Benny had been binary bonded to Mr. Bamt in Season one.  Changed by the Key, he touched Mr. Bamt's dying frame. It was at that moment that part of Mr. Bamt's spark fled into Benny.   The spark compelled Benny to construct a new form for Mr. Bamt... and thus Action Master Mr. Bamt was created. Now, Mr. Bamt has dedicated himself to neither the Vehicon or Maximal cause... but to his own.  The defense of Cybertron.  The capabilities of his new form have yet to be shown, but since it was constructed partially from the salvaged remains of a Quantum Transwarp shuttle... anything is possible.