a tale of the third rail

My second Prusa i3Mk3S (Prusa B) had another restricted movement event. The Y-Axis became stiff and jammed causing a crash detected print fail.

Update 2021-01-24: I contacted Prusa Customer Service with the details and photos of the bearing issues. Prusa sent me replacement bearings: good customer service!

Y-Axis

Symptoms

1. Y-Axis stiff.
2. Failed Print.
3. Crash detected.

Diagnosis

1. Removed:
   1. Build plate
   2. Heated bed.
2. Checked bearings: Left two bearings running rough and stiff.
3. Bearing seal debris underneath printer again!

Bearing seal spoor, running rough, stiff: probably two defective bearings.

Treatment

With the heated bed already removed after diagnosis:

1. Removed bearings:
   1. Cut Rail tie-wrap at the rear end,
   2. Tilted the rail
   3. Loosened the u-bolts (from each u-bolt: one nut removed completley, the other slacked), and
   4. Slid off the bearings.
2. Replaced bearings:
   1. Cleaned Rail,
   2. Slid on the two new bearings,
   3. Positioned them,
   4. Re-tightened the u-bolts,
   5. Tie-wrapped the rail.
3. Slid the Y-Axis about a bit to make sure that all seemed correct.
4. Re-tightened the Y-Axis belt adjuster as I felt that this was a little slack.
5. Calibration -> Wizard: all OK.
6. Calibration -> First layer cal.

Note: I did as little work as possible. It could be more correct to fully remove the heated bed and rail to avoid damage to the printer. I also did not remove the Right-hand rail, or replace the Right-hand bearing. My method worked but it may not be the best engineering practice.

I used the Z adjust value that I had last used and it came out ok.

First print: M10 nuts and bolts, 0.4 nozzle, 0.2 layer height (thread test an 0.2), PET-G, Amazon Filament. Printed OK.