MAINTENANCE EE WAS COMPLETING BEARING REPAIR ON A 3 DECK INCLINE SCREEN. HE WAS USING OEM THREADED ROD PULLER INSTALLING THE COUNTERWEIGHT SHEAVE ONTO THE SHAFT. WHILE PULLING THE WRENCH TIGHT ENING THE PULLER, HE STRAINED HIS LOWER BACK, PHYSICIAN TREATED ON 8/25/03 WITH HOT/COLD COMPRESSES & MEDICATION.