If you have used MMU3 unit on your MK4/MK3.9 printer, your extruder is slightly different. In that case, please proceed to the dedicated chapter:
⬢If you have a single-material printer, continue to the next step.
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- Original Prusa MK4/MK3.9 to MK4S/MK3.9S upgrade
- 4. Upgrading the Nextruder
4. Upgrading the Nextruder
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- Original Prusa MK4/MK3.9 to MK4S/MK3.9S upgrade
- 1. Introduction
- 2. Upgrading the Y-axis
- 3. Upgrading the xLCD
- 4. Upgrading the Nextruder
- 1. MK4S MMU3
- 2. Tools necessary for this chapter
- 3. Protecting the heatbed
- 4. Uncovering the Nextruder
- 5. Removing the idler-swivel
- 6. Assembling the Idler-swivel: parts preparation
- 7. Assembling the Idler-swivel
- 8. Assembling the Idler-nut
- 9. Disconnecting the Nextruder cables
- 10. Removing the print fan assembly
- 11. Removing the heatsink fan&hotend
- 12. Removing the Nextruder
- 13. Gearbox versions
- 14. Uncovering the gearbox
- 15. Removing the extruder idler
- 16. Extruder idler assembly: parts preparation
- 17. Upgrading the extruder idler
- 18. PG-cover: parts preparation
- 19. Installing the idler and PG-cover
- 20. Mounting the idler-swivel: parts preparation
- 21. Mounting the Idler-swivel assembly
- 22. Assembling the Nextruder: parts preparation
- 23. Assembling the Nextruder
- 24. Attaching the Nextruder
- 25. Connecting the NTC thermistor
- 26. Assembling the hotend fan: parts preparation
- 27. Assembling the hotend fan
- 28. Print fan blower: parts preparation
- 29. Assembling the print fan case
- 30. Assembling the print fan blower
- 31. Assembling the fan shroud
- 32. Mounting the print fan blower assembly
- 33. Connecting the print fan blower
- 34. Prusa Nozzle CHT: parts preparation
- 35. Removing the Prusa Nozzle
- 36. Installing the Prusa Nozzle CHT
- 37. Inserting the hotend assembly: parts preparation
- 38. Inserting the hotend assembly
- 39. Nozzle insertion check
- 40. Connecting the hotend cables
- 41. Fan door cover: parts preparation
- 42. Attaching the Fan-door-cover
- 43. Connecting the extruder cables
- 44. LoveBoard: Wiring check
- 45. Covering the LoveBoard: parts preparation
- 46. Covering the LoveBoard: side cover
- 47. Covering the LoveBoard: top cover
- 48. What's left (part 1)
- 49. What's left (part 2)
- 50. Haribo time!
- 51. The Nextruder is upgraded!
- 4B. Upgrading the Nextruder (MMU3)
- 5. Upgrading the connectivity
- 6. Preflight check
- Manual changelog
4. Upgrading the Nextruder
⬢For this chapter, please prepare:
⬢2.5mm Allen key
⬢Torx key T6
⬢Torx key T10/8
⬢Wrench 13-16
⬢Universal wrench
It is HIGHLY RECOMMENDED to protect the heatbed.
⬢Use any cloth or piece of fabric, which is thick enough and cover the heatbed. This will ensure you won't damage (scratch) the surface during the disassembly.
⬢Move the Nextruder approximately to the center of the X-axis to gain better access to the entire assembly.
⬢Remove the LoveBoard-cover by sliding it up.
⬢From the right side of the Nextruder, release and remove the M3x10 screw.
⬢Remove the LoveBoard-cover-right from the printer.
⬢Remove two M3x30 screws with the springs from the Nextruder.
Do not discard any of these parts. You will need them again later on.
⬢Remove the idler-swivel assembly from the Nextruder.
⬢Release two M3n nuts and remove two M3x20rT screws from the idler-swivel assembly.
⬢Tear the assembly into its parts.
You will no longer need the plastic parts.
⬢For the following steps, please prepare:
⬢Idler-swivel (2x) new part
⬢Idler-nut (1x) new part
⬢M3x30 screw (2x) you removed earlier
⬢M3x20rT screw (2x) you removed earlier
⬢M3nN nut (2x)
⬢Spring 15x5 (2x) you removed earlier
⬢Spacer 6x3.1x8 (1x) you removed earlier
⬢Push the M3x20rT screw all the way through one of the idler-swivel.
⬢Slide the spacer onto the screw.
⬢Place the second idler-swivel from the opposite side of the screw.
⬢From the other side, attach the M3nN nut to the screw. Hold the nut using the universal wrench and tighten the screw. Tighten just lightly! The spacer must rotate freely.
⬢Insert the Idler-nut into the Idler-swivel assembly. Make sure that both parts are oriented correctly according to the picture.
