Juki 5550N experiencing problem in the bobbin area

[thobgood]

Hello! I've been a reader here for years and seeing other people's machine problems and the comments from other forum members suggesting fixes has helped me many a time. This week I've experienced a machine problem of my own, and for the first time I can't find anybody who's had the same issue, so I'm posting this with hopes that someone wiser than myself might be able to help me out. I've been sewing for nigh on 45 years now, but I'm still no machinery expert. I can figure out most little things (tension—it's always the tension!) but this one has me stumped.

I've got a nice little Juki 5550N that I bought new (back when I could afford to buy things new!) I've had it about 9 or 10 years now I think, always sewing the same sort of stuff, but recently it's been acting up. I've noticed the occasional skipped stitch, and have noticed the thread momentarily going slack now and then. The past few days I've been tearing my hair out trying to diagnose the problem (and I lost my hair years ago, so that take some effort!) I'll list what I have tried at the end of this post, but right now I'll tell you what I've figured out. I think this issue is in the bobbin area, with possibly the thread catching on something or having trouble making it around the shuttle. It still sews and produces nice stitches most of the time, but there is definitely an issue. When I did a test sew just using the handwheel, I noticed that resistance is felt when the take-up lever is reaching its lowest position and just starting to move back upwards. If I continue to move the handwheel, two little pops are heard, as if the thread is catching somewhere and being released. As I mentioned earlier, when sewing with this issue, I've started to see the occasional skipped stitch, sometimes two in a row, and occasionally the thread will momentarily go slack between the take-up lever and the needle, justjsut for a moment. Then it gets tension again. I've made some videos showing the behaviour while handwheeling. I'll link those at the end of this post.

Here's what I have tried: I've changed the needle for a new one. I've changed the size of the needle (even though I've been sewing with that size and that type of thread for years with no problem.) I've tried different cones of thread. I've changed the bobbin. I've tried a different bobbin case. I made certain the needle was inserted correctly. I've rethreaded the machine. I've disassembled the upper tension assembly to make sure it wasn't clogged with lint, and carefully reassembled it. I've adjusted the tension to make sure it is correct, and it does form nicely balanced stitches. I've taken off the needle plate and feed dogs and cleaned the bobbin area. I've oiled the machine. I've checked to make sure there are no foreign objects clogging the bobbin area (and there are none I can see.) That's about the extent of my machine knowledge, and now I'm stymied and frustrated. 

On to the videos! I tried to shoot from a few different angles to give y'all the best views possible. I'm handwheeling slowly so you can hear the pops hopefully. They're happening just as the take-up lever reaches the bottom and starts back up, and I've tried to show both the bobbin area and the take-up area so you can see how they correspond, and have also done a closeup of the bobbin area.

Test sewing on scrap fabric: https://youtube.com/shorts/CofAeMaxJ8A?feature=share

Needle plate removed, shot from left: https://youtube.com/shorts/794Q-e1iLlw?feature=share

Needle plate removed, shot from right: https://youtube.com/shorts/pplD9J6i8Zo?feature=share

Needle plate removed, closeup from front: https://youtu.be/9bncMsKGbBE

Any suggestions would be SO appreciated. I'm at my wit's end and haven't gotten anything done for a week or more. Between that and the floods, it hasn't been the best of times here in NC! Thanks so much.

[friquant]

Wow it's hard to see down in there. I'm used to having a vertical-shafted hook where you can see the thread take a round trip.

Can you take one more video with the feed dogs removed, as close as you can but still in focus, and move the handwheel very slowly. (About four seconds to do a full turn ought to do it.) Then maybe we can see what's clunking around.

If we can't see it from above, you may be able to get a shot from below the left side. (This may require partially disconnecting the arm that the feed dogs ride on so we can get a better view)

If using an iPhone, Uwe made a demonstration of how to lock the focus on an iPhone for taking close-up videos: 

https://www.youtube.com/watch?v=twl_V_vlq2Q

 

[thobgood]

I shall do this first thing tomorrow! Thank you so much for the suggestion friquant!

[Wizcrafts]

@thobgood

When a machine that normally sews well suddenly starts missing stitches, there are three usual suspects. The first is when the needle and hook are out of time. The second is when the check spring motion is incorrect. The third is when the foot pressure is too light to hold the material flat during the needle take-up cycle.

