Replacing the Plunger

    If you’re still having extruder issues with your MakerBot Replicator after cleaning the drive gear, another thing that can cause extrusion trouble is the deterioration of the Delrin plunger inside the MK8 Stepstruder.

    As you did when cleaning the drive gear, unload the filament from the extruder that's giving you trouble and move it out of the way. Unscrew the two bolts at the lower corners of the fan. Remove the fan and set it aside, along with the heatsink and spacers. Unscrew the two bolts in front of the black extruder cable and disconnect the motor cable. See cleaning the drive gear for more detailed explanations of these steps.

    Now unscrew the drive block front, the black plastic plate at the front of the motor. Underneath it, you'll see the Delrin plunger assembly to one side of the drive gear. Make sure you remember which side the plunger is on; it should always be at the inside -- the side facing the central cable. Now remove it, being careful not to let the plastic and metal washers fall off.

    The Delrin plunger is a plastic part that's meant to wear away over time. If your Replicator has seen a fair amount of use, you'll notice a divot being worn into the side of the plunger. If the divot is worn too deep, that's probably the cause of your extrusion problems, and you'll want to turn the plunger so that a different side is facing up to be worn down by the filament. 

    You can also search MakerBot Thingiverse for spring-loaded drive block models, which you can print and use as an alternative to your original drive block.

    There's one last thing you should check before you finish: your nozzle heights. Bring the platform as far up as it will go and check that the nozzles are at the same height relative to the platform. If they're not, you may have to correct them with a shim.

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