EMPLOYEE WAS HELPING WITH PRESSING A NEW BEARING INTO A ROLLER MILL ROLL BODY. EE & CO-WORKER WERE USING A PORTAPOWER CHAINED TO THE ROLL BODY. THIS CHAIN IS A LOAD BEARING CHAIN BUT TOO MUCH TORQUE WAS APPLIED & THE CHAIN BROKE & STRUCK EE'S RIGHT FOOT ON TOP JUST BEHIND THE STEEL TOE. X-RAY REVEALS BROKEN BONE (ONE) IN TOP OF FOOT. RESULTED IN HARD CAST/LIGHT DUTY (NO LOST TIME).