Since you have removed the cover plate, you can easily see if the hook is intersecting the needle above the eye, but still within the cutout "scarf." Where the point of the hook is can matter a lot, depending on the quality of the loop that's formed by the ascending needle. You could have perfect timing, but a too small thread loop that might not persist when the hook arrives to pick it off. I normally time my machines so that the hook intersects the needle 1/8 inch above the eye after it ascends about 1/8th inch. This isn't set in stone, but is a good starting point. If your timing isn't close to that, either move the needle bar or the hook.

The quality of the loop is determined by two main parts. The first is the motion of the needle. The needle needs to go all the way down with the thread basically taut, then begin to ascend after the thread loosens up. That's where the upward motion comes into play. The hook must wait until the needle comes up as mentioned before. But, if the needle rises as specified and the hook arrives at the designated position and the loop doesn't get picked off reliably, the usual suspect is the check spring assembly!

The check spring assembly usually has these three adjustable components.

1. The stop motion bracket. This is a movable bracket that stops the downward motion of the spring where the thread comes out of it. It must keep tension on the top thread until the needle pierces the top of the material. Then it can stop moving. You might let the spring move down after the needle penetrates the bottom layer if it leads to better results. But, never stop before the needle meets the top or it might separate the thread and shred it!
2. The slack adjustment. This is usually a curved slot with a tiny screw that is set to give a decent amount of slack thread. Normally, setting it to the far left gives the least slack thread and vice-versa. The normal position is dead center in the slot. A tighter setting leads to tighter laying stitches and the opposite direction leads to looser stitches.
3. The spring tension adjustment. The tension is adjusted by finding and loosening a screw that is close to the body. It locks the shaft holding the spring in its position. That shaft is slotted on the outside for a flat blade screwdriver. Loosen it and use a screw driver to rotate it one way or the other until it just has enough pressure to hold the thread taut until it stops moving down. If it is too light, the spring may not move all the way down, which can lead to skipped stitches. However, it is it too tight, it may override the main thread tension disks setting. Balance the overall thread knot position by adjusting the top disks after any adjustments to the check spring assembly, and/or the bobbin spring.

This may be a lot to absorb, but, it's important to understand. By playing with these adjustments you will better understand why your machine sews as it does, or misses stitches.

The last thing I mentioned was the foot pressure. This is actually a two pronged issue. The foot, or feet in a walking foot system, must hold the materiel flat as the needle ascends and the hook arrives at pick-off time. If the material lifts with the needle, you will probably get skipped stitches! So, tighten the foot pressure screw on top of the head! But, what if you have tightened the foot action and the material still lifts between the legs? Yep, skipped stitches! When this happens, buy another foot with less space between the inside of the legs!

Recap. Either confirm or adjust the nook to needle timing. Adjust the quality of the thread loop via the check spring. Make sure your presser foot is able to hold down the material between the legs. Once you fine-tune these settings, your stitches will be more reliable. Afterward, you might want to tweak the hook position for the quietest pick-off. If it is too close to or too far from the needle's eye, the thread will snap as it goes around the hook. It is usually louder if the timing is a little late. Try advancing the hook a little. Just make sure it arrives about 1/8th above the eye after the needle rises about 1/8th inch. Your manual may give the exact factory specification for timing the needle. If so, use them. The check spring slack setting can fine tune the quality of the loop.

I hope this helps!

[thobgood]

A lot to absorb indeed, Wizcrafts, but exactly the sort of information I need! I shall make the video that friquant requested earlier, and then I shall delve into all the information you have provided me. 

I always see you answering people's questions in here over the years, and that's very kind and generous of you. I appreciate your wisdom and your assistance. Crossing my fingers I'll be smart enough to figure out a solution with the information you've given me. Thank you so much!

[AlZilla]

3 hours ago, Wizcrafts said:

When a machine that normally sews well suddenly starts missing stitches, there are three usual suspects. The first is when the needle and hook are out of time. The second is when the check spring motion is incorrect. The third is when the foot pressure is too light to hold the material flat during the needle take-up cycle.

That whole post should be a sticky entitled "When Your Sewing Machine Skips Stitches". I'm going to print it out and go through all my overlooked check springs the next time I have to work on my machines.

