This was posted in 2010 and I bought my machine a year ago but have this problem!!! I hope this will solve my problem, and maybe any of you that have this machine and this problem

Bobbin Case Supporter Issue with Some Janome 3160QDC Sewing Machines
Posted on December 8, 2010 by b.gottier
Janome sent dealers a technical bulletin today, letting us know that their were a few rare cases where some of their 3160QDC sewing machines would experience bobbin case jams or thread tangles.

Janome Tokyo looked into the issue, and found that in rare instances, the bobbin case was not being held securely in place. There is a small supporter on the underside of the needle plate, and during the process of manufacturing the sewing machines, different thicknesses of this supporter were installed. On many 3160QDC machines, the thickness of the supporter may not have been enough to sufficiently hold the bobbin case in place, with a gap of 0.4 to 0.6 millimeters. If the gap is too large, and the sewing machine has problems with bobbin case jams or thread tangles, and if the rest of the 3160QDC is adjusted correctly, then a 2.0 mm supporter (part number 846222202) can be installed, and should take care of the problem(s).

Please note: The need to replace the bobbin case supporter with a new 2.0 mm thick supporter is only necessary on 3160QDC sewing machines that have a problem with thread tangles of bobbin case jams. Temecula Valley Sewing Center has not had an instance of this problem in any of the 3160QDC sewing machines that we have sold. New 3160QDC machines already have the 2.0 mm thickness supporter, so this is not an issue with new 3160QDC machines.