⬢Secure both parts together by inserting the M3x20rT screw from the same side, like the first screw.
⬢Secure the screw with M3nN nut. Do not overtighten the nut. It must be possible to move with the Idler-swivel on the Idler-nut.
⬢Keep the idler-swivel assembly aside for now.
Note there are safety latches on each of the connectors which must be pushed in, in order to remove the connector.
⬢Disconnect all the small connectors from the left side of the LoveBoard.
⬢Disconnect the Nextruder motor (labeled E).
⬢Disconnect both cables from the right side of the Nextruder.
⬢Remove the M3x30 screw from the fan-door hinge.
⬢Pull the print fan assembly from the Nextruder.
⬢Remove all the disconnected cables from the cable channel.
⬢Release two M3x18 screws securing the heatsink fan and remove the fan from the Nextruder.
⬢Loosen both thumb screws.
⬢Pull out the hotend assembly from the Nextruder.
⬢Loosen all three M3x10 screws mounting the Nextruder assembly.
When loosening the Nextruder, hold it with your hand to prevent it from falling.
⬢Remove the Nextruder assembly from the X-carriage.
⬢Put the printer aside for a moment and let's get on with Nextruder.
⬢Remove both thumb screws from the heatsink.
Do not discard any parts.
There were two types of the gearbox on the MK4 printer.
⬢The older design with four screws.
⬢The newer design with three screws.
The upgrade process is the same for both types of the gearbox.
Another difference is that the older gearbox uses a plastic spacer, while the newer one has a metal washer. Replacing it isn't necessary, as it as it requires a full gearbox teardown and offers no functional advantage.
WARNING: The following procedure must be carried out with extreme care and caution. No part of the gearbox itself should be removed, unless instructed to.
If you lose any part of the assembly, please contact our customer support.
⬢Release and remove the screws securing the PG-case.
⬢When removing the screws, hold the PG-ring (gold-brass part) to prevent it from sliding out.
⬢Extremely carefully and slowly remove the PG-case from the Nextruder.
The gearbox will remain open for some time. Take care to prevent any dirt or debris from entering it.
⬢Insert three M3x25 screws (you removed earlier) into the marked openings on the PG-ring. Do not tighten too much, 2-3 turns are enough. This is just a temporary fix to keep the gearbox assembly in place.
⬢If you have the newer type of the gearbox, using the Torx T6 key, remove the M3x25 socket set screw securing the idler.
⬢Slowly and carefully remove the extruder idler from the Nextruder.
⬢Let's take our hands off the gearbox for a moment and move on to upgrading the extruder idler part.
The gearbox will remain open for some time. Take care to prevent any dirt or debris from entering it.
⬢Release and remove the M3x6 screw from the Idler-lever-b.
⬢Remove the Idler-lever-b (top part) from the idler assembly.
⬢Remove both bearings and pins from the Idler-lever-a (base part).
⬢Pull out the tubular spacer from the Idler-lever-a.
⬢For the following steps, please prepare:
⬢Idler-lever-a (1x) new part
⬢Idler-lever-b (1x) new part
⬢Bearing 693 2RS (2x) you removed earlier
⬢Pin 2.9x8.5 (2x) you removed earlier
⬢M3x6 screw (1x) you removed earlier
⬢Tubular spacer 13.2x3.8x0.35 (1x) you removed earlier
⬢Place both bearings into the Idler-lever-a.
⬢Insert the 2.9x8.5 pins into each bearing 693 2RS, as seen in the picture.
⬢Close up with the Idler-lever-b part and secure it with the M3x6 screw. Do not overtighten the screw. Both bearings must be able to rotate without significant resistance.
⬢From the same side, push the tubular spacer into the assembly. The "bottom" of the tubular spacer must be flush with the bottom part of the Idler assembly.
⬢For the following steps, please prepare:
⬢PG-case (1x) new part
The new cover doesn't require the round plastic washer like the previous version.
⬢M3x25 screw (3x) you removed earlier
The three M3x25 screws are fixing the PG-ring at this moment. Keep them in place for a while.
⬢Socket set screw M3x25 (1x)
Use either the one you removed earlier or the newly supplied one if you have the older type of gearbox.
⬢Back to the Nextruder.
⬢Insert the idler assembly between the PG-ring and the extruder motor. There is a cutout for the spacer in the main-plate. Line up the idler spacer with the hole in the PG-ring.
⬢Secure both parts with the socket set screw M3x25. Do not overtighten the screw! The screw protrudes from the PG-ring after tightening.
⬢Carefully remove all three M3x25 screws.
⬢When removing the screws, hold the PG-ring (gold-brass part) to prevent it from sliding out.
⬢Place the PG-case on the gearbox and secure it with three M3x25 screws. Do not tighten them completely at this moment.
The screws on the PG-case will be completely tightened during the self-test in the final chapter.
