Prusa i3 Mk3S+ Squealing-Squeaking-2022-02-21

Has anyone else had this issue and if so, what solved it? My Prusa i3 Mk3S+ started squealing and squeaking like a mouse catch in a compression trap that was not totally efficient in its purpose. I may have solved it. The belt tension was good, there was no interference under the bed, nothing out of place or loose. I took the forward Y belt pulley off, it rotated freely and smoothly. I applied a bit of the Prusa supplied lubricant to it and reinstalled it. At the moment it is quieter and has been running for about 10 minutes.

YouTube video of what this printer sounded like.

Prusa i3 Mk3S+ squealing and Squeaking-2022-02-21 - YouTube

Comments? Suggestions?


Printing 100,000 hours. :arrow_right: Perform a little maintenance. :grin:

In chasing the squeaking and squealing last night, I found nothing relevant or reasonable but questions on the Prusa forum. And I found nothing on YouTube – that will change shortly. Using a solid rod trying to locate the source of the noise kind of failed – an old mechanic’s repair trick. However, it did isolate it to the forward assembly area. Sealed bearing have a really good history – depending on their manufacturer. The Prusa i3 Mk3S+ seems to have really good quality parts so I had confidence in the bearings. The other issues is USUALLY, not ALWAYS, when a sealed bearing fails that is under single line or vector stress the issues appear regardless of the direction of rotation and this squeaking and squealing was when the hotbed was moving forward, not rearward. The noise was not associated with extruder height above the bed or extruder position in relation to the X axis.

My printer gets a lot of use. It averages over 9 hours a day of printing for the last 190+ days, so it has over 1,700 hours of print time. I clean the exposed elements fairly often and every once in a while put one dot of the Prusa lubricant on the rods the carriage rides on.

So I got more curious, while waiting for Prusa support to come back with an answer. I released the tension on the Y axis belt and removed the forward bearing from the Y Belt Idler. While it is a SMALL bearing, I could not detect any issue with its rotation. The second element of its rotation is the machine screw going through that bearing. One dot of Prusa lubricant on the insertion side of the bearing and worked the machine screw through it several times to distribute the grease before reassembling the idler on the printer. Then reset the tension on the belt.

At the outset of a 1 hour 15 minute print last night it was still squeaking and squealing but noticeably less. This morning, one 2 hour and 34 minute print complete, a second 1 hour 19 minute print in progress back to its almost quiet printing mode.

So there appeared to be an issue of free rotation with the forward Y axis idler pulley. I suspect that there was too much resistance between the machine screw and the bearing with the bearing being slightly out of exact alignment with the belt pull.

Photos provided, in my assembly manual they are pages 21, 22, and 23, associated with Assembly Steps 12 thru 15.

To answer a question, Why noise while moving forward and not rearward? When the hotbed is moving rearward the tension is on the top of the forward Y axis belt idler pulley. When the hotbed is moving forward the tension is on the bottom of the forward Y axis belt idler pulley. In resolving front end noises in rear wheel drive cars, the owners would complain about noises and vibrations while turning right but not left or going straight, or while turning left but not while turning right or going straight. The axle bearings were under different stresses turning left, or right, or going straight.

Prusa i3 Mk3S+ Manual Page 8-2022-02-22

Good analysis and apparently “A little dab’s do ya!” :joy:

Go Brylcreem!!!

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Seems a very odd way to use a bearing from the pictures. Bearings spin on their sleeve.

  1. you want the sleeve captured so it does not move and the bearing does.f
  2. you want the bearing and that attached to the bearing to not rub on anything while it’s moving.

Looks like they failed in both cases by letting the bearing sleeve spin on the M3x18 screw and there’s nothing holding the bearing/sleeve centered in that mount so the sides of the idler(holding the bearing) can rub on the mount.

you can lub up the m3-18 screw and put lube on the side of the idler bearing mount but the better solution is to put spacers on the m3-18 to the bearing sleeve is held from turning and held in the center of the idler mount.

Agree there could easily be better engineering in the Prusa printer. Happy with most of it, would love to put in a few engineering change orders or production change orders into the system.

Resolved the issue and posted a video.
Prusa i3 Mk3S+ Squealing and Squeaking-2022-02-23 - YouTube

Bearings should be press fit to preclude shifts when being put under tension. Bushings or washers (less precise) may help keep the bearing in proper alignment. That is going to be an issue because this is a sunken hub bearing. So the bushing or washer has to fit inside and clear the pulley or it will create friction between the pulley and the housing.

The width of the slot in the housing is probably less than 0.10 mm wider than the pulley. Not much room. Maybe next time.

Up and running quietly again.


normally the spacers are the same size as the bearing center sleeve because if they are any wider they can start to interfere with the bearing seal/covers.

Fix would be to remove 2mm from each of the inside faces of the mount and 3D print little tubular spacers. Placing the spacers in the pulley and slip into position. Shouldn’t take too much to get one side spacer and the bearing in place while the 2nd spacer might take some fiddling. Maybe even a piece of paper used to move it onto the m3x18 as it’s slid through.

I hope the bearing isn’t also floating in the pulley. Maybe s sheet of very thin teflon tape on each side of the pulley will give it some dry lubrication against the plastic mount…

BTW, the main purpose for the spacers on each side of the bearing is so that the spacers, center bearing sleeve(race) lock together as one part and press against the mount so that none of these parts move. There should be no rotation of anything on the m3x18 screw and what is supposed to move is the pulley attached to the outer ring of the bearing and the bearing cage. Not the center race.