I bought a lever machine on CL and this grinder came with it. PO said it was in working condition, which is not a full lie, seeing how the motor does work.
I noticed a wobble and play in the spinning shaft, so I went about trying to salvage this on my own. I first replaced the burrs with new ones. That didn't seem to do the trick, as at the touching point of the burrs, there is a noticeable interference at one point in the spinning.
Next, I tore it apart, which was easier than I thought, and it was filthy. I took the codes off of the previous bearings and bought new ones of higher tolerance. I chuckled when I noticed that one of the 2 bearings was from Korea, the other from Poland. The new ones are japanese and of known quality. Anyway, they slipped off with the help of a 3 jaw puller, and the new ones went on tightly and the whole unit went back together nicely.
So, here's the issue: when grinding fine, as in espresso, the output is granular, and not fine enough to create the powder necessary for good espresso. Any finer on the adjustment dial and the burrs tough and chirp on every rotation. Looking down on the shaft, the bronze fitment there has a noticeable .5mm wobble, despite making sure everything is torqued properly in the assembly. Even with a slight chirp, the output is not fine. I am using a Lido grinder next to it to compare the two against each other.
So, I'd like to hear options at this point. Perhaps its just toast. I'll have a new set of MDX burrs to sell if that's the case. I also 3d printed some feet for it, as well as a funnel shaped hopper for the input chute, as I single dose. I removed the hopper and it didn't come with a doser.
Its odd that when I had the machine apart, and the motor separated from the rest, I plugged it in and made the motor spin, and, to me, it seemed that the shaft was much straighter, and that it didn't wobble like it does when it is mounted in the grinder's frame.

thanks-
p

I'd take the motor back out, mount it in a vise, and then use a set of calipers to check the spinning shaft to be sure it's true/straight. Adjust the calipers to just wider than the shaft, then turn on the motor and check the clearances. If it's not spinning true, then it's new motor time. If it does spin true, then there must be a problem with either the burr set or the motor mounts. Do you have an old set you can try to check for wobble?

The rotating burr carrier may be canted and is no longer at right angles to the shaft. This may be due to previous attempts to remove it from the shaft or a reinstallation problem.

The first step will be to determine exactly where the obvious misalignment originates. It looks as it would be possible to remove everything from the motor shaft and then hand turn the shaft with a pointer close to the shaft so as to easily detect any runout. If the shaft runs true then the rotating burr carrier is suspect.

Thanks for the advice, I will try to use the vice to mount the motor and put a set of calipers on the shaft to see if I can see wobble occurring.
I do have the older set of burrs, they too cause a similar rotational chirping noise when the adjuster has them close enough to touch. The new burrs make less noise than the older ones do, but they both seem to show an off axis situation. I also tried rotating each burr independently, as there are three screw holes and two burrs. No combination there seemed to cure the problem.
Now I know that the burrs have to touch in one spot when put in proximity to each other, its just that with the way this is happening, its an easy way to tell if the burr sets' faces are getting close to being parallel to each other.
I wonder if a shim could be used to offset the angle. That could be lower in cost than a new motor and shaft.

And, for anyone wondering about replacement of bearings on a grinder motor shaft, well, its dead easy to do. With the right tools and new bearings, its a 20 minute job.

You do not need to clamp the motor in a vice, just expose the shaft and hold a pointer close to the side of shaft and rotate by hand. If it is bent you can see it. If it is not bent then the problem is in the rotating burr mount. You have 2 places that could be causing this problem, maybe 3 as the non rotating burr carrier may not be set parallel to the rotating carrier.

I have found the issue to be the burr carrier. There is nothing wrong nor wobbly when the motor turns the shaft itself. When I assemble the burr carrier to the shaft and lock it in place with the bronze nut, its apparent that the carrier is out of alignment. It wobbles badly in a pringle fashion. Perhaps the carrier is not seating itself perfectly perpendicular to the shaft, but its good to know that the motor and axle are fine.
Does anyone know where to obtain a new lower burr carrier for an MDX?

thanks
p

Here is a test of the grinder on my bench, with the wobble:
https://youtu.be/VMBFBCVvAIM

Sounds like a trip to your local machine shop is needed. Or a member here that just happens to have a lathe in their shop. The rotating burr holder can be mounted in a lathe using the bore of the holder as the centerline. The mounting face and the face that mates against the inner race of the bearing can be faced to restore the perpendicularity you are after. Bird chirps are fine out in the back yard but not in a grinder...
jpboyt