Can I fix this Juki F400 myself?
 

Machine noise from bobbin area making me crazy. Here are the facts:

Juki F400 domestic sit down

1- machine sews fine. Noise doesn’t affect quality of stitches but it is a rubbing/scraping noise that is worrisome
2- when all thread is out of machine it purrs beautifully
3- loaded with thread and fabric, makes pretty loud noise after about a minute of warmup
4- remove bobbin thread and fabric and just run it with top thread inserted, it will make the noise.
5- this is drop-in bobbin case and I suspect, but don’t know for sure, that thread is rubbing over bobbin case as it revolves around hook. Is this making the noise ? Really hard to tell,

Does anyone one have any inkling of what this could be? I am afraid that I have to wait until this pandemic is over to bring it for repair, thank you so much for any ideas!

Have you oiled it recently? Does it need greasing? Some machine need both.
Also, have you cleaned out in/around the bobbin case?
Have you run dental floss through the tension disks to see if there is anything caught up in there?
I'm not very experienced with all this, but it sounds like something to do with the top thread - follow the thread path slowly and thoroughly, and if possible, thread only partly, run machine and see if you can tell where the noise starts up or originates from?

I have a Juki DX-7, which is in many ways similar to the F series Jukis. My machine made this same rubbing/scraping noise after only a few months' use. Even though the operating manual has no instructions regarding oiling, I was advised by a member here on QB to remove bobbin and bobbin case, and apply oil around the small metal circle under the bobbin case. It did the trick, and I now oil that area regularly. It's very unfortunate that Juki has not included that information in the manual.

Metal circle under the bobbin case!! I know just what you are talking about and I have never oiled that! I bet there’s a ton of friction there when it gets hot. Ok that’s going to be my first step. Thank you 🙏!!!! You are right that the manual doesn’t mention it. I even downloaded the maintenance manual for that model, which has a lot of adjustment measurements and guidelines but nothing about basic oiling! Thank you again -and even if it doesn’t fix it- thank you so much for your suggestion. 😊

Thank you so much for replying! I agree about the top thread having to be engaged in order to make the noise happen. It has to be inserted in the needle, which gets scooped up by the hook underneath, and that’s where I hear the noise . But your idea about following the top thread path makes sense because it’s possible that additional tension there may be causing rubbing and friction down the line. Thank you !! I have a lot more looking to do. Really appreciate your help!! 😊

If you watch what's happening when the noise happens, you'll see that it's when the thread pulls between the bump on the bobbin basket, and the spring. It's right in the front, right side of the bobbin area. Usually, you can fix it by sanding off any rough spots on the bobbin basket. I use a very fine sandpaper - about 400 to 600 grit. It only takes a few gentle strokes. However, if the bobbin basket is too damaged it will need to be replaced.

Thank you for that info! I’ll have to focus on that area. I suspect that the noise is from the thread rubbing on something around the bobbin case. By the way, the case is new, Meaning only about two months old. Interestingly I replaced the bobbin case thinking that it would address the noise issue. And it did! Was great. But another several weeks of heavy use and I’m back to the same problem. So I will take your advice and check it out, 😊 thank you so much!!!

I don’t want to be premature, but I oiled that circle that sits below the bobbin case, and I oiled underneath the bobbin case itself, and I put the machine through some rigorous straight stitching. No noise. I am crossing my fingers, but it makes sense that this might have helped a whole lot! I’ll let you know after a few days of sewing but I am thinking very optimistically. Even if it proves not to be the answer, thank you so much for taking the time to help. ❤️

This sounds like good news! I don't have the same brand of machine but I'm going to look at that area on mine - it's not making a noise, but may need checking out anyway!