How to fix a "clogged" Makerbot SmartExtruder (5th Gen)

We've had the Makerbot 5th gen in our makerspace for about 6 weeks now, and we are about to receive our third "Smart Extruder" from MBI. After about two weeks it wouldn't take filament and wouldn't print...seemed clogged. Not wanting to void the warranty on our shiney new toy, we played nice and sent the old one in and they sent us a new one. Here we are a few weeks later and it was clogged again.

This time, however, MBI told us to keep the clogged one and they'd send us a new one anyway. I guess they figured the maker community would eventually figure out how to fix them, and then someone would post about it and maybe MBI could leverage that for a more permanent solution. Well, here you go.

Without any further introduction, here it is.

How to fix a "clogged" SmartExtruder on the Makerbot 5th Gen.

1. Heat the extruder using the "Load Filament" command on the MakerBot.
2. Once the stepper starts stepping, take the extruder off of the machine, and while it is still hot, use a 4mm wrench (I used an adjustable) to remove the nozzle from the extruder.
   
3. Make sure your nozzle isn't clogged. If that is the problem, then you can clean it with a small gauge wire and a blowtorch. Ours wasn't really clogged, but I cleaned it up anyway. 
4. Remove the fan shroud from the bottom of the extruder by lifting (gently) the tabs that hold it on. Mine came off pretty easily, You have to loosen all 4 tabs, then get a little space along the seam where the shroud touched the extruder body, then loosen the tabs again, and so on. You'll see what I mean when you get in there.
5. Now, go ahead and use the same "Loosen, spread, loosen" routine on the plastic casing around the main extruder body. The housing should come off after 2-3 rounds of spreading. Be careful not to lose any parts as the lifter mechanism isn't really held in by anything but pressure. When you open it up the bearings and the lifter mechanism may fall out. I like to work on a table that is covered in carpet so if parts fall they don't bounce half-way across the room.
6. Next, unscrew the heater body from the heatsink. To do this, you need to heat the heater-block with a torch for just a few seconds, then use really thin pliers or a narrow crescent wrench to unscrew the heatsink from the heater-block. The hex-head (nut)  is between the fins and the heaterblock. It won't unscrew when its cold.
   
7. After you have off the heatsink, see if it has plastic in it. I used 22gauge wire to push out some hardened (glassified) plastic that was in the way. I had to heat the heatsink before pushing the wire through to soften the plastic. A couple seconds in front of a blow torch was plenty of heat.
8. Once this side is clean, repeat the same process for the heater-block.
   
9. Now that your heater-block and heatsink are clean, heat the heatsink bank up and screw it back into the heater-block.
10. 
    
11. Carefully re-assemble the whole thing. To get everything in line, I put a piece of filament (6" or so) through the  assemble to hold everything straight while I lined up all the pieces and snapped it back together. Pull the filament out when you get it snapped back together.
12. Now put the nozzle back on the heater-block by heating it up. I wouldn't try to screw it in while it was cold, I'm pretty sure it won't go. Just heat the aluminium heater-block, then the brass nozzle will go in very easily. You may have to heat the assembly again to get it all the way in. When it cools the threads become so tight I couldn't turn it with a wrench without thinking I was going to break something.
13. Now, put the extruder back on the MakerBot, load up some filament using the on-screen tools, and you should be good to go.
    

For a detailed teardown of the extruder for curiosity sake, look here. They don't get into taking the nozzle off or taking the heater-block apart.

Hope this helps someone out there.

Happy Printing!