by right its a easy thing to do, but it wil dirty ur hands if
not careful..
that time i went to motoshop n change..
the mech unscrew some part or wat, n then he take a plastic
container n put below the 'hole' for the used engine oil black
color one to flow out... finish oredi screw it back, n then open
another cap n pour the new engine oil in...settle liao..
2b bike use normally less than 1 L of engine oil, coming close to 1
L like that lar...
so u go motoshop jus buy a bottle of 1L engine oil from them, they
jus change for u, the remaining oil dunno wat they use for lar.. if
u niao, then take back the remaining oil lor.. 
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