|Small immature green plastic stalactite visible on the right nozzle, on its upper left side.|
Makerbot doesn't really intended for end users to change / remove the nozzles, so it takes a fair amount of careful disassembly to do this. It's also easy to break the ceramic insulators around the hot end heaters, thermocouple wires, etc, so do this at your own financial risk!
First, remove both extruder stepper motors, drive systems, and fans until you have the bare X axis platform and hot ends as shown below. This is a good time to loosen the set screws holding the hot ends in place. These are on the back side of the aluminum block, not quite visible on the "top" side of the photo below. Once these set screws are loose enough the hot ends will drop free- so be careful, the thermocouple / thermistor wires are very fine and easily broken. These set screws are also how you adjust the nozzle height to level the two nozzles.
|Steppers, fans, and drive blocks removed|
Next, remove the hot end block from the X-axis platform. There are two hex head screws to remove, one on each side of the X-axis platform.
|Bottom of X-axis platform, one screw visible|
|Hot end block lifted free|
|Setscrew for right hot end fully loosened, starting to pull hot end out (carefully)|
|Hot End is free. Thermocouple / Thermistor lead visible on the right|
I first attempted to remove the nozzle and steel barrel from the hot end block by using a small wrench and a socket, but no luck. They were solid, plus I had trouble putting enough force into the wrenches while trying not a break anything.
|Trying a 3/16" wrench|
|Heater element removed|
|Thermocouple / thermistor & insulation removed|
|Hot End is free! the set screw on the left holds the cartridge heater in place|
|Heating assembly (heat gun barely visible on the top of photo)|
|Carefully unscrewing parts after heating|
|Cleaning off the nozzle|
|White PTFE tape visible on the bottom side of the steel barrel|
|Nozzle back in place. Note the extra kaptontape I used to patch together the cracked ceramic.|
|Fiberglass insulation re-applied|
|Ready for re-assembly|
The repair worked- after putting everything back together and re-leveling the build platform, all new prints were completed without the annoying plastic stalactites forming.