PIAGGIO Beverly Tourer 300 i.e. Service Station Manual page 160

Engine
Studs
Check that the stud bolts have not worked loose
from their seat in the crankcase.
Check the depth of stud bolt driving with a gauge,
as indicated in the picture. If it varies significantly
from the driving depth indicated, it means that the
stud bolt has yielded.
In this case, replace it.
ENG - 160
Beverly Tourer 300 i.e.