A baler comprising: a main bale chamber having upper , lower and side walls , said main bale chamber having an outlet for discharge of compressed crop material into bales ; a plunger reciprocable within said main bale chamber between a first position away from said outlet and a second position towards said outlet , said plunger having an end face with a lower and a upper edge for compressing crop material in said main bale chamber ; a mechanism for reciprocating said plunger within said main bale chamber between said first and second positions; an opening in one of said walls having a front edge and positioned to permit entry of crop material into said main bale chamber when said plunger is in said first position , the lower edge of said plunger end face sweeping over said opening when said plunger is translated between said first and second positions ; a first guide mechanism for translation of said plunger between said first and second positions, said first guide mechanism permitting pivoting of said plunger about an axis substantially parallel to the front edge of said opening ; characterized by: a second guide mechanism connected between at least one of said main bale chamber walls and said plunger , said first and second guide mechanisms (82, 84 ; 88, 92) cooperating to : - place said plunger in a first orientation so that the upper edge of said plunger end face compresses crop material first when said plunger is in said first position and, while said plunger moves between said first and second plunger position , - orient the plunger end face to a second orientation so that both edges compress the crop material equally, and wherein said second guide mechanism providing a predetermined translation from said first to said second orientation. a main bale chamber having upper , lower and side walls , said main bale chamber having an outlet for discharge of compressed crop material into bales ; a plunger reciprocable within said main bale chamber between a first position away from said outlet and a second position towards said outlet , said plunger having an end face with a lower and a upper edge for compressing crop material in said main bale chamber ; a mechanism for reciprocating said plunger within said main bale chamber between said first and second positions; an opening in one of said walls having a front edge and positioned to permit entry of crop material into said main bale chamber when said plunger is in said first position , the lower edge of said plunger end face sweeping over said opening when said plunger is translated between said first and second positions ; a first guide mechanism for translation of said plunger between said first and second positions, said first guide mechanism permitting pivoting of said plunger about an axis substantially parallel to the front edge of said opening ; characterized by: a second guide mechanism connected between at least one of said main bale chamber walls and said plunger , said first and second guide mechanisms (82, 84 ; 88, 92) cooperating to : - place said plunger in a first orientation so that the upper edge of said plunger end face compresses crop material first when said plunger is in said first position and, while said plunger moves between said first and second plunger position , - orient the plunger end face to a second orientation so that both edges compress the crop material equally, - place said plunger in a first orientation so that the upper edge of said plunger end face compresses crop material first when said plunger is in said first position and, while said plunger moves between said first and second plunger position , - orient the plunger end face to a second orientation so that both edges compress the crop material equally, <EOS>