Modern Vespa

Do guys ever replaced the bearing brass seat? Is it worth to replace? Just to make sure the bearing will sit at the best condition

I think charlieman tackled this somewhere around page 78 or 79 ...

Vintage vespa with sidecar (**Now In Technicolor ! **)

I got a little carried away on mine...
If you don't plan to buy a mill, and a lathe, and teach yourself to machine, and weld, then there are simpler solutions.
And simple is good.

At issue: if that bronze ring moves (as your's clearly has...) it's bad.
You can put it back in - but without any treatment - you may find that it fails when you install your main bearing.

Making this tougher: when you heat the cases to allow your cold bearing to fit - the bronze ring will loosen and move.

Here is a trick.
Instead of installing the bronze ring back in place, then the bearing, do it this way:
Install the bronze ring perfectly on your bearing outside the motor.
Do it on a hard very flat surface so you know you have it flush and perfectly square.

Now heat the cases as you normally would - and chill the bearing WITH the brass ring on it.
To keep it dry - put it in a sealed bag - but put that bag in the freezer.
Get some "retaining compound" from loc-tite.
Put it on the outside of the bronze bearing just prior to insertion to the heated aluminum case.
Use something large enough that presses the bronze bearing and the main bearing in one push (that is - don't just push on the bearing as it will unseat from the bronze.

The retaining compound will help hold your bronze in place once its pressed in to the cases like this. Single press and you are done.
Hope that helps.
-CM