X Axis Idler / 623h bearing oscillating and making a sharp / squeaking noise

X Axis Idler / 623h bearing oscillating and making a sharp / squeaking noise  

New Member

Hi, I have completed the build of my Mk3S (what fun!!) and have completed 3 successfully/high-quality prints. During the course of these 3 print runs I noticed the X idler / 623h bearing oscillating and making a sharp noise as it rotates.

In terms of testing, I have loosened and then tightened the belt to make sure I have the right tension, but this doesn't appear to resolve the issue.

I have tried to record the issue with the following videos.

I'd be most grateful for the community's thoughts on the issue. Thanks in advance.


Posted : 23/07/2020 5:51 pm
Veteran Member Moderator

The bearing should be centred in the pulley, if it is off centre, you will get similar issues, in my case the bearing collapsed, and that caused my problem, 

I didn't particularly like the design of the single bearing idler. so I looked for, and found twin bearing idler rollers.  they are available in 16 tooth size and 20 tooth size, and either smooth or toothed. 
I chose 20 tooth, GT2 6mm wide, 3mm bearing hole, toothed idlers and use them on all on my printers. 
Mine came from Ebay. 

Regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 23/07/2020 9:13 pm
New Member

Thanks Joan. I didn't realise the bearing inside the idler could be moved. I'll check it and re-align if necessary.

Posted : 24/07/2020 11:15 am
New Member


I had a very similar issue on the Y axis. The idler made this squeaking noise once every full rotation.

It isn't symmetrical. In Ben's video you can clearly see it wobbling around.

I removed the bearing/pulley flipped it over and mounted it again. I also applied some grease on the screw and the side of the pulley where it slightly touches the mounting.

This solved the problem for the time being.

Regards Chris


Posted : 04/08/2020 1:09 pm
New Member

My Y-axis idler also started squeaking a short time after completing my kit build, so I also followed Joan's advice (thanks!) and replaced it with a dual bearing toothed idler.

One tip - if you want to place a washer either side of the idler to stop it rubbing on the support, the standard M3 washer is a little large at 7mm diameter. Look for small diameter washers to DIN433 (for machine screws) which for M3 are 6mm diameter and these will only hold the centre of the bearing with suitable clearance to let the pulley freely rotate.



Posted : 04/08/2020 8:57 pm
Karl Herbert
Famed Member

These pulleys and the bearings used are of very different quality and not optimally suited for this purpose. I have replaced the bearings of the pulleys with higher quality SKF bearings. Alternatively the purchase of a pulley as a replacement would not be bad.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 04/08/2020 9:46 pm
New Member

I am pleased to report that re-aligning the x-idler and changing the tightness of the bolt fixed the problem. Prusa were also kind enough to ship two replacements just in case.

Posted : 04/08/2020 10:12 pm
Active Member

I had something simalar my fix is at tbottom of page 4 of this thread

Posted : 06/08/2020 3:52 pm

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