Ducati Monster 796 Workshop Manual page 563

Cylinder head assemblies: valves - rocker arms
Visually inspect the valve seats: there must no excessive hollowing and there must be no pitting or cracks.
If a valve seat is slightly damaged, it may be lapped using the special 45° lapping tools, with subsequent grinding of the
valves and leak test.
If the valve seats are excessively damaged, fit oversize seats. Replacement seats are available with 0.03 and 0.06 mm
oversized outside diameters.
Important
When you change the valve seats, change the valve guides as well.
Renewal of the valve seat
Remove the worn seats by grinding out the rings. Take great care not to damage the valve seat housing in the cylinder
head.
Check the diameter of head bores and choose the oversized valve seat that will give an interference fit of 0.11 to
0.16 mm. Replacement valve seats are supplied in outside diameter oversizes of 0.03 and 0.06 mm.