Ducati MONSTER 821 Workshop Manual page 996

Remove from the cylinder head stud bolts the four O-rings (A) (one per stud bolt) located on the crankcase
between cylinder and gasket (11) and replace them with four new O-rings (A) by inserting them inside
their seats (C) using tool (D).
To remove the horizontal cylinder-piston assembly, bring the vertical piston to TDC and proceed as for
removal of the vertical cylinder.
Important
Mark the pistons to show from which cylinder they were removed:
V= Vertical - O= Horizontal.
996 Ducati Manuals Resource