Ducati Diavel Workshop Manual page 726

Cylinder/piston assemblies
pin.
The gudgeon pin (3) must slide smoothly in the connecting rod small end bush and in the piston (1).
Close the crankcase opening with a cloth to prevent foreign objects from falling inside and then fit the retainer ring (2) as
shown in the figure.
Important
Always fit new circlips (2) on reassembly.
Push the cylinder barrel (10) down until it seats against the crankcase.
Refit the bushes (12).