My Machine Turns Heavily or Jams

Another in the series of troubleshooting tips.  Tips are not in order of most common to least common and do not need to be performed in sequence.  Pick the easiest ones first and work to the more difficult ones. 

1a. Cause: Sewing thread has wedged itself between the balance wheel and the arm of the machine.
 Solution: Take off the balance wheel and remove the thread.
1b. Cause: Thread has wrapped itself around the hook shaft.
 Solution: remove the thread from the hook.
1c. Cause: Thread has wrapped itself around the pivot point of the take-up lever.
 Solution: Remove the thread from the take-up lever and oil the point because the thread has soaked up all the existing oil.
1d. Cause: Thread has become wedged between the bobbin case and the bobbin case base.
 Solution: If the thread cannot be easily removed, disassemble the hook and remove the thread.
2. Cause: There is too much pressure on the fabric.
 Solution: Reduce the pressure of the presser foot.
3. Cause: The feed dog rubs against the sides of the slots in the throat plate.
 Solution: Loosen somewhat the screws that hold the feed dog to the feed bar, then adjust the feed dog so that it can move freely in the slots of the throat plate.  Tighten the feed dog screws firmly after this adjustment.  If throat plate slots are badly damaged, replace the throat plate.
4. Cause: Due to accumulation of dirt and gummed oil between the throat plate and the feed dog, the feed dog presses against the underside of the throat plate.
 Solution: Remove throat plate and clean it.  Also clean the parts of the machine to which these parts are attached.
5. Cause: The belt running to the balance wheel is too tight.
 Solution: Adjust or replace the belt.  The belt should have just enough tension so as not to slip.
6. Cause: Dirt, thread, and pieces of broken needles have wedged between the bobbin case holder and the hook.
 Solution: Disassemble these parts, clean them thoroughly, and replace them on the machine.
7. Cause: The bearings of the machine are tight due to rust or the use of improper oil.  The oil may be gummed in the bearings; there may also be dirt in the bearings.
 Solution: Squirt the recommended solvent into all bearings and run the machine for a while.  Oil the machine afterwards with good sewing machine oil.  Do not use thick oil or vegetable oils.
8. Cause: One or several parts inside the machine are tight.  This may be due to improper assembly, lack of oil, or bent parts.
 Solution: Disassemble the machine systematically, always trying whether it turns freely or not.  Stop disassembling once you can turn it freely.  Examine all removed parts and repair or replace them as necessary.  Clean all parts thoroughly in a recommended solvent.  Assemble the machine carefully, making sure it turns freely every time a part has been inserted.  Oil the machine properly after it has been reassembled.
9. Cause: The thread take-up lever is bent.
 Solution: Remove the thread take-up lever and straighten it, if possible.  Replace the lever if it is badly defective.
10. Cause: The throat plate is bent downward due to repeated dropping of the presser foot.  As a result, the feed dog rubs against the underside of the throat plate.
 Solution: Place the old throat plate. Top surface down, on a flat surface and straighten it by tapping it carefully with a hammer.  If badly distorted, replace the throat plate with a new one.
11. Cause: The needle bar is bent.
 Solution: Remove the needle bar and turn the balance wheel by hand.  If the machine turns easily now, it indicates that the needle bar is bent.  Straighten the bent needle bar on a flat surface, if possible.  If the old needle bar is defective beyond repair, replace with a new needle bar.
12. Cause: The tail of the main shaft is bent.  This can happen if the machine was dropped or the balance wheel was bumped.
 Solution:  Watch the balance wheel as it rotates.  If it wobbles, that is an indication that the main shaft tail might be bent.  Remove the balance wheel and rotate the main shaft so that the bent tail is pointing up.  Place a block of wood on the shaft tail and hit the wood block with a hammer, just hard enough to bend the shaft back to the proper position. Do not hit the shaft directly with the hammer, that will damage the soft metal of the shaft and prevent the balance wheel from fitting on the shaft.

Ed
Ed's Vintage Sewing Machine Shop