Replacing the Hook (and Bobbin Shuttle) on a Juki LS-341N

[Yoshi888]

Hello everyone,

I bought a used Juki LS-341N for my Leather working Business 1-2 years ago, and it has been a great machine so far. 
Recently, I made a mistake when sewing thicker material, and it seems I have broken the tip of the Hook next to the Bobbin, so the hook does not properly catch the upper thread anymore.
I have tried to resharpen and reposition it so it can catch the thread again, but to no avail. When I position the hole sled with the bobbin closer to the needle, the needle hits the side of the bobbin and is bent away from the hook. So it seems the Hook is too damaged that it could be fixed with sanding and readjusting. 

Luckily, the original seller sold me a new sled (the hole bobbin shuttle with the Hook).
Now I have contacted a mechanic who would be able to do the replacement and service, but they have not been very responsive. (I am located in the Southwest of Germany and have not found other options except this person)
So I am trying to evaluate how hard it would be to do this myself. Changing the part does not seem too difficult, but adjusting the needle hook timing and the exact hook position has very small tolerances, and I am not sure how well this can be done by an "amateur".

Do you guys have experience with this, or could you give me an estimation of the difficulties and pitfalls of such a task?

Any help and input would be greatly appreciated!

Cheers 
Josh
 

[friquant]

You can do this! Setting the timing is no harder than removing/installing the hook.

You'll want to remove the feed dog so you can see the needle-to-hook relationship better.

Do you have already the service manual? Here is a link: 

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

The service manual explains what the adjustment dimensions are, but does not actually go into the details of how to remove the hook. This video by Uwe will show you how to remove. (Different machine, but the removal of hook is similar.)

https://www.youtube.com/watch?v=CfkGrz3OugA

 

Edited yesterday at 08:15 PM by friquant

[friquant]

Found two more videos relevant to this project:

Uwe's Consew 225 hook timing video. (Different machine but useful for timing basics. Especially useful are putting black marker at the middle of the needle scarf (easier than measuring your needle bar height). And using a clamp on the needle bar to set your reference position. )

https://www.youtube.com/watch?v=1wNBPX8i524

 

Uwe's Needle Guard Adjustment video. (Different machine, but same concept applies)

https://www.youtube.com/watch?v=9EWODLVlOxo
 

 

 

Edited yesterday at 08:17 PM by friquant

[friquant]

Rereading, you asked for a list of potential pitfalls:

1. Unplug the machine before you begin
2. When you pull the hook out, make sure the pin for the bobbin case opener (under the hook) stays more or less in place. (you don't want to lose it)
3. If the hook is stuck, reach for penetrating oil and a hot air gun. (I broke a hook once prying it out)
4. Make sure the hook is properly settled into place before you screw it down. On my 341 clone it's fiddly to get the hook to drop into the hole because the bobbin case opener has to also align.
5. When you insert the hook, it can go in two different ways 180 degrees apart. One works and the other will not pick up the thread
6. Make sure the tang on the bobbin goes into the slot on the needle plate. Be very careful turning the handwheel if the bobbin is installed but the needle plate is not
7. Magnetize your screwdriver for getting the hook gib screws out. These screws are tiny and easy to drop
8. Use a new needle for timing and clearance adjustments (to make sure it is not bent)
9. Set hook-to-needle distance before setting timing.
10. When setting the timing, note the manual specifies the stitch length you should be set to. (Easy to miss)
11. When setting the timing, make sure the timing gear is gently pressed against the other gear.
12. When setting the timing, note there is a little play in the hook, so make sure the timing is checked during forward rotation of handwheel. Sometimes I use one finger on the hook to apply some reverse pressure to it.
13. Make sure you readjust the bobbin case opener so the thread can jump through the latch, and so the bobbin case opener does not bind.
14. Set timing according to the book. After you set it, verify that it catches the thread with forward and reverse feed, with both short and long stitches.
15. Make sure everything moves smoothly and does what you expect before you run under power afterwards.
16. Find out how your hook broke. Did it collide with the side of the feed dog support? (You can file some material off to give more clearance where it is likely to hit) Did it collide with the needle? (You can/should adjust the needle guard to prevent this)

Edited yesterday at 08:21 PM by friquant

[AlZilla]

You'll be glad you did this repair. It's not nearly as difficult as it seems.

I think your machine uses Allen screws, if I remember right. If it's slotted screws, you'll want good, hollow ground screw drivers in the right size. 

Let us know your it goes. Maybe you'll inspire the next person.