Ducati MONSTER 821 Workshop Manual page 969

Insert the new split rings (5) in the valve groove (T) and release the rocker arm to correctly position shim
(6). Turn the closing rocker arm (3), and compress the spring as much as possible while holding valve,
shim and split rings in the valve closed position. Release the rocker arm with a quick movement, so that the
split rings seat in the shim.
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