Seems I broke my Juki-LS-341, again... (Bobbin Shuttle)

[Yoshi888]

Hey everyone,

I love my Juki-341N, but it seems I once again managed to damage my poor machine.

I was sewing as usual, but suddenly it bunched up. I removed my work piece and the thread, but also with the handwheel, it was not properly turning anymore.
So I started disassembling it to see if there was some thread stuck near the bobbin, but there wasn't anything. 
Then I removed the whole shuttle to see if there was anything wrong.

I have attached a video here, and it seems the bushing inside the brass/copper ring gets stuck when I turn the handwheel too fast.
I have cleaned everything I can, and I cannot find anything stuck anywhere.

If I slightly push on the Bushing, it seems to work better, but also after cleaning and reattaching the bobbin, it gets stuck very easily.
I did not want to disassemble it more because I am not too knowledgeable about this, and I am worried about ruining the alignment/timing.

Do you have any idea what could have happened here and how I could fix it?

In case it is relevant, I changed the shuttle a few months ago, but there have not been any problems since then.

[friquant]

Take a look underneath at the hook driving shaft. Check if the bevel gear on the (horizontal) hook driving shaft is snugged up against the bevel gear on the (vertical) hook shaft. If there is a wide gap between the two bevel gears, I could imagine it binding up.

Also verify:

• No missing teeth on either of those two gears.
• Three set screws tight on bevel gear on (horizontal) hook shaft
• Set screws tight on feed dog vertical movement eccentric (mounted on horizontal hook driving shaft).
• No interference between feed dog vertical movement eccentric and either of the bevel gears

[Yoshi888]

Thank you so much for the advice

I took a look at the gears, and there are no teeth missing. It appears that the vertical driving shaft has some play, but I think that might be because it is fixed to the center screen on the Bobbin Carriage (Sorry, I sometimes don't know the proper part names yet.)

I cleaned any dirt on the bevel gears, but that did not change anything.
 

I'll take another closer look tomorrow, but if I cannot find anything else, I will probably start removing the other parts to take a closer look at the vertical shaft.
Is it possible to disassemble it further without ruining the needle/hook timing?

[friquant]

32 minutes ago, Yoshi888 said:

Is it possible to disassemble it further without ruining the needle/hook timing?

@Yoshi888 Can you turn the machine slowly by hand and identify what/how it is actually binding? 

The situation I suspect the most is that the set screws that hold the bevel gear in place (and keeps the correct timing) are loose, and the bevel gear has moved laterally away from the other bevel gear a little bit. The way to check would be to loosen the three set screws in the bevel gear and press lightly to slide the bevel gear to the left. If done carefully you may be able to do this without changing the timing much.  (But if they actually are loose, then who knows how much they have already moved...

 

Do you have a manual for this machine? I'm using this one: 

https://leatherworker.net/forum/applications/core/interface/file/attachment.php?id=139088

but you can probably find one in German too.

Some general videos on timing:

https://www.youtube.com/watch?v=1wNBPX8i524
- video by Uwe of Consew 225

https://www.youtube.com/watch?v=pL9WiZeKZAY
- video by Uwe of Adler 67

 

 

[AlZilla]

Have you considered that the binding may not be in the shuttle area?  I don't know if that machine uses a belt or gears to transmit power to the bottom half, but it might be worth disconnecting it. At least you could isolate it to the top or bottom of the machine.

[friquant]

24 minutes ago, AlZilla said:

Have you considered that the binding may not be in the shuttle area?  I don't know if that machine uses a belt or gears to transmit power to the bottom half, but it might be worth disconnecting it. At least you could isolate it to the top or bottom of the machine

Agreed.

[Yoshi888]

I was a bit to curious to wait so I just went over to the workshop to take a look.
It seems the horizontal shaft has some play.
I screwed in the center screw of the bobbin to pull up the vertical shaft and tested the two cases.
When I pull it outwards (to the left) it does not bind up. 
When I push it in (to the right) it binds up at a fixed position.

So my best thought at the moment is also what @friquant suggested.
Once I collect my nerves this week, I'll try to reset the horizontal shaft and fix it in place again.
Hopefully, if I watch out for the correct position, I can also save my hook/needle timing.

But that already gives me hope I don't have to order spare parts again. That was quite an ordeal last time.

@AlZilla
If the above doesn't fix it that will then be my next task. 
I think the Belt connects only to the top, so I assume it uses gears but I'll double check below the cover next time because that would probably also be a good thing to know about my machine.

Here is also a video again that shows it a bit better than I can explain.

Edited Monday at 08:11 PM by Yoshi888

[friquant]

@Yoshi888 Excellent video!

As you have already concluded, whatever is supposed to hold the (horizontal) hook driving shaft in place left-to-right has come loose, which has allowed the two bevel gears to disengage and therefore lose track of time.

First you need to get the (horizontal) hook driving shaft fixed in place left to right. Then you will need to set the hook-to-needle timing.

I expect you won't need to purchase any parts.

[friquant]

1 hour ago, Yoshi888 said:

Hopefully, if I watch out for the correct position, I can also save my hook/needle timing.

Oh I see...if you can get the correct tooth to match between the gears, you wouldn't have to loosen the bevel gears at all 😃

I want to put a mark next to my gear teeth (and between the shaft and the gear) so I can take apart and put back together the same way, without having to measure timing. But I haven't done it yet..

 

[AlZilla]

@Yoshi888 don't stress about hook timing. In fact, you should learn and practice it.

I remember how intimidating it seemed a few years ago when I had to set it as part of replacing the top gear in an old Singer home sewing machine. Now, it's routine and I don't think about it. If you can set the gap on a spark plug, you can set the hook timing. The biggest thing usually is to take the needle plate and maybe feed dog out so you have a clear line of sight.