A crusher unit includes a mainframe that supports a crusher suitable for crushing bulk material. The unit has a primary motor carried by the frame to drive a crusher via a first drive belt extending around a first drive pulley and a first flywheel mounted at the crusher. The unit further includes a secondary motor carried by the frame to provide a secondary drive to the crusher via a second drive belt extending around a first or a second flywheel mounted at the crusher and a second drive pulley.