Cleaning Piaf 1550 bobbin assembly - PfaFF Sewing Machines

Not sure if this works on all machines, but I have used this method on many different models. You should not have to adjust the tension on the bobbin or the top thread. Wind the elastic on the bobbin by hand, not stretched as you wind it. Just normal, then try a test piece. The only thing that you should adjust is the stitch length if needed. The bobbin tension is a very tricky thing to meddle with. Hope this helps.

Those parts are meant to be removable for cleaning and oiling.

How to pull apart and reassemble the bobbin case area on front loading...

How to Clean and Maintain your Sewing Machine at Home Front Loading Bobbin

It may be worthwhile to purchase a new bobbin case for your machine. Trying to re-attach the spring will most likely cause the spring tension to change making it difficult to get the tension correct. Bobbin cases do wear out and really are not all that expensive to purchase. A lot of sewists keep more than one bobbin case on hand so they can adjust a specific case to accommodate the tension for specific thread weights.

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after removing the needleplate and gray bobbincase retainer, manually rotate the handlwheel so that the tip of the hook is between 11oclock and 10oclock. carefully insert the bobbincase into the hook assembly so that the gap in the bobbincase is centered below the feeddogs. manually rotate the handwheel slowly to confirm that the bobbincase is fully seated into the hook assembly. reinstall the gray retainer and then the needleplate. again manually rotate the handwheel to confirm that everything is seated correctly.

It probably goes together much like this: http://www.manualslib.com/manual/85659/Kenmore-385-15208.html?page=68

Try using a can of compressed air in the hole where the bobbin winder pin sets and then push back in operating position. Also, take out bobbin holder under the metal plate below the needle. That entire assembly should come out and go back in easily. Again use the compressed air to get any fabric fuzz away from moving parts. Check your manual or online for oiling instructions. Hope this helps.

I suggest to change the needle

try taking the whole bobbin assembly and the throat plate off and cleaning, that should work

Yes, it does. There are a couple of reasons the bobbin thread could be bunching up on the underside of the fabric. It could simply be that the machine needs cleaning. Take the bobbin assembly out, brush all the old lint out as best you can, reoil the machine once it's all clean, and make sure there aren't any little bits of thread caught in the bobbin assembly. Rethread the machine (carefully) and change the needle. This solves the problem usually--especially if the machine was sewing along fine and the problem develops suddenly. '
The other thing to check is your tension. It could be that the top tension is too loose. But different color thread in the top and in the bobbin, stitch a few inches (be sure to held the top and bobbin thread ends behind your needle as you start to stitch) and check. WIth the pressure foot down, adjust the tension, and stitch again. Keep stitching, checking, and adjusting until you see little if any bobbin thread on the top or top thread on the bobbin.
Another thing to reminder: use the appropriate thread and needle for the fabric you're sewing.
Let me know if this works, ok?

Robbie