⬢For the following steps, please prepare:
⬢Idler-swivel assembly (1x) you assembled earlier
⬢M3x30 screw (2x) you removed earlier
⬢Spring 15x5 (2x) you removed earlier
⬢Attach the spring 15x5 on both M3x30 screws.
⬢Push the two screws with the springs through the holes in the protrusion on the heatsink. There are no threads inside.
⬢Attach the Idler-swivel assembly to the screws. See the correct orientation of the Idler-nut. The side with version marking must be visible. See the picture.
⬢Tighten both screws. Stop tightening as soon as the screw tips reach the front face of the idler nut.
⬢For the following steps, please prepare:
⬢MK4S fan holder (1x)
⬢Heatsink spacer (1x)
⬢M3x12 screw (3x)
Do not reuse the M3x10 screws you removed earlier. Due to the new parts, longer M3x12 screws are now required.
⬢From the front side of the Nextruder (side with the printer logo pg-case), insert three M3x12 screws in the heatsink.
⬢From the opposite side of the Nextruder, fit the heatsink spacer onto the three screws.
⬢Make sure the protrusion protrudes towards you (like the screws).
⬢From the extruder motor side of the heatsink, attach the MK4S fan holder to the heatsink.
Avoid pinching the NTC thermistor cable. Guide it through the cutout as shown in the detail.
⬢Place the Nextruder assembly onto the spacers on the X-carriage. Line up the three screws with the three spacers.
⬢There is a cutout in the plastic part. Guide the thermistor cable through this cutout.
DO NOT PINCH ANY OF THE CABLES!
⬢Align the heatsink screws with the spacers on the X-carriage and join both parts together by tightening them. Start with the middle one.
⬢Locate the cable channel on the left side of the X-carriage. We will guide some of the cables through this channel in the following steps
⬢Guide the NTC thermistor through the cable channel in the X-carriage up to the LoveBoard slot.
⬢For the following steps, please prepare:
⬢Hotend fan (1x) you removed earlier
⬢M3x18 screw (2x) you removed earlier
⬢Attach the hotend fan onto the heatsink with two M3x18 screws on the left side. Tighten the screw gently, but firmly, otherwise the plastic housing may crack. The cable must be pointing towards the lower-left corner.
There is a sticker on the hotend fan, the sticker must be on the rear side of the fan - not visible.
⬢Guide the fan cable through the cutout in the fan holder.
⬢Guide the fan cable between the thumb screws under the cable channel up and connect it to the lower slot on the LoveBoard.
⬢For the following steps, please prepare:
⬢MK4S Print fan blower (1x)
⬢Fan-case (1x)
⬢Fan-case-cover (1x)
⬢Fan-shroud (1x)
⬢3x8sT screw (2x)
⬢M3x5rT screw (5x)
⬢M3nS nut (5x)
⬢From the flat surface of the Fan-case, insert two M3nS nut all the way into the holes.
⬢Double-check from the side that the inserted nut is aligned with the hole in the part.
⬢From the opposite side, insert two M3nS nuts all the way into the holes. Check that nuts are fully inserted.
⬢Insert one M3nS nut into the hole in the Fan-shroud.
⬢Insert the MK4S print fan blower into the print fan blower case.
⬢Guide the print fan blower cable through the cable channel in the Fan-case.
⬢Close the fan with Fan-case-cover.
⬢Secure the cover with two 3x8sT screws.
The screws cut thread directly into the plastic, so there might be some resistance.
Attach the Fan-shroud to the print fan blower assembly. Notice two teeth on the fan shroud and two rectangular holes in the blower assembly.
⬢First, insert those teeth into the rectangular cutouts.
⬢Close the Fan-shroud and secure it with the M3x5rT screw.
Use reasonable force to avoid breaking the parts.
⬢Take the print fan blower assembly and guide the fan cable through the cutout on the left side of the fan holder.
Use the same cutout through which the heatsink fan cable already guides.
⬢Slide the side pockets of the print fan blower assembly onto the two “forks” of the fan holder.
⬢Ensure that the holes of both parts are aligned.
⬢From the left side of the fan holder, secure both parts together using two M3x5rT screws.
⬢From the right side of the fan holder, secure both parts together using two M3x5rT screws.
⬢Guide the print fan blower cable through the cable channel in the X-carriage and plug the connector to the middle slot on the LoveBoard.
⬢For the following steps, please prepare:
⬢MK4 hotend assembly (1x) you removed earlier
⬢New Prusa Nozzle CHT 0.4 (1x)
⬢Nextruder Silicone sock (1x)
The Nextruder Silicone Sock is optional but recommended for stable temperatures, hotend cleanliness, and protection during high-temperature printing.
⬢For more information, read the article Nextruder Silicone Sock.
⬢Using the wrench 13-16 grasp the heaterblock.
