Hello,

I am still relatively new to espresso and am looking for some help on diagnosing a grinder problem that arose yesterday. I have a used La San Marco SM-90 from 1995 that had been working well until something got into the grinder (maybe a rock?) and caused the burrs to lock up suddenly. I stopped the grinder immediately, but after switching it on again, I noted the motor turning and a rattling noise emitting from the grinder. I took off the top burr and noted that the bottom burr no longer spins despite the motor moving. Prior to this, I had noted a bit of a rattle as the lower burr slowed down after use, but nothing persistent.

I presume it could be a number of issues and/or parts failing along the driveshaft, bearings, up to the lower burr assembly. Might anyone have some input on possible diagnoses given this limited amount of info, parts that could be affected, and if I should even attempt to disassemble and take a look at the assembly (is it complicated enough that I risk being unable to put it back together, though I'm usually pretty handy with disassembling machines)?

Thanks in advance for any advice!

stc3 wrote:I took off the top burr and noted that the bottom burr no longer spins despite the motor moving.

I am interested in buying a used San Marco grinder and saw your thread. Hopefully this is a part designed to break, and would be called a shear pin, machinists use it frequently. It's a concept that a cheap part breaks and saves the more expensive components. Breville grinders achieve this same level of protection by stripping the sacrificial plastic gears. The problem is in studying the parts list, I don't see a shear pin or sacrificial plastic gears in the design.

https://www.espressoparts.com/parts/esp ... nder-whole

If I had the unit I would tear it down to see if there was a shear pin or if a more expensive motor component separated.

usually bigger coffee grinders like bunns have the shear plates. I don't think most vertical motor espresso machines have them.
Mazzer style grinders have the motor shaft run up through the case and the bottom burr mounts directly onto it.
I have taken a bunch of these guys apart, and I usually end up clamping something onto the fan blades at the butt of the motor to keep the shaft from spinning to remove stuck bottom burrs.

If you are lucky, maybe it is the screw/bolt that holds the lower burr carrier to the motor. If you're not lucky, the bad bearing sheared the motor's shaft. Hard to tell from the diagram. In any case, a teardown is in order. You will at least need to pull the motor assembly out to see what's going on.