My Robot Doc

Guide

LUBA 2/2X cutting deck making a loud, diesel-engine-like or grinding noise

An authorized Mammotion dealer's walkthrough of what actually causes a loud or unusual cutting-system noise: worn blade screws, a loose disc nut, trapped debris, or a bearing, in that order of likelihood.

From owners' reports, not from Mammotion's own pages.

Models
LUBA 2, LUBA 2X
Last updated
08 Sep 2026
Affects
Robot body — not the app
LUBA 2, LUBA 2XDetails
Models
LUBA 2, LUBA 2X
Last updated
08 Sep 2026
Affects
Robot body — not the app

What to do next

  1. Pull the discs and the blade guard and clear the compacted grass off the top of the discs. It is the same buildup that causes the cutting-height failure, here thick enough that the blades flex into each other.

    Stop and get help if

    you are hearing the discs rattle loosely by hand like a tambourine: that looseness is by design, not a fault.

    More about this step

    Applies when: the deck sounds like a diesel engine, especially in wet or heavy grass.

    Worked if: the chatter stops and the deck sounds like it did before.

    Didn't work? Next: step 2 — Fit new blade screws rather than reusing them. Worn screws let...

    Method: dealer walkthrough, cause 1 (share this mechanism with the cutting-height guide)

  2. Fit new blade screws rather than reusing them. Worn screws let each blade shift outward a millimetre or two, which is enough for adjacent blades to touch.

    More about this step

    Applies when: the noise came back after the deck was cleaned.

    Worked if: no blade can shift outward, with or without buildup pushing the discs up.

    Didn't work? Next: step 3 — Check the 10mm nut at the centre of each blade disc for...

    Method: the dealer's standing rule: never reuse blade screws

  3. Check the 10mm nut at the centre of each blade disc for tightness, and look for a groove worn into its collar.

    More about this step

    Applies when: the noise is a squeal at start-up and shut-down and quiet in between.

    Worked if: the squeal is gone at both start-up and shut-down.

    Didn't work? Next: step 4 — Remove the discs, blade guards and the collar itself. Check...

    Method: dealer walkthrough, cause 3 (a reported case)

  4. Remove the discs, blade guards and the collar itself. Check underneath for small sticks and fibrous grass or seed that cannot be seen with the deck assembled.

    More about this step

    Applies when: you are certain there is nothing under there. The dealer reports that certainty usually ends when the deck comes apart.

    Worked if: nothing is lodged under the collar or the discs.

    Didn't work? Next: step 5 — Remove the blade discs entirely and run the mower in manual...

    Method: dealer walkthrough, cause 4

  5. Remove the blade discs entirely and run the mower in manual mode.

    Stop and get help if

    the noise is still there with no discs fitted: that is the drive-motor bearing, and prolonged wet grass or standing water is what the dealer links it to.

    More about this step

    Applies when: nothing above explained it, especially a distinct grinding or squeaking sound.

    Worked if: the noise is gone with the discs off, which places it in the deck rather than the motor.

    Didn't work? Next: step 6 — Contact Mammotion support with your model and firmware version....

    Method: dealer walkthrough, cause 5 (common on LUBA 1, rare on LUBA 2)

  6. Contact Mammotion support with your model and firmware version. Give the self-test result: that the noise is present with the discs removed.

    More about this step

    Applies when: the self-test confirmed the noise is not the blades.

    Worked if: the case is with support holding the evidence they need.

    Method: this page's own callout

On this page
  1. What to do next
  2. The symptom
  3. Cause 1: grass buildup flexing the blades into each other (most common)
  4. Cause 2: worn blade screws letting a disc shift
  5. Cause 3: a loose disc-retaining nut
  6. Cause 4: sticks or debris trapped where you can't see them
  7. Cause 5: a worn bearing (uncommon on LUBA 2/2X)
  8. Sources
Before you start: a loud or "diesel engine"-sounding cutting deck is almost always mechanical, not a firmware fault. This dealer's repair-shop experience covers the actual causes in order of likelihood.

The symptom

Owners describe it as sounding like a diesel engine, sometimes extremely loud. It comes from the cutting deck itself, and the dealer's diagnosis: most cases trace back to grass compacting on top of the blade discs until it's thick enough that the blades physically flex under the pressure and strike each other1.

Cause 1: grass buildup flexing the blades into each other (most common)

The same underlying mechanism as the cutting-height failure covered elsewhere on this site (grass compacts on top of the blade discs), but here it causes the blade discs to flex enough that blades on adjacent discs physically touch and chatter against each other1. See our cutting-height system failure guide for the full mechanism and prevention tips (mow more often at lower height, expect a "fighting the lawn" period on new installs).

Cause 2: worn blade screws letting a disc shift

A more specific, compounding cause: the screws holding each blade to its disc wear down at the back over repeated rotation, letting the blade shift outward by a millimeter or two. Combined with grass buildup pushing discs up slightly, this is enough for blades to start touching that otherwise wouldn't1.

The dealer's standing rule: never reuse blade screws. Replace them every time you replace blades, even if a screw looks undamaged. This is stated as the single most important habit for preventing this specific noise1.

Cause 3: a loose disc-retaining nut

A reported case: a horrible squealing noise, present specifically at startup and shutdown but not during normal running, turned out to be a loose 10mm nut in the center of a blade disc. The loose disc had worn a groove into its collar, and the collar itself was then rubbing against the motor housing1. If your noise pattern matches (squeal at start/stop, quiet in between), check disc nut tightness before assuming a bearing.

Cause 4: sticks or debris trapped where you can't see them

Small sticks and fibrous grass/seeds can lodge under the blade discs and collar in spots that aren't visible without disassembly. The dealer notes owners routinely insist "there's nothing under there" until the deck is actually pulled apart1. The fix requires removing the discs, blade guards, and the collar itself to check underneath, a routine part of proper cleaning, not a special procedure. See our cutting-height guide for a step-by-step disassembly procedure covering this same area.

Normal vs. abnormal wobble: the dealer specifically notes that blade discs are supposed to spin and rattle loosely by hand, "like a tambourine": that looseness is by design, not a fault. Don't mistake normal disc play for a problem.

Cause 5: a worn bearing (uncommon on LUBA 2/2X)

If none of the above applies, the remaining possibility is a worn drive-motor bearing, described as a distinct "grinding" or occasionally squeaky sound, not the sharper chatter of blades touching. The dealer notes this was common on the original LUBA 1 but has been rare on LUBA 21, and links it to prolonged exposure to wet grass or standing water. Self-test: remove the blade discs entirely and run the mower in manual mode. If the noise persists with no discs installed, it's coming from the motor itself, not the blades or debris1.

If the self-test confirms it's the motor, that's a repair, not a DIY fix. Contact Mammotion support with your model, firmware version, and the self-test result (noise present with discs removed). See what to have ready before you contact support.
This page reflects one dealer's repair-shop experience across many service calls, not an independently corroborated owner-report pattern. Treat it as a strong first diagnostic path, not a confirmed universal cause for every case. Let us know if your case matched (or didn't).

Sources

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