I was looking at possibly doing this over the weekend but I’m afraid it would require a major disassembly/rebuild. Plus, I’m not having these issues.
I wouldn’t recommend trying to swap these pulleys out unless you’re seriously talented in the diy department. 
In case anyone was thinking to replace a smooth idler with a toothed one:
My personal conclusion - it’s easier to print new Y carriages altogether and source new carbon rods somewhere, rather then attemp to disassemble whatever is on the printer.
Also this rises a concern: how does one replace an idler when it fails?
I’m going to see about getting a smooth or serpentine style belt because it’s far easier to swap out the drive motor pulleys in the back
My only concern is belt slippage especially during jerk moves but we shall see
First order of business is finding a belt that’s smooth on both faces then giving it a try running the printer at top speed and checking the print for dimensional accuracy and artifacts
I go back to my initial thought, print a collar for the smooth idler to turn it into a toothed one.
Nono. Changing OD of an idler is a bad idea
Nice test there!
I know Bambu says to print faster but the trade off is matte looking PLA. A lot of times I want that shine, this is the problem for me.
For PLA shiny prints I set outer wall to 100mm/s and increased temperature to 230-235C - I am quite happy with the results.
Could you explain why? All that does in this application is change a belt tension - which is adjustable. You don’t want to change the size of a DRIVE wheel/sprocket/cog/wheel, that would change the speed and torque
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Here is possibility to remove the pins - you need to broke this support, change the idle and glue something to replace the broken pin support. * You need to push locks under bearing to slide it.
I see, you wen one step deeper the I did. 
I am also noticing, that we have different belts. Did the ones on your photo came stock or you did you replace them?
I replaced the belts in attempt to solve the issue. Also, I did everything what I can without braking something. Replacing the idles was last chance, but I didnt receive approve from bambu labs support. So I stopped with this.
FYI, measured the pulleys, 5mm bore, 10mm tall (complete height including flanges) 12mm diameter rolling surface. The 20 tooth should work as long as the flange doesn’t rub on the carriage, but it looks like there is plenty of clearance around it for an extra mm or two. The flange on the ones on the machine is a fair bit narrower and thinner than a regular GT2. Heightwise that doesn’t look to be an issue, but the diameter with flange of a standard 20T is 15mm(Gates brand)16-18mm (generics), which may need to have a bit of the radius trimmed off for clearance. Cant tell though until it’s tried. Diagram here is a Gates GT2 20T idler, 5mm bore.
There would be quality 20T out there where the flange is almost flush with the teeth, so probably around 12mm.
It is a bit off topic but may be interresting to share :
I got my first VFA problem today but it is related to my model and not the printer…
Model in fusion 360 :
Model in Bambu Studio :
Model printed :
There are clear artifact on the big circle while none on the little, facets can be viewed under Bambu Studio.
I am a bit surprise because I never had such problem on curves when exporting from Fusion360 to Bambu Studio especially when using step files rather than stl.
It is not VFA, its a model resolution. You can clearly see that on your image from slicer. Also, here is not 2mm space artifact.
Use export as 3mf, choose hight quality, its better than export step files (for me).
As option - you can play with BambuSlicer>Quality>Precision parameters.
Yes obviously, I said at first, that it was a bit off topic ans related to the model not the printer, anyway thanks for the tips but… IMHO it could be considered as a bug, because the curves in Step files are stored as curves/NURBS and not as faces, so normally no need to specify a quality for Step file as they are already near 100%, that’s why I use Step files (rather than STL or 3MF because they convert models into meshs for saving and then lost the real curves).
The problem is that Bambu Studio convert the model imported into a mesh, I guess : first because it is easier to display even if they could have adjusted number of displayed face based on actual zoom… And second to slice it, this second point is for me a bug they should use curve from model to get G2 & G3 command rather than convert the model to mesh and then re-convert the slices of the model in curves based on a magic parameter …
Here is a comparaison betwen STL and Step :
The solution to my problem is just to set the Arc fitting resolution a bit higher 0.02 rather than 0.012, then it works well, but once again it is a dirty approch to convert a curved model to mesh and then try to guess where the curves was for slicing, rather than directly use the NURBS/curves available from the original Step model.
EDIT : I will go back to STL with a high quality on exported file, but that’s a bit frustrating that Bambulab added STEP files support and that they cannot be used correctly (STEP are not available in other fork of prusaslicer like SuperSlicer and I was pretty happy to be able to use such file format) 
As an exemple here is what the exact same STEP file look like in a 3D viewer software :
Absolutely no faces at all, perfect curves, so the problem is really from the conversion made by Bambustudio from STEP/NURBS to mesh/faces
We agreed that this is off topic. Please stop.
I’m sorry, but you’re wasting your time, my time, and the time of the people who will be looking for a solution here.
They talk a little bit about why they do it here:
3D models are mostly expressed as triangular mesh, which means that the final slicing and printing path are dense line segments. When the printer is slow, these dense paths have no obvious bad influence on print quality. But when printing speed is high, A lot of transient impulse signals will be produced at the turning point of the segment, which brings about noise and vibration.
In order to alleviate this problem, Bambu Slicer generates arc path by fitting within a certain acceptable tolerance.
We agreed that this is off topic. Please stop.
I said a it was “bit off topic” but interresting, I still posted it here because it could easily be confused with VFA, I thinked it was VFA artifacts for about 30 seconds.
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