Hi everyone:
Just wanted to share some information on some troubleshooting I did on my late 2013 Printrbot Simple in case it’s useful to someone.
I am printing Kossel parts for a friend. I have my print speed set very low to minimize warping, since I don’t have a heated bed. I was having a lot of trouble with filament jamming in the extruder after 90 minutes or so.
I started with the typical - bed leveling, cleaning, adjusting tension. After a lot of reading, I found that the extruder motor was running hot, causing the filament to visibly melt before it entered the hot end. I dialed back the current until just above where it would stall, and tried again - no luck.
However, I then attached a 40 mm fan to the non-motor side of the extruder, blowing air into the extruder over the hob bolt and the front face of the motor. It then exhausts up through the extruder.
This immediately solved the problem - an 11 hour print went off without a hitch.