I recently acquired a used la San Marco sm90 with brand new burrs. When brought down to some of the finer settings the beans would jam the motor. I went through all the normal things to check. I did get the original burrs with the machine, and took the new ones out to compare. I could clearly see the new ones have a significantly more aggressive profile on the inner edges, the ones the beans contact first. I stuck the original burrs back in (which weren't in bad shape really) and it works perfectly fine. I can't find any info on this really. The burrs were purchased from espresso parts.com and they haven't heard of this. Any ideas on why this is and where I could find the profile of the original burrs?

New burrs will take time to break in, this is called seasoning and is normal. Brand new burrs aren't ideal, but they are a necessity if the old burrs are too far worn. If your old burrs are fine, there's no reason not to use them. Burrs take a while to season, especially in a home setting. And your old burrs should likewise take a long time to wear out, but of course depends on how worn they are now.

This isn't a break in issue. The profile of the initial teeth are about 1.5mm taller on each side. The machine won't even start. Beans fall and sit against these much taller teeth and jam the motor. The old burrs are much flatter on the initial teeth allowing it to start spinning. While the old burrs are still ok currently, they are dulling and will begin to become inconsistent soon, so I need to find another pair.

Oh I see, must have missed the jamming the motor comment above...

You could always break out some files Unless you can return the new burrs...

Can you post a side by side pic of the burrs? That's interesting.

Are you trying to start the motor with beans already in the hopper or starting it up first then pouring the beans in second? If you try it the latter way and it still stalls, you may have an issue with the motor. Could be that the less aggressive profile on the old burrs masked that issue.

You could also try to run a kilo or two of minute rice to "season" the new burrs.

Solved the issue. Turned out that while the new burrs are more aggressive than the old, problem was actually the start capacitor wearing out. It wasn't supplying enough torque to the motor on startup. The older less aggressive burrs required less torque initially and masked the wearing start cap.

That's what I was expecting. Glad you got it sorted in the end.