After sewing a few stitches, the machine gets jammed. the top stitch looks fine, but underneath there's a ton of thread all bunched up (top spool thread)

I had a problem similar to this-- when sewing, tons of thread was bunching and looping out of the stitches instead of a nice neat stitch. I finally figured out that this old metal bobbin I put in was incompatible. I switched to a plastic bobbin (the kind like that which came with the sewing machine) and the stitches looked fine.

happy sewing

It very well could have a burr in on your bobbin case, If, it was me, I would take it to Sears sewing machine department and ask them what they think it could be. They sometimes have new bobbin cases right there for you to buy, depending how big your Sears is. It won't cost you anything, at least to find out from the saleman.

you might try changing the needle
check to see if the thread is hanging or caught on anything like the spool pin, the notch on the thread spool
sometimes the thread can come off the thread take up lever, I have that problem alot on my machanical sewing machine
happy sewing

Clean any tangles from the bobbin area.

Always thread a sewing machine with the presser foot up so the thread can properly seat into the tension control.

Hand walk a few stitches to see if the thread still feeds too fast from the spool.

When thread pools (falls off the spool) a thread net will help - you can get these at a sewing machine dealer. I use to find them at fabric stores, but have not seen any lately with sewing/serging notions.

re thread the top and bobbin threads

after pulling up the bobbin thread pull both threads to the back and hol them when stitching the first few stitches

with out holing the threads the machine will pull the thread into the machine and bunch the thread

the problem is always on the other side of the fabric - if thread bunches up underneath, the top tension or threading is wrong

Try these time savers:
Test your thread quality to start, thread your machine and LIFT the presser foot (this opens the tension disks). Pull your top thread straight back. If you feel no tension no mater how much thread you pull, your thread is good. If that your machine passes that test, then let me know, we can go to step 2. If not, try different spool of thread, same test until you get a smooth pull (tip: always check your thread this way when you thread your machine)
Step 2:
Pull on your threaded bobbin thread while it’s in the machine. Does it pull smooth and even? If so, go to step 3. If not, try a new bobbin (bobbins get bent or distorted if wound too tight).
Clean thoroughly in the hook and bobbin case area and oil 1-2 drop is all.

Could be a tension issue.

Try this to see if it helps:
Remove top thread.
ALWAYS RAISE the presser foot and rethread from the beginning.
Start the top tension set at the midway point and then adjust.
Check that the bobbin is threaded and installed correctly.

Understanding Thread Tension Threads

Sewing Lesson 10 How to Fix Tension on Your Sewing Machine

What size needle are you using?