Thanks for the time and effort putting that together.

[thobgood]

Okay, I have made some more videos as requested by friquant. (I've actually made a few more videos, some while the machine is threaded, but YouTube says I've reached my daily upload limit. Grr. I'll try to upload them tomorrow.)

Needle plate and feed dogs removed, shot from top left https://youtu.be/gU6iqXo5XkE

Needle plate and feed dogs removed, shot from above https://youtu.be/KzAVHOavvZE

Needle plate and feed dogs removed, shot from above right https://youtu.be/ecs0gZc86z4

Needle plate and feed dogs removed, shot from underneath left https://youtu.be/lTKJZDKKaQY

[AlZilla]

 

Have you looked at everything the thread touches and slides across to be sure there's not a burr somewhere? Come to think of it, have you looked to be sure the thread is feeding smoothly from the spool?

[friquant]

 

4 hours ago, Wizcrafts said:

The check spring assembly usually has these three adjustable components.

1. The stop motion bracket. This is a movable bracket that stops the downward motion of the spring where the thread comes out of it. It must keep tension on the top thread until the needle pierces the top of the material. Then it can stop moving. You might let the spring move down after the needle penetrates the bottom layer if it leads to better results. But, never stop before the needle meets the top or it might separate the thread and shred it!
2. The slack adjustment. This is usually a curved slot with a tiny screw that is set to give a decent amount of slack thread. Normally, setting it to the far left gives the least slack thread and vice-versa. The normal position is dead center in the slot. A tighter setting leads to tighter laying stitches and the opposite direction leads to looser stitches.

 

I'm enjoying learning hidden qualities of the thread check spring. Which of these screws do I loosen on my 341 to effect #1 and #2?

[friquant]

1 hour ago, thobgood said:

Needle plate and feed dogs removed, shot from top left https://youtu.be/gU6iqXo5XkE

What jumps out at me is that the latch opens abruptly. Not sure if that's normal for this machine. I don't see the bobbin case opener..maybe it's internal? 

[Wizcrafts]

1 hour ago, friquant said:

I'm enjoying learning hidden qualities of the thread check spring. Which of these screws do I loosen on my 341 to effect #1 and #2?

The bottom travel stopper is set by the bottom screw inside the open channel in the bracket. The slack adjustment is the little screw in the curved slot that's above the main shaft and nut.

[thobgood]

1 hour ago, AlZilla said:

Have you looked at everything the thread touches and slides across to be sure there's not a burr somewhere? Come to think of it, have you looked to be sure the thread is feeding smoothly from the spool?

Thread is coming off the cone smoothly, that was my first thought too! Someone suggested rubbing a cotton ball over the bobbin area where the thread passes to check for burrs. I'm going to try that next. Thanks!

1 hour ago, friquant said:

I'm enjoying learning hidden qualities of the thread check spring. Which of these screws do I loosen on my 341 to effect #1 and #2?

After reading Wizcrafts' note about the thread check spring, I found this video that helped me understand it more. You might enjoy it as well.

https://www.youtube.com/watch?v=4758pErWmY8

 

[thobgood]

38 minutes ago, friquant said:

What jumps out at me is that the latch opens abruptly.

Which part is the latch? Apologies for my ignorance.

38 minutes ago, friquant said:

I don't see the bobbin case opener..maybe it's internal? 

Is the opener the part that releases the bobbin case so you can remove it? There's a little hinged latch on the bobbin case that lets you remove it.

[Wizcrafts]

19 minutes ago, thobgood said:

Is the opener the part that releases the bobbin case so you can remove it? There's a little hinged latch on the bobbin case that lets you remove it.

No, that isn't the opener. On some machines there is a lever with a bent arm that pulls back on the bobbin case to let the thread slip through without getting hung up. If your machine has a latch opener, it is quite abrupt in comparison to those found on our typical walking foot machines. Without the opener lever, the only thing making room for the thread to the hook is the thread itself. That works if the top thread is taut, but can fail if it has too much slack.

[friquant]

27 minutes ago, thobgood said:

Which part is the latch?

The latch is the area between these two red arrows. It's also what keeps the bobbin case from spinning as the hook spins. The latch has to open at least once during the stitch cycle to let the thread pass. 

