Leaky hotend

I’ve been having issues with blobs and strings that don’t seem to have any regularity to them and have tracked it down to something leaking, putting hot plastic inside the insulation on the hotend. When enough builds up it oozes out to form a drip, which then screws up the print. I’ve got my extruder all torn down, except for the insulation itself and the only thing I could ‘find’ was a tight nozzle. I had to heat it to get it off. Any ideas on what I should look for? Maybe a good assembly video for the hotend of an MK8? I’ve ordered a few spare insulation strips and I have a spare nozzle, but I don’t have a spare block, heater or thermistor (yet, I expect I’ll order some this week just to be safe).

The only place a leak can happen is between the nozzle and the throat. This is the only tight connection and should be double checked on the first heat cycle.

Make sure the nozzle is not tightened to the heatsink. It should have a gap as if a washer is missing.

That makes sense. When I swapped nozzles a while ago I bet I tightened enough to back the throat up into the heat block. Is there a spec for appropriate gap between the nozzle base and the heat block? It’d be tough to measure unless the throat stuck out past the insulation…

No, just not touching.

There is a lot of opposing theory’s on that insulation. Mine generally gets thrown away on the first nozzle unclogging, no big deal.

Thomas Sanlader made an excellent video about how to assemble an hotend:

I found a crack in the throat and am now just waiting on a replacement. When I put it back together I’ll make sure to tighten the nozzle against the throat and not the block. That video only left 1/4 turn out from the block, about 0.25mm with the standard 1.0mm pitch used for 6mm threads. I’ll probably double or quadruple that just to be safe.

Well, I only broke two of the throats, my original and the first replacement (dang they have thin walls). I also managed to pull the thermistor out of the block, so I went for the full rebuild and put a new hot end in. Things seem to be printing great, once I figured out that the thermistor on the new hot end reads several degrees lower than the old one. The current print should be done around 1:30 and it’s 11:00 now, so I’ll wait for the morning to see how it came out.