet it down a bit.

[notenoughwrists]

dickbrowne - Thanks for all that, i'll run through a few tests and try not to knack anyhting up!!!

Nick Evans - Mine does wind beautifully, and keeps excellent time. If I was deaf, i'd never have thought there was an issue. (there may still not be, could be my oversensitivity!) and good point about the alarm wind, i'll check the bell hammer thing, but I think it's not that....

I'll let you know what I find.
Cheers chaps

Rob