Hi Ola, Unfortunately I haven’t worked with Montgomery  machines before, but guess you could try this first: First of all, under any circumstances - don't pull fabric through your machine. Stop and take the needle plate (throat plate) off the machine and the bobbin and bobbin case out. Clean thoroughly. Make sure the drop feed lever is all the way to the right. If you're not sure, slide it all the way to the left, then completely back to the right. Also check that your feed dog gear isn't cracked. Reassemble, making sure the throat plate is attached and screws are tightened firmly -- but don't put thread on top of the machine or a needle in the bobbin case. Set the stitch length as long as it will go. When you turn the handwheel, you should see the feed dogs rising slightly above the level of the throat plate. Here’s a nice guide on re-threading, just in case: https://www.youtube.com/watch?v=olXhSmoW... Then place a single sheet of paper under the presser foot and "sew". Is it moving? Are the perforations...

I'm just wondering if it's a thread size issue. Maybe thread and needle size aren't matched up? Which thread do you use? As Phillip suggested, make sure (here’s a nice tutorial) that you have threaded the spool correctly. I would clean everything including the bobbin tension plate on the bobbin case. I would oil the machine especially at the shuttle race. I would take a fresh needle. I would take the presser foot lever up and carefully thread the machine completely new and look how the take up lever handles the thread. I would fasten the two thread ends when I start to sew. I would watch the spool. I would use a cone stand if the spools are to big and I would with certainty also check the bobbin tension. If the bobbin tension is too strong for your new thread than the top tension can be much too weak. (A small test - try to put the cotton thread in your bobbin, take the polyester thread as top thread and watch what happens). If I would get then a good result I would use a different bobbin thread color, sew...

If you see the error"Sewing motor lock", it is likely that your power supply has failed. When you see the error message "Sewing motor lock" this DOES NOT mean your sewing motor is frozen. It means the motor is not getting the correct voltage from the power supply in almost every case. So I guess you should replace your power unit.

Hi! Guess, that’s an old one, yet I found this topic when I was looking for a fix for my Brother CS6000i (computerized one, specs are here) and decided to share some tips. Try a new bobbin case, make sure shaft of needle is towards the back, use air to blow out where needle is placed, your needle may not be all the way up, make sure the little screw is actually holding the needle in place, make sure your bobbin turns clockwise when you pull the thread, make sure your top tension isn't so tight it bends the needle. Make sure the little finger bar that holds the bobbin assembly in place is holding it in place. Also, make sure you’re using right needles for machine.