[thobgood]

14 minutes ago, friquant said:

The latch is the area between these two red arrows. It's also what keeps the bobbin case from spinning as the hook spins. The latch has to open at least once during the stitch cycle to let the thread pass. 

Aha! Thank you. I've learned something!

[thobgood]

Update: I checked my hook timing and the hook was touching the needle and moving it slightly instead of passing close to the needle like it should've been. I found a video that helped me adjust the hook timing to be correct. That felt good! I'm still having the issue I described initially, feeling resistance when handwheeling as the takeup lever reaches its lowest position and then feeling two pops in the bobbin area as I add a slight bit more force. I'll do a thorough check for burrs tomorrow. I'm happy I fixed the timing issue though! 😃

[thobgood]

I forgot to say, if anybody else finds this thread in the future and wonders about hook timing, I found this video quite helpful: https://www.youtube.com/watch?v=GxMT3UfE_tk&t=6s

 

[Wizcrafts]

43 minutes ago, thobgood said:

Update: I checked my hook timing and the hook was touching the needle and moving it slightly instead of passing close to the needle like it should've been.

Some hooks have a deflector shield that will prevent the needle from touching the needle. They are thin steel and bendable. Yours may or may not have one. If not, just move the hook away from the needle slightly. This may alter the timing, so recheck it afterward and advance or retard the hook as necessary.

[friquant]

 

1 hour ago, thobgood said:

feeling two pops in the bobbin area as I add a slight bit more force

When I feel two pops it's when the thread has not cleared the latch by virtue of the latch opening but rather by the thread being yanked past it. Maybe you can find out what opens the latch. Removing the bobbin case may help you see additional mechanisms at work.

[Wizcrafts]

@thobgood

In case you didn't know, Juki machines are top shelf for many applications. Yours is a top notch garment material sewing machine with a fixed foot and bottom/drop feed. Once you get the timing right, it will be a money maker.

Many leather crafters on this forum sew heavy and thick leather projects on specialized machines we often refer to as harness or holster stitchers. Way back around 1986, or so, Juki came out with a heavy duty harness stitcher that they assigned the model name/number: TSC-441. I saw one that was still in a wooden carton in a sewing machine warehouse. At that time, the dealer told me that I could take it home form only just under $6.000. I didn't have that kind of money and they didn't do financing to individual buyers.

Fast forward to around 2011 and a Chinese sewing machine company obtained a Juki 441 and disassembled it. Then they made molds and began casing new versions of that Juki. They gave them new model names and sold them to dealers who assigned their own brand names. I bought one in 2012 that I still use every time I need to sew a thick project. It is a Cowboy cb4500. My best friend has an equivalent brand, called a Cobra Class 4. Both have the same capabilities. Techsew offers their own model as a Techsew 5100. You can now buy one of these machines for between $3500 and $4400, with all manner of accessories! In contrast, I just found a new Juki TSC-441 for sale from a dealer for $9400 plus shipping.

Enjoy your Juki!

[thobgood]

10 hours ago, friquant said:

When I feel two pops it's when the thread has not cleared the latch by virtue of the latch opening but rather by the thread being yanked past it. Maybe you can find out what opens the latch. Removing the bobbin case may help you see additional mechanisms at work.

I had no idea there was such a latch mechanism. I'll definitely investigate it. It definitely feels like the thread is being yanked past SOMETHING! Thanks for the suggestion.

[thobgood]

11 hours ago, Wizcrafts said:

In case you didn't know, Juki machines are top shelf for many applications. Yours is a top notch garment material sewing machine with a fixed foot and bottom/drop feed.

Yes! I got the Juki about…8 or 9 years ago? Something like that. (The brain is rapidly disappearing with age.) I primarily make masks for professional wrestlers, and the Juki has really improved my ability to make masks! The knee lift and the large amount of presser foot raise have really been a boon. It's worked flawlessly all this time, so now that it's acting up it's really thrown me for a loop.

I do a little leatherwork, but I'm not very good at it. I just do it for friends and whatnot. I do have a Consew 206RB walking foot machine that I use with leather. I find it amazing that it can seemingly sew through anything and take needles that look like decking nails! It's nothing like y'all's Cowboys I'm sure. I'd love one of those, but I can't really justify it with the small amount of heavy duty work I do. They look like wonderful machines though!