THE 2ND SHIFT MECHANIC WAS WORKING W/SHOP FOREMAN TO REMOVE AN AIR MOTOR OFF OF A 632 EIMCO MUCKING MACHINE. THE MOTOR HUNG ON THE ALIGNMENT PINS. SHOP FOREMAN WAS TAPPING MOTOR OFF THE PINS W /A HAMMER WHILE MECHANIC WAS HOLDING IT. IT CAME OFF PINS & SLIPPED OUT OF MECHANIC'S GRIP, HE REACHED OUT TO GRAB IT & SMASHED HIS FINGER, RESULTING IN LACERATION & FRACTURE TO MIDDLE FINGER