Grass, about one kilo needed for Hairy Biker (2,4)

I believe the answer is:

si king

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'for hairy biker' is the definition.
I can't tell whether this defines the answer.

'grass about one kilo' is the wordplay.
'grass' becomes 'sing' (both can mean to act as an informant).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'kilo' becomes 'k' (phonetic alphabet: alpha, bravo, charlie etc.).
'i'+'k'='ik'
'sing' going around 'ik' is 'SI KING'.

'needed' acts as a link.

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