⬢Using the 7mm cutout in the universal wrench, grasp the nozzle and loosen it.
⬢Manually release and remove the Prusa nozzle from the hotend assembly.
⬢Screw the new nozzle all the way into the heaterblock until the nozzle touches the heaterblock surface.
⬢Grasp the heaterblock with the wrench 13-16.
⬢Using the 7mm cutout in the universal wrench, tighten the nozzle against the heaterblock. Do not use any extra force!
The specified torque value is 1.5 Nm (13.3 lb-in). The use of a torque wrench is recommended.
⬢Put the silicone sock back on the heaterblock. This is optional.
Keep the removed Prusa Nozzle as a spare part. While it is fully compatible with the MK4S/MK3.9S printer, we recommend using the new Prusa Nozzle CHT, which features improved material flow technology.
⬢For the following steps, please prepare:
⬢Hotend assembly (1x) you assembled earlier
⬢Thumb screw (2x) you removed earlier
⬢Insert two thumb screws into the heatsink. Do not tighten them completely. Two turns are enough for now.
⬢Look closely at the underside of the heatsink and find the hole for the hotend assembly.
⬢Insert the hotend assembly tube in the hole and slide the whole thing into the heatsink.
⬢Push the hotend assembly all the way into the heatsink. There should be approximately a 2 mm gap between the heatsink and the brass part of the nozzle.
⬢While pushing the hotend assembly in, firmly tighten both thumb screws.
Avoid pinching any cable between the screws and the heatsink!
⬢From the underside, check that the hotend is oriented correctly. It must fit between the cutouts in the X-carriage.
⬢Verify that the nozzle is fully inserted. The copper ring on the nozzle should not be visible if it’s properly seated.
If not fully inserted, poor heat transfer may occur, potentially leading to issues like nozzle clogs.
⬢To adjust the nozzle position, loosen the thumbscrews, reposition the nozzle, and then retighten the screws, while pushing the hotend assembly up.
⬢Guide the hotend thermistor through the cable channel in the X-carriage and connect it to the LoveBoard.
⬢Guide the hotend heater through the cable channel in the X-carriage and connect it to the LoveBoard.
⬢For the following steps, please prepare:
⬢Fan-door-cover (1x)
⬢M3x30 screw (1x) you removed earlier
⬢Attach the Fan-door-cover hinge to its counterpart in the X-carriage. Holes in both parts must be aligned.
⬢Insert the M3x30 screw in the hinge on the fan-door. Fully tighten the screw, then loosen it by a quarter turn. The fan-door must move freely!
⬢Connect the Extruder motor cable to the connector on the top side of the LoveBoard.
⬢Connect the Loadcell cable coming from the right of the heatsink to the upper slot on the right side of the LoveBoard.
⬢Connect the filament sensor cable to the lower slot on the right side of the LoveBoard.
Before covering the electronics, check the connection of all cables. Click on high-resolution preview in the top left corner.
⬢Close the idler mechanism before proceeding to the next step if you haven't already done so. Use the following sequence:
⬢Close the extruder idler to the extruder
⬢Close the idler-swivel and lock it over the extruder idler assembly
⬢For the following steps, please prepare:
⬢LoveBoard-cover (1x) new part
⬢LoveBoard-cover-right (1x) new part
⬢M3x10 screw (1x) you removed earlier
⬢Curve and arrange the cables on the right side of the extruder as you can see in the picture.
⬢Cover the cables with the LoveBoard-cover-right.
Do not pinch the cables!
⬢Secure it with the M3x10 screw.
Make sure the LoveBoard-cover-right fits snugly against the right side of the extruder. If not, it may cause the X-axis test to fail during the self-test because it will prevent the X-carriage assembly from moving all the way to the right.
⬢Push all cables to the extruder to make more space around them. See the picture.
⬢Slide the Loveboard-cover on the extruder. And push it all the way down. The cover must go behind the X-carriage-back.
Be careful not to pinch any cables.
⬢Ensure that the two plastic covers fit together perfectly.
⬢You will no longer need these parts:
⬢Print fan assembly (1x)
⬢Old PG-case (1x)
⬢Old LoveBoard-cover (1x)
⬢Old LoveBoard-cover-right (1x)
⬢Old Idler-nut (1x)
⬢Old Idler-swivel (2x)
⬢Old Idler-lever-a (1x) and Idler-lever-b (1x)
The list continues in the next step ...
⬢Main-plate (1x)
Although you didn't remove the Main-plate part from your printer, it was included in your upgrade kit. Over time, the part may experience slight wear, so it's wise to keep it as a spare.
⬢Prusa Nozzle (1x) or your other purchased nozzle
⬢Now you feel like you can fix anything, right? :)
⬢Eat two gummy bears.
⬢That was tough, but you made it!
⬢We're almost there. Let's continue with chapter 5. Upgrading the connectivity.
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