Prusa MK4S and MK4 Deep Cleaning Guide

Disassembly for Deep Cleaning: Step-by-Step Protocol

You can't clean what you can't reach. The MK4S shares 90% of its frame with the MK4, but the Nextruder assembly is different. Here's the sequence I use after every 500 hours or when I swap filaments (whichever comes first).

1. Hotend Removal The Critical Torque Sequence

Remove the silicon sock first. Then loosen the two M3 set screws on the heat sink using a 1.5mm hex driver. Don't use a T-handle you'll strip the heads. I've seen it. Pro-tip: Apply a drop of threadlocker (Loctite 242) to these screws after cleaning they vibrate loose over time.

Once the heat sink is free, pull the hotend assembly downward. The thermal paste between the heat sink and the heatbreak will be dry after 300 hours. Scrape it off with a plastic spudger, never metal. Metal creates micro-grooves that reduce thermal transfer.

2. Heatbreak and Nozzle Carbonized Filament Removal

This is where most field fixes fail. Standard atomic pulls (cold pulls) only remove loose debris. For the MK4S with its hardened steel nozzle and bimetallic heatbreak, carbonized residue adheres to the internal surface. Here's the procedure:

• Step 1: Soak the nozzle in 99% isopropyl alcohol for 30 minutes. Do not use acetone it attacks the nickel coating on MK4S hardened nozzles.
• Step 2: Insert a 0.4mm drill bit (or a nozzle cleaning needle) from the nozzle tip and push upward into the heatbreak. Rotate gently. You'll feel resistance from carbon deposits.
• Step 3: Use a heat gun on low setting (150°C) to soften the residue inside the heatbreak while doing a cold pull with nylon filament. The nylon melts at 240°C, but the heat gun keeps the heatbreak at 150°C to avoid degrading the PTFE lining (if present on older MK4 models).
• Step 4: Repeat until the pull comes out clean. Don't use more than three cycles over-pulling strips the thin PTFE coating inside the heatbreak.

Reality check: If you've printed with glow-in-the-dark or carbon-fiber filaments, forget cleaning. Just replace the nozzle. Those materials grind the throat into a bell shape within 200 hours.

Linear Rod and Bearing Cleaning The Z-Axis Factor

The MK4 and MK4S both use hardened steel linear rods and IGUS drylin bearings on the X-axis, but the Z-axis uses linear ball bearings (LM10UU). These are greased from factory, but the grease picks up dust. Here's what I've found after running six units in a woodshop environment:

• Z-axis wobble: Caused by uneven grease distribution. The ball bearings develop high spots.
• X-axis grinding: The IGUS bearings wear in after 100 hours, but if they're contaminated with filament dust, they squeak and create micro-scratches on the rod.

Rod Cleaning Protocol The 10-Minute Maintenance

Every 100 hours, wipe the linear rods with a lint-free cloth soaked in 70% isopropyl alcohol. Do not use WD-40 it dissolves the factory grease. After cleaning, apply one drop of PTFE oil to each rod, then move the carriage back and forth 10 times. I've found that the MK4S's wider linear rod spacing (20mm vs 18mm on the MK4) makes it more tolerant to slight contamination, but the aluminum rods on the MK4 can develop pits if moisture is trapped.

Fan Shroud and Heatsink Duct The Overlooked Heat Sink

I've watched people swap hotends because of heat creep, only to find dust blocking the fan shroud. The MK4S has two 4010 axial fans on the print head one for part cooling, one for the heatsink. Both are prone to dust accumulation.

• Diagnostic: If you hear a whining sound from the fan, it's running faster than usual because the dust is reducing flow. Measure airflow with a cheap anemometer anything below 1.5 m/s on the heatsink fan is trouble.
• Cleaning: Use compressed air (max 80 psi) with a small nozzle. Hold the fan blades with a toothpick to prevent overspin overspin can generate back EMF and damage the fan controller.
• Preventive: Install a 0.5mm mesh filter over the fan intake. Cut it from a nylon stocking. It cuts airflow by 5% but extends cleaning intervals from 50 hours to 300 hours.

Heated Bed Adhesion Residue and Glass Wear

The MK4 comes with a PEI spring steel sheet. The MK4S optionally offers a textured PEI or powder-coated surface. Both accumulate glue stick residue or microfractures from overly aggressive scraping.

Cleaning routine: Wash with dish soap and water every 50 hours. For stubborn PLA residue, heat the bed to 60°C and wipe with isopropyl. Do not use acetone it degrades the PEI coating. I've seen beds that look like lace after three acetone applications.

If you're getting adhesion failures after cleaning, check for micro-fractures in the PEI layer. Hold the sheet at an angle under a bright light you'll see cracks if it's worn. The MK4S's magnetic bed is thicker (0.5mm) and lasts about 2x longer than the MK4's, but both eventually delaminate at the corners after 2000 hours.

Filament Sensor Assembly The Unseen Debris Trap

The MK4's IR filament sensor uses a transparent plastic window. Over time, filament dust and plastic vapor condense on this window, causing false positives or filament runout errors. I've had four calls about "random pause issues" that were solved by cleaning this window.

• Step 1: Remove the two M2 screws on the sensor housing (beware: they're tiny and love to roll away).
• Step 2: Use a cotton swab dipped in 99% alcohol. Gently wipe the IR window don't scratch it.
• Step 3: Blow out the housing with compressed air before reassembly.

Pro-tip: If you print with PETG, the offgassing leaves a thin film on this window within 20 hours. Set a calendar reminder to clean it every 10 prints.

Maintenance Schedule Real-World Intervals

This is what I use in production. Adjust based on your environment.

• Every 10 prints (or weekly): Wipe rods with alcohol, check fan for dust, clean filament sensor window.
• Every 100 hours: Deep clean hotend (cold pull + nozzle soak), re-grease Z-axis bearings, check belt tension (140Hz on the wrench test for MK4S).
• Every 500 hours: Replace nozzle (if using abrasive filaments), replace heatsink fan if noisy, replace IGUS bearings if X-axis shows backlash.
• Every 2000 hours: Replace X-axis linear rods (they develop a flat spot from constant ball friction). Replace bed sheet if PEI is cracked.

Troubleshooting Matrix Cleaning-Related Print Defects

If you see these issues after cleaning, you've done something wrong.

• Z-band after bearing cleaning: You didn't re-grease properly, or you over-torqued the bearing block screws. Spec: 0.6 Nm (finger-tight plus 1/8 turn).
• Nozzle oozing after hotend cleaning: You didn't seat the nozzle against the heatbreak fully. The gap traps molten plastic. Re-torque to 3 Nm at 250°C.
• Filament sensor false triggers: You used too much alcohol and it seeped into the electronics. Let it dry for 30 minutes before powering on.
• Fan noise after cleanup: You hit the fan blades with compressed air and they're now out of balance. Replace the fan balancing is impossible at this scale.

Final note from the shop: The MK4S is a solid machine, but its cleaning needs are non-negotiable. I've seen printers that look pristine on the outside but have a 70% first-layer failure rate from hidden gunk. Stick to the schedule, use the right solvents, and for God's sake, stop using acetone on the PEI sheet. Your printer will outlast your patience.