Y-axis belt loosening

I recently found the y-axis belt on my Ender 3 V3 KE was extremely loose. It had no tension on it whatsoever. I watched the video on changing the belts and tightened the belt using the screw on the back of the base such that if I pluck either side it makes a low noise like a low guitar string. However, after running the printer, I discovered the belt had loosened, not to the point where it had not tension, but it was clearly looser than I had set it before printing. This happens every time I tighten the belt and since it happens as I am printing, my prints are being impacted. Is there some other screw besides the one at the back of the base I need to adjust or tighten to keep the belt from loosening?

Update: When I asked Creality CS where the eccentric screw as located, they told me that I needed to tighten the tension screw and included a picture showing the screw at the back of the base that I told them I had previously tightened. Oh well…I suggested that maybe the tensioner itself is defective as @amberhelios suggested, and asked if this was something they could send me (along with a fan replacement kit they are already sending me).
I contacted Creality Customer support and this is what they said: besides tightening the screw at the back of the base, you may need to check and adjust the eccentric nut on the y-axis. This nut is located on the side of the printer’s frame and is responsible for tensioning the belt properly. By adjusting this nut, you can ensure that the belt remains tight and maintains the correct tension for smooth printing without loosening.
I was not able to find anything like this on the printer and also did not see any reference to an eccentric nut in the video about changing the x and y-axis belts. Is there an eccentric nut for the KE/SE printers? If so, where exactly is it located? Thanks!

Not on my SE. I’ve just replaced the belt

Not sure how exactly the belt tensioner looks like on the KE but maybe you can print something like a clip that keeps the screw from rotating. Or screw in a counter nut if that could work and you have one. Eccentric nuts should not be related to this issue.

Have you tried taking the tensioner off, maybe the heat insert is loose to the screw and that’s why it’s not keeping, its brass and maybe the screw is pulling out due to bad threads. At least that way you can say this is what is happening and they can send you another

Just a thought

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Update: Creality CS is sending me a replacement tensioner. It took a bit of back and forth, but CS came through! Thanks Creality!


The tensioner on the KE is exactly the same as the SE. No idea about the eccentric nut comment. Adding a lock nut might work, just space is limited. Might be better to use some thread lock “gunge”, not the super sticky one but one that just binds the screw a bit. Perhaps a bit of plumbers PTFE.