When removing clutch system large or small system to replace corks.  It is recomended you remove from the non cogged end.  The cogged end is set up with the correct spacing for the chain.  Also never get your clutch disc machined as they are not supposed to be perfectly flat.  Uneven surfaces have more grip than flat.  You may use very fine wet and dry doing small circles to take any sharp pieces off and to get better grip.