Ducati Diavel Workshop Manual page 711

Cylinder head assemblies: valves - rocker arms
Refitting the valves, closing shims and half rings
Carefully clean the two intake valve seats (A) and the two exhaust valve seats (B).
Lubricate the stems of the two intake valves (14) and of the two exhaust valves (11) with engine oil.
Warning
Apply engine oil to the valve stems, however only in the area shown, making sure not to smear the grooves (V).
Install the valves in respective seats in the cylinder head.
Hold the closing rocker arm (16) pushed downwards and fit the closing shim (7) on the valve stem up to reach the rocker
arm. If using the old cylinder head, start by fitting the original shim.
Insert the new half rings (6) in the valve groove (T) and release the rocker arm to obtain shim (7) internal position. Turn
the closing rocker arm (16), and compress the spring as much as possible while holding the valve, the shim and the half
rings in the valve closed position. Release the rocker arm with a rapid motion, so that the half rings seat in the shim.